
==== Front
BMC Cancer
BMC Cancer
BMC Cancer
1471-2407
BioMed Central London

39266997
12884
10.1186/s12885-024-12884-5
Research
Salvage chemotherapy regimens with arsenic trioxide for relapsed or refractory neuroblastoma: a promising approach
Liu Xiaoshan 1
Peng Xiaomin 1
Yang Shu 1
Liu Haijin 2
Zhang Shouhua 3
Wang Jinhu 4
Ma Yuhan 1
Wu Yu 1
Wang Zhixuan 1
Weng Wenjun 1
http://orcid.org/0000-0002-1756-5847
Li Yang drliyang@126.com

1
1 grid.412536.7 0000 0004 1791 7851 Pediatric Oncology, Children’s Medical Center, Sun Yat-Sen Memorial Hospital, Sun Yat-Sen University, No.107, Yanjiang West Road, Yuexiu District, Guangzhou, 510120 Guangdong China
2 Department of Pediatric Surgery, First Affiliated Hospital of Gannan Medical University, Gannan Medical University, Ganzhou, 341000 Jiangxi China
3 https://ror.org/03tws3217 grid.459437.8 Department of General Surgery, Jiangxi Provincial Children’s Hospital, Nanchang, 330006 Jiangxi China
4 https://ror.org/025fyfd20 grid.411360.1 Department of Surgical Oncology, Children’s Hospital Zhejiang University School of Medicine, Hangzhou, 310052 Zhejiang China
12 9 2024
12 9 2024
2024
24 114026 6 2024
2 9 2024
© The Author(s) 2024
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/.
In patients with relapsed or refractory neuroblastoma (NB), the limited efficacy of conventional chemotherapies necessitates the exploration of new treatment options. Previous studies have highlighted the anti-tumor properties of arsenic trioxide (ATO) in high-risk NB (HR-NB). This study aims to assess the effectiveness and safety of ATO combined with salvage chemotherapy regimens, featuring cyclophosphamide and topotecan, as a foundational treatment for children with relapsed or refractory NB. Eleven patients (four relapsed, seven refractory NB) were retrospectively analyzed for efficacy and treatment relevance. Salvage treatments, incorporating ATO (0.18 mg/kg daily for 8 h intravenously on days 1 to 10), were administered upon disease progression or relapse, with assessments conducted every two cycles. Treatments had 63.6% efficacy, with six cases of partial response, one case of stable disease, and four cases of disease progression. The overall response rate was 54.5%, and the disease control rate was 63.6%. Importantly, the systemic toxicity experienced by patients following salvage chemotherapy with ATO was mild. Salvage chemotherapy regimens featuring ATO demonstrated potential for prolonging disease stabilization for relapsed or refractory HR-NB patients, exhibiting both favorable efficacy and safety profiles. This suggests further clinical exploration and promotion of this therapeutic approach in the treatment of NB.

Clinical perspectives summary

Point 1. The inadequate effectiveness of traditional chemotherapy in individuals with recurrent or resistant neuroblastoma (NB) necessitates the investigation of novel therapeutic approaches.

Point 2. Arsenic trioxide (ATO)-based salvage treatments are both effective and less toxic in relapsed or refractory NB.

Point 3. Salvage chemotherapy regimens incorporating ATO have shown promise in extending disease stabilization in relapsed or refractory high-risk NB patients, with favorable efficacy and safety profiles, which suggests further clinical exploration and promotion of this therapeutic approach in the treatment of NB.

Keywords

Neuroblastoma
Arsenic trioxide
Relapsed
Refractory
Salvage chemotherapy
Guangzhou Area Clinical Specialty Technology Program2023P-TS39 Sun Yat-Sen Medical–Industrial Integration Cultivating ProgramYXYGRH202203 Heilongjiang Harbin Yida Pharmaceutical Co.7670020013 issue-copyright-statement© BioMed Central Ltd., part of Springer Nature 2024
==== Body
pmcIntroduction

Neuroblastoma (NB) is the prevailing extracranial solid tumor observed in pediatric patients, arising from primitive neuroblasts and manifesting at various locations within the sympathetic nervous system [1]. It constitutes approximately 7–8% of the prevalence of childhood malignancies and contributes to 15% of cancer-related mortality in the pediatric population [2]. NB demonstrates significant biological and clinical heterogeneity, as children classified as low-risk exhibit a favorable prognosis, and in certain instances, tumors may exhibit spontaneous regression [3]. However, nearly half of patients are diagnosed with high-risk NB (HR-NB), a condition characterized by the prevalence of bone or bone marrow metastasis in individuals older than 18 months or MYCN amplification regardless of age [4]. Despite the implementation of a multidisciplinary sequential comprehensive treatment regimen encompassing chemotherapy, radiotherapy, surgery, immunotherapy, and hematopoietic stem cell transplantation (HSCT), the five-year survival rate for patients with HR-NB continues to be below 50% [5]. Treatment failure is predominantly attributed to the presence of multiple drug resistance (MDR), which poses a significant obstacle in achieving successful curative chemotherapy [6]. The mechanisms underlying resistance to NB cells are intricate and diverse, encompassing factors such as tumor burden and growth kinetics, tumor heterogeneity, untargetable cancer drivers, the immune system and the microenvironment, and physical barriers, among others [7]. The occurrence and development of NB have been shown to be influenced by aberrant mutations in genes such as MYCN, as well as dysregulation of signaling pathways including PI3K/AKT/mTOR, WNT/β-catenin, P53-MDM2, and RAS-MAPK [8]. These genetic and signaling abnormalities have also been identified as mechanisms contributing to chemoresistance in NB. The prognosis for patients diagnosed with relapsed or refractory NB is unfavorable, owing to the restricted availability of efficacious conventional chemotherapeutic treatments. Consequently, it is crucial to formulate novel therapeutic regimens for these patients with the aim of enhancing response rates.

