The Phenomenon of Halted Neural Development: Our Current Understanding of Neuroblastoma
Kevin Cho
BACKGROUND
Neuroblastoma is one of the leading causes of cancer in children (Bartolucci et al., 2022). Researchers indicate that the cancer originates from the improper differentiation of neural crest cell precursors of the peripheral nervous system (Zeineldin et al., 2022; Ponzoni et al., 2022). More specifically, these neural crest cells normally migrate out upon the folding of the ectodermal neural tube during embryogenesis to form various structures such as the cranial skeleton, smooth muscle, or sympathetic neurons (Zeineldin et al., 2022). The eventual identity of these initial embryonic neural crest cells depends on their rostro-caudal position along the embryo (Zeineldin et al., 2022). Researchers indicate that neuroblastoma arises from neural crest cells in the trunk region specifically, which normally gives rise to cells of the adrenal medulla, sympathetic neurons, and various other cell types (Jiang et al., 2011; Zeineldin et al., 2022). In line with its developmental origin of immature neural crest cells, neuroblastomas can be found throughout the sympathetic nervous system, although it is most often found in the adrenal medulla found interior to the adrenal gland (Maris, 2010).
Interestingly, the disease significantly varies in severity across cases. While in some instances the tumor can simply regress on its own, high-risk metastatic (in which case the tumor has spread out from its origin) neuroblastoma patients have a below-50% overall survival rate (Tsubota & Kadomatsu, 2017; Qiu & Matthay 2022; Pastorino et al., 2023). In fact, neuroblastoma is responsible for 12-15% of total pediatric cancer deaths, indicating the potential severity of the disease despite its widely varying clinical presentations (Otte et al., 2021). In particular, the INRG (International Neuroblastoma Risk Group) stratifies various neuroblastoma cases as either low-risk, medium-risk, or high-risk according to the stage of the tumor, age at diagnosis, and various genetic risk factors (including amplification of the MYCN gene, a critical genetic risk factor discussed later in this article) (Arendonk & Chung, 2019; Qiu & Matthay, 2022). High-risk neuroblastoma is especially deadly due to the high rate of disease relapse (~50% for high-risk patients), making commonly effective treatments difficult (Pastorino et al., 2023). Notably, recurrent neuroblastoma patients have a survival rate of below 10% (Zeineldin et al., 2022). In contrast, however, low and intermediate-risk neuroblastoma patients have a survival rate of 85-90% (Otte et al., 2021).
RISK FACTORS
Neuroblastomas can feature a wide variety of genetic markers and risk factors, some of which will be discussed here (Qiu & Matthay, 2022). Familial neuroblastomas are often characterized by activation of ALK or inactivation of PHOX2B, both of which are genes involved in sympathoadrenal development (Qiu & Matthay, 2022). Chromosomal mutations are also especially common in neuroblastoma patients, with loss of 1p or 6q most often seen in relapses—possibly due to the loss of tumor suppressor genes like the tumor suppressor ARID1A on the 1p arm (Qiu & Matthay, 2022). Telomere maintenance to permit more cell proliferation through the upregulation of TERT (which encodes telomerase) or through alternative lengthening mechanisms is also common in high-risk patients (Qiu & Matthay, 2022; Cesare & Reddel et al., 2010). Other risk features include mutations in the RAS-MAPK and p53 pathways, which are common in cancer and control processes such as cell death, proliferation, and cell cycle maintenance (Lahalle et al., 2021; Bahar et al., 2023). Amplification of the gene MYCN is also a major risk factor for neuroblastoma; in fact, this feature alone identifies the case as high-risk (Qiu & Matthay, 2022; Arendonk & Chung, 2019). Researchers have established that MYCN is an oncogene (where mutation of the gene drives cancer development) which is primarily responsible for promoting pluripotency to maintain an undifferentiated state—a feature associated with cancer (Huang & Weiss et al., 2013; Zeineldin et al., 2022). In alignment with this, deletion of MYCN in mouse neural precursor cells was found to significantly reduce brain size and promote greater neuronal differentiation—demonstrating the effects of MYCN in inhibiting differentiation (Huang & Weiss et al., 2013). To accomplish these effects, MYCN is involved in the regulation of a number of critical genes, activating those involved in metastasis, proliferation, and tumor development while repressing others involved in differentiation or immune system recognition (Huang & Weiss et al., 2013). Notably, MYCN amplification has never been observed to manifest throughout disease progression in low-risk neuroblastoma patients, indicating that amplification of MYCN is an early critical feature driving high-risk neuroblastoma (Huang & Weiss et al., 2013; Qiu & Matthay, 2022; Arendonk & Chung, 2019; Otte et. al, 2021).