Arsenic trioxide (ATO), a traditional Chinese medicine with a long-standing history of over 2,400 years, has been utilized for the treatment of acute promyelocytic leukemia and has also been investigated for its potential efficacy against various solid tumors, such as NB [9]. The anti-tumor mechanisms of ATO encompass a range of actions, including the inhibition of cell proliferation, induction of cellular differentiation, down-regulation of B-cell lymphoma 2 protein expression, suppression of tumor angiogenesis, and inhibition of telomerase activity. In a similar vein, our research team has been diligently investigating the potential therapeutic efficacy of ATO against NB. Our previous research has demonstrated that ATO functions as a chemotherapeutic potentiator, effectively enhancing its cytotoxic effects when combined with mitotic-specific antitumor agents (vincristine or docetaxel) or non-mitotic-specific antitumor agents (etoposide or cisplatin) [10]. This potentiation is achieved by inducing cell cycle arrest in NB cells in the G2/M phase. ATO has the potential to impede the expression of drug-resistant proteins, such as p-gp proteins, thereby counteracting chemoresistance [11]. Furthermore, Chen S et al. [12] have reported promising findings indicating that ATO can restore the functionality of structurally mutated p53 through cryptic ectopic sites. Our previous clinical studies have also revealed that the combination of ATO and chemotherapy yields a substantial enhancement in the terminal induction response among patients diagnosed with high-risk NB, which can be considered a viable alternative treatment for HR-NB, presenting novel prospects for patients to extend their survival [13, 14]. As previously stated, the utilization of ATO either independently or in conjunction with chemotherapeutic agents presents a potentially encouraging therapeutic approach for addressing relapsed or refractory NB. The present study aims to assess the effectiveness and safety of ATO combined with a salvage chemotherapy regimen based on cyclophosphamide and topotecan for the treatment of relapsed and refractory NB in children.

Patients and methods

Eligibility

Patients under 18 years of age diagnosed with HR-NB, as confirmed by the revised neuroblastoma classification established by the Children’s Oncology Group (COG) in 2021 [15], were deemed eligible for inclusion if they exhibited one of the following responses to prior chemotherapy: either relapsed disease or refractory disease, defined as progressive disease (PD) or stable disease (SD) following a minimum of four induction courses.

Patients with previous total body irradiation, allogenic transplant, pregnancy, breastfeeding, active or uncontrolled infection, previous noncatheter-associated deep venous thrombosis, or active diarrhea were excluded.

Study design and treatment

This retrospective, single-center case series was conducted between January 2021 and July 2022, involving 11 pediatric patients with relapsed or refractory HR-NB. No randomization was planned for this study. The study received approval from both the protocol review committee and the institutional review board of Sun Yat-sen Memorial Hospital. Each patient obtained written consent approved by the Ethics Committee of Sun Yat-sen Memorial Hospital from their legal guardian. No blinding was applied.

In this study, patients enrolled underwent the compulsory baseline examination, including a complete physical examination, serum neuron-specific enolase (NSE), urinary vanillylmandelic acid/creatinine (VMA/Cr) ratio, serum lactate dehydrogenase (LDH), computed tomography (CT), and magnetic resonance imaging (MRI) or positron emission tomography (PET) CT, at the time of initial admission. Patients underwent gene sequencing if necessary.

All eligible patients received salvage therapy containing ATO (regimen A or regimen B) for a total of six courses, with arm 1 and arm 2 alternating sequentially in each. Regimen A was the first option to be considered. Patients who failed to achieve complete response (CR) or partial response (PR) after four cycles of regimen A chemotherapy would receive regimen B. Notably, standard hematologic criteria for initiating chemotherapy were met when the patients’ neutrophil count exceeded 1.0 × 109/L and platelet count exceeded 1.0 × 1011/L. Courses of chemotherapy were spaced 28 days apart (counting from day 1 of chemotherapy).

In regimen A (Table 1) and regimen B (Table 2), ATO was administrated at a dose of 0.18 mg/kg per day for 10 days. The ATO injection was administrated at a constant rate over 8 h in 250–500 ml of normal saline or a 5% glucose solution through a central vein. Regimen A further included topotecan (Topo), vincristine (VCR), and cyclophosphamide (CTX) in arm 1, and Topo, CTX, and etoposide (VP-16) in arm 2. Regimen B included Topo, CTX, and vinorelbine (VNL) in arm 1, and Topo, doxorubicin liposomes, and VNL in arm 2. The specific medication regimens are detailed in Tables 1 and 2. Patients also received 0.5–1.0 g ascorbic acid along with 5% 100- to 250- ml glucose injection in another vein channel.

Table 1 Dose and usage of chemotherapeutics of regimen A

Drug	Dose and Usage	Time	
Arm 1			
 ATO	0.18 mg/kg·d, IV drip, PI = 8 h	d1-d10	
 Topo	1.5 mg/m2·d, IV drip, PI = 24 h (light-avoidance)	d3-d5	
 VCR*	0.034 mg/kg·d or 1 mg/m2·d, IV drip, PI = 2 h	d3-d4	
 CTX	1.2 g/m2·d, IV drip, PI = 3 h, after using VCR	d3-d4	
Arm 2			
 ATO	0.18 mg/kg·d, IV drip, PI = 8 h	d1-d10	
 Topo	1.5 mg/m2·d, IV drip, PI = 24 h (light-avoidance)	d3-d5	
 CTX	150 mg/m2·d, IV drip, PI > 1 h	d3-d5	
 VP-16	100 mg/m2·d, IV drip, PI > 4 h	d6-d8	
Abbreviations: ATO: arsenic trioxide; CTX: cyclophosphamide; Topo: topotecan; VCR: vincristine; VP-16: etoposide; * Take the lower value of the two calculation methods; maximum dose = 1 mg/day

Table 2 Dose and usage of chemotherapeutics of regimen B

Drug	Dose and Usage	Time	
Arm 1			
 ATO	0.18 mg/kg·d, IV drip, PI = 8 h	d1-d10	
 Topo	1.5 mg/m2·d, IV drip, PI = 24 h (light-avoidance)	d3-d5	
 CTX	1.2 g/m2·d, IV drip, PI = 3 h, after using VNL	d3-d4	
 VNL	25 mg/m2·d, IV drip, PI = 20 min, dilution concentration of dilute ≯ 1 mg/ml	d3	
Arm 2			
 ATO	0.18 mg/kg·d, IV drip, PI = 8 h	d1-d10	
 Topo	1.5 mg/m2·d, IV drip, PI = 24 h (light-avoidance)	d3-d5	
 Doxorubicin liposomes	20 mg/m2·d, IV drip, PI > 3 h, after using VNL	d5-d6	
 VNL	25 mg/m2·d, IV drip, PI = 20 min, dilution concentration of dilute ≯ 1 mg/ml	d5	
Abbreviations: ATO: arsenic trioxide; CTX: cyclophosphamide; Topo: topotecan; VNL: vinorelbine

Definition of outcomes

The response were assessed after two, four, and six courses. This study assessed response using RECIST 1.1 criteria [16]. Efficacy of target lesions was defined as: (1) CR: all target lesions disappeared, and pathological lymph nodes reduced to < 10 mm. (2) PR: target lesion diameters reduced by at least 30% from baseline. (3) SD: target lesions did not decrease enough for PR or increase enough for PD, falling between PR and PD. (4) PD: an increase of at least 5 mm and 20% in the total diameter of target lesions compared to the smallest recorded value (or baseline if it’s the smallest), or the emergence of new lesions.

The endpoints were objective response rate (ORR) and disease control rate (DCR) based on bone/bone marrow examination and general imaging examinations such as CT, MRI, or PET. ORR was defined as CR and PR, while DCR was defined as CR, PR, and SD.

Meanwhile, we monitored tumor markers, including serum NSE, VMA/Cr ratio, and LDH, every two chemotherapy courses. In addition, we monitored common adverse events (AEs) after ATO administration, such as myelosuppression, cardiotoxicity, and allergic reactions. According to the criteria of CTCAE 4.03 [17], the adverse effect severity was classified as grades 0, I, II, III, IV, and V, showing a positive correlation between toxicity and grading.

Statistical analysis

Statistical analysis and mapping were performed using GraphPad Prism 9.5 in this study. Testing for normality was performed by Shapiro-Wilk. Then, paired t tests or paired Wilcoxon rank sum tests were used to test significance. A P-value of less than 0.05 is considered significant.

Results

Patients

Between January 2021 and July 2022, 11 eligible patients were enrolled. All patients were classified as high risk on the basis of the the revised neuroblastoma classification by COG in 2021 [15]. Four patients (36.4%) had relapsed HR-NB, and the remainder had refractory disease (n = 7, 63.6%; Table 3). In patients, the primary NB sites were the retroperitoneal space (n = 8, 72.7%) and the mediastinum (n = 3, 27.3%). Of 11 patients < 18 years of age, 5 (45.4%) had MYCN-amplified tumors, 4 (36.4%) had concomitant bone marrow metastases, and all of them had bone metastases (n = 11, 100.0%). Before receiving salvage chemotherapy regimens containing ATO, patients were heavily pre-treated with different regimens, including COG chemotherapy regimen in four (36.4%), ATO combined with conventional chemotherapy regimen in six (54.5%), and CCCG-NB regimen (modified N7 regimen) in three (27.3%).

The disease type, previous chemotherapy strategy, MYCN amplifications, chromosome deletions, and gene sequencing results for all 11 patients are shown in Table 4. Genes commonly associated with poor prognoses in NB, such as MYCN, ALK, RB1, and PIK3CA, were included. In terms of gene type, patients responding to salvage chemotherapy as PD carried genes associated with poor NB prognosis in 75% (3/4) compared with non-PD patients (28.6%, 2/7). Likewise, 50% (2/4) of PD patients had chromosomal deletions compared with 14.3% (1/7) of non-PD patients.

Table 3 Baseline patient characteristics

Parameter	No. of patients (n = 11)	CR + PR + SD	PD	
Age				
 < 18 months	0 (0.0%)	0	0	
 ≥ 18 months	11 (100.0%)	7	4	
Gender				
 Male	8 (72.7%)	5	3	
 Female	3 (27.3%)	2	1	
Relapsed/refractory				
 Relapsed	4 (36.4%)	3	1	
 Refractory	7 (63.6%)	4	3	
Previous chemotherapy strategy				
 Strategy of COG	4 (36.4%)	2	2	
 ATO combined with chemotherapy	4 (36.4%)	3	1	
 CCCG-NB	3 (27.3%)	2	1	
Histologic subtyping				
 Undifferentaited NB	1 (9.1%)	0	1	
 Poorly undifferentaited NB	4 (36.4%)	2	2	
 Well-differentaited NB	1 (9.1%)	1	0	
 Ganglioneuroblastoma, intermixed	4 (36.4%)	3	1	
 Ganglioneuroblastoma, nodular	1 (9.1%)	1	0	
Primary site				
 Retroperitoneal space	8 (72.7%)	5	3	
 Mediastinum	3 (27.3%)	2	1	
Distant metastasis				
 Bone	11 (100.0%)	7	4	
 Bone marrow	4 (36.4%)	10	1	
 Neurocentral nervous system	2 (18.2%)	1	1	
MYCN gene amplification				
 Positive	5 (45.4%)	2	3	
 Negative	3 (27.3%)	2	1	
 Not tested	3 (27.3%)	3	0	
Chromosome deletion				
 Yes	3 (27.3%)	1	2	
 No	0 (0.0%)	0	0	
 Not tested	8 (72.7%)	6	2	
Genes associated with poor prognosis of NB				
 Positive	5 (45.4%)	2	3	
 Negative	4 (36.4%)	4	0	
 Not tested	2 (18.2%)	1	1	
Abbreviations: ATO: arsenic trioxide; CR: complete response; PR: partial response; SD: stable disease; PD: progressive disease; COG: the Children’s Oncology Group; CCCG: Chinese Children’s Cancer Group

Table 4 Disease type, previous chemotherapy strategy, genotypes, and responses of 11 relapsed/refractory patients

Patient ID	Type	Previous chemotherapy strategy	Genotypes	Response	
MYCN gene amplification	Chromosome deletion	Gene sequencing	
1	relapsed	Strategy of COG	-	1p-, 11q-	UK	PR	
2	refractory	ATO combined with chemotherapy (CAV, PVP, CT)	+	UK	PIK3CA, STAT5B	PR	
3	refractory	Strategy of COG	UK	UK	KMT2D, SUZ12	PR	
4	refractory	ATO combined with chemotherapy (CAV, PVP, CT)	-	UK	SMARCA4, KMT2D, NCOR2	PR	
5	refractory	Strategy of COG	UK	UK	-	PR	
6	refractory	Strategy of COG	+	UK	DICER1	PR	
7	relapsed	CCCG-NB	-	UK	CBL, EED, DICER1, MYOD1, RB1	SD	
8	relapsed	ATO combined with chemotherapy (CAV, PVP, CT)	+	1p-, 11q-	NRAS, EGFR	PD	
9	relapsed	CCCG-NB	+	1p-, 11q-	ALK, MDM2, MYCN	PD	
10	refractory	ATO combined with chemotherapy (CAV, PVP, CT)	+	UK	UK	PD	
11	refractory	CCCG-NB	UK	UK	UK	PD	
Abbreviations: COG: Children’s Oncology Group; arsenic trioxide: ATO; CAV: cyclophosphamide/doxorubicin/vincristine; PVP: cisplatin/etoposide; CT: topotecan/cyclophosphamide; CCCG: Chinese Children’s Cancer Group; +: positive; -: negative; UK: unknown; PR: partial response; SD: stable disease; PD: progressive disease

Response

All patients were evaluated for treatment response. A total of 11 patients underwent salvage chemotherapy regimens containing ATO for two to five courses. The ORR of CR and PR using INSS criteria for all eligible patients was 54.5% (6/11), including no CR and six PR (Table 5; Fig. 1). The DCR of CR, PR and SD was 63.6% (7/11), including no CR, six PR, and one SD (Table 5; Fig. 1).

Table 5 Overall response to salvage chemotherapy regimens in patients with relapsed/ refractory NB

Patient	CR	PR	PD	SD	ORR,a No. (%)	DCR,b No.
(%)	
Relapsed

 (n = 4)

	0	2	1	1	54.5	63.6	
Refractory

 (n = 7)

	0	4	3	0	
Abbreviations: CR: complete response; PR: partial response; PD: progressive disease; SD: stable disease

a Overall response rate includes CR and PR

b Overall response rate includes CR, PR and SD

Fig. 1 Overall response to salvage chemotherapy regimens in patients with relapsed (n = 4) or refractory (n = 7) NB

Toxicity

Full-course AEs are shown in Table 6. In total, 11 patients in the safety analysis set reported 56 AEs. There were no treatment-related deaths reported. The most common AEs of the salvage chemotherapy regimens used in this study were grade IV myelosuppression (n = 11) and grade II gastro-intestinal symptoms (n = 11), according to to the criteria of CTCAE 4.03. Remarkably, the next most common AEs were infection and hepatotoxicity (Table 6). Eight (72.7%) patients had secondary infections due to bone myelosuppression and gastrointestinal symptoms, six (54.5%) of which were grade I and two (18.2%) grade II. Nine (81.8%) patients reported grade II hepatotoxicity. Five (45.5%) patients developed grade II diarrhea and grade II cardiac adverse reactions. In addition, three (27.3%) patients reported abdominal pain, including two grade I (18.2%) and one (9.1%) grade II case. Oral mucositis of grade II was observed in three (27.3%) patients. Allergic reactions (grade II) were the least frequent, occurring in only one (9.1%) patient. The AEs above were relieved after symptomatic treatment or gradually disappeared after drug withdrawal.

Table 6 Times of adverse events in full-length salvage chemotherapy containing ATO

Adverse Events	The grade of adverse events, n(%)	
I	II	III	IV	V	
Myelosuppressive	0 (0.0%)	0 (0.0%)	0 (0.0%)	11 (100.0%)	0 (0.0%)	
Infection	6 (54.5%)	2 (18.2%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Nausea and vomiting	0 (0.0%)	11 (100.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Diarrhea	0 (0.0%)	5 (45.5%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Abdominal pain	2 (18.2%)	1 (9.1%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Hepatotoxicity	0 (0.0%)	9 (81.8%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Cadio-toxicity	0 (0.0%)	5 (45.5%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Allergic reaction	0 (0.0%)	1 (9.1%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	
Oral mucositis	0 (0.0%)	3 (27.3%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	

Tumor markers

The serum NSE, 24-h urinary VMA/Cr, and serum LDH levels were evaluated at the initial admission and every disease assessment, as shown in Table 7; Fig. 2. The purpose was to investigate the relationship between NSE, VMA/Cr, and LDH levels in patients with relapsed or refractory HR-NB and the changes before and after the adoption of the salvage chemotherapy regimens containing ATO. The levels of NSE, VMA/Cr, and LDH in patients before and after treatment with this regimen did not exhibit statistically significant changes, with P-values of 0.58, 0.46, and 0.10, respectively.

Table 7 Comparison of serum NSE, 24-h urinary VMA/Cr, and serum LDH levels in children with NB before and after treatment

Group	NSE (ng/mL)	VMA/Cr	LDH (U/L)	
Before treatment	24.90 ± 20.70	15.96 ± 12.23	218.55 ± 205.00	
After treatment	31.85 ± 25.40	17.68 ± 12.00	344.82 ± 264.00	
P value	0.58a	0.46a	0.10a	
a Paired Wilcoxon rank-sum tests

Fig. 2 Variation between serum NSE (A), 24-h urinary VMA/Cr (B) and serum LDH (C) before and after salvage chemotherapy regimens containing ATO in patients with relapsed or refractory HR-NB. ns, P > 0.05

Discussion

Significant advances have been achieved in clinical treatment strategies as a result of comprehensive investigations into the biological characteristics and pathogenesis of NB. However, despite the implementation of multiple treatments within a multidisciplinary combined diagnostic model, HR-NB remains susceptible to recurrence or progression among patients. This phenomenon significantly impacts the prognosis of affected children, leading to suboptimal long-term survival outcomes. The emergence of MDR and minimal residual disease (MRD) during the advanced stages of chemotherapy diminishes the effectiveness of hematopoietic stem cell transplantation (HSCT) and immunotherapy, resulting in a relapse rate of up to 80% within a span of two years [18]. Despite the numerous advances in the treatment of NB, the persistence of relapsed or refractory disease continues to pose a significant barrier to achieving a cure. The chemotherapy combinations administered to patients with relapsed or refractory NB are typically different from those initially employed. Fiona Herd et al. [19] provided a comprehensive summary of different salvage regimens and their respective ORR, which included CT with a response rate of 63%, CTE with a response rate of 61%, and CTV with a response rate of 52%. Recent research also indicate that patients diagnosed with relapsed or refractory NB may derive advantages from intensified therapeutic interventions aimed at attaining a comprehensive remission, subsequently followed by consolidation therapy, such as HSCT, which leads to a sustained remission or complete eradication of the ailment [20]. Thus, we attempted to combine ATO with a more efficacious salvage chemotherapy regimen, with the aim of enhancing the overall outcome and prognosis for patients afflicted with relapsed or refractory NB. Here we present the anti-tumor and safety activity of the ATO combined salvage chemotherapy regimens in children with relapsed or refractory NB. In this study, the primary aims were to evaluate the anti-tumor activity of these modified salvage chemotherapy regimens by determining the ORR and DCR. Secondary aims were to determined the safety and toxicity of salvage chemotherapy regimens containing ATO by the incidence of AEs.

Our results indicate that salvage chemotherapy regimens containing ATO are both efficacious and well tolerated in patients with relapsed or refractory HR-NB. From an efficacy standpoint, out of the 11 patients included in our study who had relapsed or refractory conditions, 7 experienced PR or maintained SD, while the remaining 4 unfortunately experienced PD. The ORR among patients who underwent relapsed or refractory chemotherapy was slightly lower (54.5% vs. 52.0-63.0%) than reported in existing research [21–24]. Theoretically, salvage chemotherapy regimens containing ATO would be a promising treatment option for patients with relapsed or refractory NB. On one hand, we speculated that all 11 patients recruited in this study were treated with multiple second-line chemotherapy regimens and may have developed MDR to salvage chemotherapy regimens. The mechanisms underlying resistance in NB cells are intricate and diverse, encompassing factors such as tumor load and growth kinetics, tumor heterogeneity, incurable cancer drivers, the immune system, and physical barriers [7]. The up-regulation of ATP-binding cassette transporters, namely P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance protein 1 (MRP1), has been demonstrated to enhance drug efflux, which serves as a significant resistance mechanism in HR-NB [25, 26]. On the other hand, previous research on relapsed or refractory NB has incorporated notably smaller proportions of patients with MYCN amplification, specifically 27.3% [23], 20.0% [22], and 33% [24]. In contrast, the patients included in this study exhibited a higher rate of bone metastasis (100%) and MYCN amplification (45.4%), which are significantly higher than the population characteristics of similar studies. Bone is the most common site of NB metastasis and recurrence, and studies have shown that NB patients with bone metastases respond poorly to chemotherapy and have a poorer prognosis [27, 28]. MYCN amplification is widely recognized as the predominant genetic modification in HR-NB, and its etiology involves the abnormal activation of the PI3K/AKT/mTOR pathway, resulting in the excessive expression of the MYCN protein, indicating an unfavorable prognosis [29]. Furthermore, this study revealed that genes linked to unfavorable prognosis, such as ALK, MYCN, EGFR, and CHD6, were detected in 55.6% (n = 5) of the nine patients who underwent gene sequencing, surpassing the prevalence reported in the Ashraf study (26%) [23]. This study reveals that patients who received ATO in combination with salvage chemotherapy exhibited notable rates of ORR (54.5%) and DCR (63.6%), thereby reinforcing the significance of ATO in the treatment of HR-NB patients. However, it was observed that there was no significant decrease in the relevant tumor markers of the patients following treatment. This observation indicates that children with relapsed or refractory NB encounter significant challenges in attaining CR. This difficulty may be attributable to the persistence of central lesions in some patients, which impede the efficacy of pharmacological treatments by obstructing drug passage through the blood-brain barrier [30]. Additionally, it is important to note that the sample size of this cohort was insufficient, leading to considerable variability and fluctuations in the overall data. Simultaneously, it is encouraging to note that the systemic toxicity of chemotherapy observed in all participants of our study exhibited a resemblance to previous research, primarily characterized by prevalent myelosuppression and gastrointestinal symptoms, while the remaining AEs were predominantly mild. This finding demonstrates a notable similarity to the toxicities commonly associated with traditional chemotherapy treatment protocols.

In general, the utilization of the ATO-based chemotherapy salvage regimen exhibits the potential to extend the duration of disease stabilization in patients diagnosed with relapsed or refractory HR-NB, demonstrating favorable effectiveness and safety. Consequently, this treatment approach warrants further consideration for widespread implementation in clinical practice. Nevertheless, it is important to acknowledge certain limitations within our study, notably the inclusion of a relatively small cohort of relapsed refractory NB patients. Overall, the ATO-based chemotherapy salvage regimen can prolong the time of disease stabilization in patients with relapsed-refractory HR-NB with good efficacy and safety, which is worthy of further promotion in clinical treatment. However, there are some limitations in our study, such as the number of relapsed refractory NB patients included in this study being too small. In the next step, we will try to expand the study time frame to recruit as many eligible patients as possible, and we will also encourage other centers to join us. We look forward to more teams joining our ATO clinical study in the future and contributing to the cure of more patients with relapsed or refractory NB.

Acknowledgements

Not applicable.

Author contributions

Conceptualization: Yang Li; Methodology: Yang Li, Xiaoshan Liu, Xiaomin Peng; Writing—original draft: Xiaoshan Liu, Xiaomin Peng; Writing—review and editing: Yang Li; Data curation: Xiaomin Peng, Shu Yang, Xiaoshan Liu, Yuhan Ma, Yu Wu, Zhixuan Wang; Formal analysis: Xiaoshan Liu; Visualization: Xiaoshan Liu, Xiaomin Peng; Supervision: Wenjun Weng; Validation: Haijin Liu, Shouhua Zhang, Jinhu Wang; Project administration: Yang Li; Funding acquisition: Yang Li.

Funding

This work was supported by the Guangzhou Area Clinical Specialty Technology Program (Grant 2023P-TS39), the Sun Yat-Sen Medical–Industrial Integration Cultivating Program (Grant YXYGRH202203), and Heilongjiang Harbin Yida Pharmaceutical Co. (Grant 7670020013).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

The Ethics Committee of Sun Yet-sen Memorial hospital of Sun Yat-sen University (China, Guangzhou) approved this study (ID SYSKY-2023-678-01). All individual patients provided informed written consent to participate in this study. This study was performed in accordance with the Declaration of Helsinki.

Competing interests

The authors declare no competing interests.

Abbreviations

AEs Adverse events

ATO Arsenic trioxide

CAV Cyclophosphamide, doxorubicin and vincristine

CCCG Chinese Children’s Cancer Group

COG The Children’s Oncology Group

CR Complete response

CT Computed tomography

CTE Cyclophosphamide, topotecan, and etoposide

CTX Cyclophosphamide

DCR Disease control rate

HR-NB High-risk neuroblastoma

HSCT Hematopoietic stem cell transplantation

ICE Ifosfamide, carboplatin, and etoposide

INSS International Neuroblastoma Staging System

LDH Lactate dehydrogenase

MDR Multidrug resistance

MRD Minimal residual disease

MRI Magnetic resonance imaging

NB Neuroblastoma

NSE Neuron-specific enolase

ORR Objective response rate

PD Progressive disease

PET Positron emission tomography

PR Partial response

PVP Cisplatin and etoposide

SD Stable disease

TC Topotecan and cyclophosphamide

Topo Topotecan

TOTEM Temozolomide and topotecan

TVC Topotecan, vincristine and cyclophosphamide

TVD Topotecan, vincristine and doxorubicin

VCR Vincristine

VMA/Cr Vanillylmandelic acid/creatinine

VNL Vinorelbine

VP-16 Etoposide

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Xiaoshan Liu and Xiaomin Peng contributed equally to this work.
==== Refs
References

1. Matthay KK Maris JM Schleiermacher G Nakagawara A Mackall CL Diller L Weiss WA Neuroblastoma Nat Rev Dis Primers 2016 2 16078 10.1038/nrdp.2016.78 27830764
Matthay KK, Maris JM, Schleiermacher G, Nakagawara A, Mackall CL, Diller L, Weiss WA. Neuroblastoma. Nat Rev Dis Primers. 2016;2:16078.27830764 10.1038/nrdp.2016.78
2. Qiu B Matthay KK Advancing therapy for neuroblastoma Nat Rev Clin Oncol 2022 19 8 515 33 10.1038/s41571-022-00643-z 35614230
Qiu B, Matthay KK. Advancing therapy for neuroblastoma. Nat Rev Clin Oncol. 2022;19(8):515–33.35614230 10.1038/s41571-022-00643-z
3. Zeineldin M Patel AG Dyer MA Neuroblastoma: when differentiation goes awry Neuron 2022 110 18 2916 28 10.1016/j.neuron.2022.07.012 35985323
Zeineldin M, Patel AG, Dyer MA. Neuroblastoma: when differentiation goes awry. Neuron. 2022;110(18):2916–28.35985323 10.1016/j.neuron.2022.07.012
4. Monclair T Brodeur GM Ambros PF Brisse HJ Cecchetto G Holmes K Kaneko M London WB Matthay KK Nuchtern JG von Schweinitz D Simon T Cohn SL Pearson AD INRG Task Force. The International Neuroblastoma Risk Group (INRG) staging system: an INRG Task Force report J Clin Oncol 2009 27 2 298 303 10.1200/JCO.2008.16.6876 19047290
Monclair T, Brodeur GM, Ambros PF, Brisse HJ, Cecchetto G, Holmes K, Kaneko M, London WB, Matthay KK, Nuchtern JG, von Schweinitz D, Simon T, Cohn SL, Pearson AD, INRG Task Force. The International Neuroblastoma Risk Group (INRG) staging system: an INRG Task Force report. J Clin Oncol. 2009;27(2):298–303.19047290 10.1200/JCO.2008.16.6876
5. Tan AC Ashley DM López GY Malinzak M Friedman HS Khasraw M Management of glioblastoma: state of the art and future directions CA Cancer J Clin 2020 70 4 299 312 10.3322/caac.21613 32478924
Tan AC, Ashley DM, López GY, Malinzak M, Friedman HS, Khasraw M. Management of glioblastoma: state of the art and future directions. CA Cancer J Clin. 2020;70(4):299–312.32478924 10.3322/caac.21613
6. Lau DT Hesson LB Norris MD Marshall GM Haber M Ashton LJ Prognostic significance of promoter DNA methylation in patients with childhood neuroblastoma Clin Cancer Res 2012 18 20 5690 700 10.1158/1078-0432.CCR-12-0294 22929802
Lau DT, Hesson LB, Norris MD, Marshall GM, Haber M, Ashton LJ. Prognostic significance of promoter DNA methylation in patients with childhood neuroblastoma. Clin Cancer Res. 2012;18(20):5690–700.22929802 10.1158/1078-0432.CCR-12-0294
7. Vasan N Baselga J Hyman DM A view on drug resistance in cancer Nature 2019 575 7782 299 309 10.1038/s41586-019-1730-1 31723286
Vasan N, Baselga J, Hyman DM. A view on drug resistance in cancer. Nature. 2019;575(7782):299–309.31723286 10.1038/s41586-019-1730-1
8. Zafar A Wang W Liu G Wang X Xian W McKeon F Foster J Zhou J Zhang R Molecular targeting therapies for neuroblastoma: Progress and challenges Med Res Rev 2021 41 2 961 1021 10.1002/med.21750 33155698
Zafar A, Wang W, Liu G, Wang X, Xian W, McKeon F, Foster J, Zhou J, Zhang R. Molecular targeting therapies for neuroblastoma: progress and challenges. Med Res Rev. 2021;41(2):961–1021.33155698 10.1002/med.21750
9. Chung C Boterberg T Lucas J Panoff J Valteau-Couanet D Hero B Bagatell R Hill-Kayser CE Neuroblastoma Pediatr Blood Cancer 2021 68 Suppl 2 e28473 10.1002/pbc.28473 33818884
Chung C, Boterberg T, Lucas J, Panoff J, Valteau-Couanet D, Hero B, Bagatell R, Hill-Kayser CE. Neuroblastoma. Pediatr Blood Cancer. 2021;68(Suppl 2):e28473.33818884 10.1002/pbc.28473
10. Qi K Li Y Huang K Xiong X Chuchu F Zhang C Weng W Pre-application of arsenic trioxide may potentiate cytotoxic effects of vinorelbine/docetaxel on neuroblastoma SK-N-SH cells Biomed Pharmacother 2019 113 108665 10.1016/j.biopha.2019.108665 30889490
Qi K, Li Y, Huang K, Xiong X, Chuchu F, Zhang C, Weng W. Pre-application of arsenic trioxide may potentiate cytotoxic effects of vinorelbine/docetaxel on neuroblastoma SK-N-SH cells. Biomed Pharmacother. 2019;113:108665.30889490 10.1016/j.biopha.2019.108665
11. Liu L Li Y Xiong X Qi K Zhang C Fang J Guo H Low dose of arsenic trioxide inhibits multidrug resistant-related P-glycoprotein expression in human neuroblastoma cell line Int J Oncol 2016 49 6 2319 30 10.3892/ijo.2016.3756 27840903
Liu L, Li Y, Xiong X, Qi K, Zhang C, Fang J, Guo H. Low dose of arsenic trioxide inhibits multidrug resistant-related P-glycoprotein expression in human neuroblastoma cell line. Int J Oncol. 2016;49(6):2319–30.27840903 10.3892/ijo.2016.3756
12. Chen S Wu JL Liang Y Tang YG Song HX Wu LL Xing YF Yan N Li YT Wang ZY Xiao SJ Lu X Chen SJ Lu M Arsenic Trioxide rescues structural p53 mutations through a cryptic allosteric site Cancer Cell 2021 39 2 225 e2398 10.1016/j.ccell.2020.11.013 33357454
Chen S, Wu JL, Liang Y, Tang YG, Song HX, Wu LL, Xing YF, Yan N, Li YT, Wang ZY, Xiao SJ, Lu X, Chen SJ, Lu M. Arsenic trioxide rescues structural p53 mutations through a cryptic allosteric site. Cancer Cell. 2021;39(2):225–e2398.33357454 10.1016/j.ccell.2020.11.013
13. Li C Peng X Feng C Xiong X Li J Liao N Yang Z Liu A Wu P Liang X He Y Tian X Lin Y Wang S Li Y Excellent early outcomes of combined Chemotherapy with Arsenic Trioxide for Stage 4/M neuroblastoma in children: a Multicenter Nonrandomized Controlled Trial Oncol Res 2021 28 7 791 800 10.3727/096504021X16184815905096 33858561
Li C, Peng X, Feng C, Xiong X, Li J, Liao N, Yang Z, Liu A, Wu P, Liang X, He Y, Tian X, Lin Y, Wang S, Li Y. Excellent early outcomes of combined chemotherapy with arsenic trioxide for stage 4/M neuroblastoma in children: a multicenter nonrandomized controlled trial. Oncol Res. 2021;28(7):791–800.33858561 10.3727/096504021X16184815905096
14. Li Y Feng C Chen Y Huang K Li C Xiong X Li P Zhou D Peng X Weng W Deng X Wu Y Fang J Improved outcomes with induction chemotherapy combined with Arsenic Trioxide in Stage 4 Neuroblastoma: a Case Series Technol Cancer Res Treat 2021 20 15330338211041454 10.1177/15330338211041454 34569870
Li Y, Feng C, Chen Y, Huang K, Li C, Xiong X, Li P, Zhou D, Peng X, Weng W, Deng X, Wu Y, Fang J. Improved outcomes with induction chemotherapy combined with arsenic trioxide in stage 4 neuroblastoma: a case series. Technol Cancer Res Treat. 2021;20:15330338211041454.34569870 10.1177/15330338211041454
15. Irwin MS Naranjo A Zhang FF Cohn SL London WB Gastier-Foster JM Ramirez NC Pfau R Reshmi S Wagner E Nuchtern J Asgharzadeh S Shimada H Maris JM Bagatell R Park JR Hogarty MD Revised neuroblastoma risk classification system: a Report from the children’s Oncology Group J Clin Oncol 2021 39 29 3229 41 10.1200/JCO.21.00278 34319759
Irwin MS, Naranjo A, Zhang FF, Cohn SL, London WB, Gastier-Foster JM, Ramirez NC, Pfau R, Reshmi S, Wagner E, Nuchtern J, Asgharzadeh S, Shimada H, Maris JM, Bagatell R, Park JR, Hogarty MD. Revised neuroblastoma risk classification system: a report from the children’s oncology group. J Clin Oncol. 2021;39(29):3229–41.34319759 10.1200/JCO.21.00278
16. Eisenhauer EA Therasse P Bogaerts J Schwartz LH Sargent D Ford R Dancey J Arbuck S Gwyther S Mooney M Rubinstein L Shankar L Dodd L Kaplan R Lacombe D Verweij J New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1) Eur J Cancer 2009 45 2 228 47 10.1016/j.ejca.2008.10.026 19097774
Eisenhauer EA, Therasse P, Bogaerts J, Schwartz LH, Sargent D, Ford R, Dancey J, Arbuck S, Gwyther S, Mooney M, Rubinstein L, Shankar L, Dodd L, Kaplan R, Lacombe D, Verweij J. New response evaluation criteria in solid tumours: revised RECIST guideline (version 1.1). Eur J Cancer. 2009;45(2):228–47.19097774 10.1016/j.ejca.2008.10.026
17. US Department of Health and Human Services Common terminology criteria for adverse events (CTCAE) Version 4.03 2010 Bethesda, MD National Institutes of Health
US Department of Health and Human Services. Common terminology criteria for adverse events (CTCAE) Version 4.03. Bethesda, MD: National Institutes of Health; 2010.
18. Basta NO Halliday GC Makin G Birch J Feltbower R Bown N Elliott M Moreno L Barone G Pearson AD James PW Tweddle DA McNally RJ Factors associated with recurrence and survival length following relapse in patients with neuroblastoma Br J Cancer 2016 115 9 1048 57 10.1038/bjc.2016.302 27701387
Basta NO, Halliday GC, Makin G, Birch J, Feltbower R, Bown N, Elliott M, Moreno L, Barone G, Pearson AD, James PW, Tweddle DA, McNally RJ. Factors associated with recurrence and survival length following relapse in patients with neuroblastoma. Br J Cancer. 2016;115(9):1048–57.27701387 10.1038/bjc.2016.302
19. Herd F Basta NO McNally RJQ Tweddle DA A systematic review of re-induction chemotherapy for children with relapsed high-risk neuroblastoma Eur J Cancer 2019 111 50 8 10.1016/j.ejca.2018.12.032 30822684
Herd F, Basta NO, McNally RJQ, Tweddle DA. A systematic review of re-induction chemotherapy for children with relapsed high-risk neuroblastoma. Eur J Cancer. 2019;111:50–8.30822684 10.1016/j.ejca.2018.12.032
20. Zage PE Novel therapies for relapsed and refractory neuroblastoma Child (Basel) 2018 5 11 148
Zage PE. Novel therapies for relapsed and refractory neuroblastoma. Child (Basel). 2018;5(11):148.
21. Kushner BH Kramer K Modak S Qin LX Cheung NK Differential impact of high-dose cyclophosphamide, topotecan, and vincristine in clinical subsets of patients with chemoresistant neuroblastoma Cancer 2010 116 12 3054 60 10.1002/cncr.25232 20564411
Kushner BH, Kramer K, Modak S, Qin LX, Cheung NK. Differential impact of high-dose cyclophosphamide, topotecan, and vincristine in clinical subsets of patients with chemoresistant neuroblastoma. Cancer. 2010;116(12):3054–60.20564411 10.1002/cncr.25232
22. Garaventa A Luksch R Biasotti S Severi G Pizzitola MR Viscardi E Prete A Mastrangelo S Podda M Haupt R De Bernardi B A phase II study of topotecan with vincristine and doxorubicin in children with recurrent/refractory neuroblastoma Cancer 2003 98 11 2488 94 10.1002/cncr.11797 14635085
Garaventa A, Luksch R, Biasotti S, Severi G, Pizzitola MR, Viscardi E, Prete A, Mastrangelo S, Podda M, Haupt R, De Bernardi B. A phase II study of topotecan with vincristine and doxorubicin in children with recurrent/refractory neuroblastoma. Cancer. 2003;98(11):2488–94.14635085 10.1002/cncr.11797
23. Ashraf K Shaikh F Gibson P Baruchel S Irwin MS Treatment with topotecan plus cyclophosphamide in children with first relapse of neuroblastoma Pediatr Blood Cancer 2013 60 10 1636 41 10.1002/pbc.24587 23650219
Ashraf K, Shaikh F, Gibson P, Baruchel S, Irwin MS. Treatment with topotecan plus cyclophosphamide in children with first relapse of neuroblastoma. Pediatr Blood Cancer. 2013t;60(10):1636–41.23650219 10.1002/pbc.24587
24. Simon T Längler A Harnischmacher U Frühwald MC Jorch N Claviez A Berthold F Hero B Topotecan, cyclophosphamide, and etoposide (TCE) in the treatment of high-risk neuroblastoma. Results of a phase-II trial J Cancer Res Clin Oncol 2007 133 9 653 61 10.1007/s00432-007-0216-y 17479288
Simon T, Längler A, Harnischmacher U, Frühwald MC, Jorch N, Claviez A, Berthold F, Hero B. Topotecan, cyclophosphamide, and etoposide (TCE) in the treatment of high-risk neuroblastoma. Results of a phase-II trial. J Cancer Res Clin Oncol. 2007;133(9):653–61.17479288 10.1007/s00432-007-0216-y
25. Kobayashi M Mizutani A Nishi K Muranaka Y Nishii R Shikano N Nakanishi T Tamai I Kleinerman ES Kawai K [131I]MIBG exports via MRP transporters and inhibition of the MRP transporters improves accumulation of [131I]MIBG in neuroblastoma Nucl Med Biol 2020 90–91 49 54 10.1016/j.nucmedbio.2020.09.004 33032192
Kobayashi M, Mizutani A, Nishi K, Muranaka Y, Nishii R, Shikano N, Nakanishi T, Tamai I, Kleinerman ES, Kawai K. [131I]MIBG exports via MRP transporters and inhibition of the MRP transporters improves accumulation of [131I]MIBG in neuroblastoma. Nucl Med Biol. 2020;90–91:49–54.33032192 10.1016/j.nucmedbio.2020.09.004
26. Calvet L Santos A Valent A Terrier-Lacombe MJ Opolon P Merlin JL Aubert G Morizet J Schellens JH Bénard J Vassal G No topoisomerase I alteration in a neuroblastoma model with in vivo acquired resistance to irinotecan Br J Cancer 2004 91 6 1205 12 10.1038/sj.bjc.6602079 15292932
Calvet L, Santos A, Valent A, Terrier-Lacombe MJ, Opolon P, Merlin JL, Aubert G, Morizet J, Schellens JH, Bénard J, Vassal G. No topoisomerase I alteration in a neuroblastoma model with in vivo acquired resistance to irinotecan. Br J Cancer. 2004;91(6):1205–12.15292932 10.1038/sj.bjc.6602079
27. Lin KS Uemura S Thwin KKM Nakatani N Ishida T Yamamoto N Tamura A Saito A Mori T Hasegawa D Kosaka Y Nino N Nagano C Takafuji S Iijima K Nishimura N Minimal residual disease in high-risk neuroblastoma shows a dynamic and disease burden-dependent correlation between bone marrow and peripheral blood Transl Oncol 2021 14 8 101019 10.1016/j.tranon.2021.101019 33993097
Lin KS, Uemura S, Thwin KKM, Nakatani N, Ishida T, Yamamoto N, Tamura A, Saito A, Mori T, Hasegawa D, Kosaka Y, Nino N, Nagano C, Takafuji S, Iijima K, Nishimura N. Minimal residual disease in high-risk neuroblastoma shows a dynamic and disease burden-dependent correlation between bone marrow and peripheral blood. Transl Oncol. 2021;14(8):101019.33993097 10.1016/j.tranon.2021.101019
28. He B Mao J Huang L Clinical characteristics and survival outcomes in Neuroblastoma with Bone Metastasis based on SEER Database Analysis Front Oncol 2021 11 677023 10.3389/fonc.2021.677023 34141621
He B, Mao J, Huang L. Clinical characteristics and survival outcomes in neuroblastoma with bone metastasis based on SEER database analysis. Front Oncol. 2021;11:677023.34141621 10.3389/fonc.2021.677023
29. Campbell K Shyr D Bagatell R Fischer M Nakagawara A Nieto AC Brodeur GM Matthay KK London WB DuBois SG Comprehensive evaluation of context dependence of the prognostic impact of MYCN amplification in neuroblastoma: a report from the International Neuroblastoma Risk Group (INRG) project Pediatr Blood Cancer 2019 66 8 e27819 10.1002/pbc.27819 31115156
Campbell K, Shyr D, Bagatell R, Fischer M, Nakagawara A, Nieto AC, Brodeur GM, Matthay KK, London WB, DuBois SG. Comprehensive evaluation of context dependence of the prognostic impact of MYCN amplification in neuroblastoma: a report from the International Neuroblastoma Risk Group (INRG) project. Pediatr Blood Cancer. 2019;66(8):e27819.31115156 10.1002/pbc.27819
30. You H Baluszek S Kaminska B Supportive roles of brain macrophages in CNS metastases and assessment of new approaches targeting their functions Theranostics 2020 10 7 2949 64 10.7150/thno.40783 32194848
You H, Baluszek S, Kaminska B. Supportive roles of brain macrophages in CNS metastases and assessment of new approaches targeting their functions. Theranostics. 2020;10(7):2949–64.32194848 10.7150/thno.40783