HETEROGENEITY OF NEUROBLASTOMA
Despite limited resources at the time, researchers had already determined that neuroblastoma was composed of at least 2 distinct cellular populations by the 1980s: neuronal (N-type) cells, characterized by their neuronal phenotype along with their release of neurotransmitters, as well as substrate adhesive (S-type) cells, which produce collagen and fibronectin (both supporting proteins involved in the extracellular matrix) (Zeineldin et al., 2022; To & Midwood, 2011). Researchers later re-termed these populations as ADRN and MES-type cells respectively with subsequent analyses, and further characterized their unique gene expression signatures (van Groningen et al., 2017; Zeineldin et al., 2022).
CURRENT TREATMENTS
Current treatment methods vary depending on the severity of the tumor (Jiang et al., 2011). Low-risk neuroblastoma treatment is typically treated with surgery alone, while high-risk neuroblastoma still does not have a definitive cure as the five-year overall survival rate is still ~60% even with modern therapies (Krystal & Foster, 2023). The treatment regimen for high-risk neuroblastoma is multimodal, involving initial chemotherapy and surgery to remove the visible tumor followed by more chemotherapy and radiation in the consolidation phase to account for any remaining components of the disease (Krystal & Foster, 2023; Bartolucci et al., 2022). To buffer for the high dose of chemotherapy, autologous stem cell transplantation (ASCT) is also conducted in the consolidation phase involving collecting stem cells from the patient for later transplantation after chemotherapy (Krystal & Foster, 2023; Bartolucci et al., 2022). Finally, the subsequent maintenance phase involves anti-GD2 immunotherapy—targeting the GD2 antigen often expressed in neuroblastoma—as well as isotretinoin treatment, which promotes differentiation and halting of proliferation in neuroblastoma (Bartolucci et al., 2022). In particular, researchers have demonstrated that ATRA (all-trans retinoic acid, the metabolite of isotretinoin) treatment of MYCN-amplified neuroblastoma reduced growth and promoted neuronal differentiation (Zimmerman et al., 2021). MES-type neuroblastoma cells, however, are particularly problematic for many of these current treatments; researchers indicate that these cells are more resistant to chemotherapy, RA, anti-GD2 immunotherapy, and various drugs (Zeineldin et al., 2022; van Groningen et al., 2017). This is especially an issue as surviving MES-type cells can interconvert to ADRN-type cells, thus renewing the tumor (Zeineldin et al., 2022). Ultimately, researchers suggest that targeting these problematic MES-type neuroblastoma cells may be a promising avenue for new research in paving the way towards a cure (Zeineldin et al., 2022; van Groningen et al., 2017).
About the Author
Kevin Cho (‘26) is a junior at Harvard College concentrating in neuroscience.
References
Neuroblastoma is one of the leading causes of cancer in children (Bartolucci et al., 2022). Researchers indicate that the cancer originates from the improper differentiation of neural crest cell precursors of the peripheral nervous system (Zeineldin et al., 2022; Ponzoni et al., 2022). More specifically, these neural crest cells normally migrate out upon the folding of the ectodermal neural tube during embryogenesis to form various structures such as the cranial skeleton, smooth muscle, or sympathetic neurons (Zeineldin et al., 2022). The eventual identity of these initial embryonic neural crest cells depends on their rostro-caudal position along the embryo (Zeineldin et al., 2022). Researchers indicate that neuroblastoma arises from neural crest cells in the trunk region specifically, which normally gives rise to cells of the adrenal medulla, sympathetic neurons, and various other cell types (Jiang et al., 2011; Zeineldin et al., 2022). In line with its developmental origin of immature neural crest cells, neuroblastomas can be found throughout the sympathetic nervous system, although it is most often found in the adrenal medulla found interior to the adrenal gland (Maris, 2010).
Interestingly, the disease significantly varies in severity across cases. While in some instances the tumor can simply regress on its own, high-risk metastatic (in which case the tumor has spread out from its origin) neuroblastoma patients have a below-50% overall survival rate (Tsubota & Kadomatsu, 2017; Qiu & Matthay 2022; Pastorino et al., 2023). In fact, neuroblastoma is responsible for 12-15% of total pediatric cancer deaths, indicating the potential severity of the disease despite its widely varying clinical presentations (Otte et al., 2021). In particular, the INRG (International Neuroblastoma Risk Group) stratifies various neuroblastoma cases as either low-risk, medium-risk, or high-risk according to the stage of the tumor, age at diagnosis, and various genetic risk factors (including amplification of the MYCN gene, a critical genetic risk factor discussed later in this article) (Arendonk & Chung, 2019; Qiu & Matthay, 2022). High-risk neuroblastoma is especially deadly due to the high rate of disease relapse (~50% for high-risk patients), making commonly effective treatments difficult (Pastorino et al., 2023). Notably, recurrent neuroblastoma patients have a survival rate of below 10% (Zeineldin et al., 2022). In contrast, however, low and intermediate-risk neuroblastoma patients have a survival rate of 85-90% (Otte et al., 2021).
RISK FACTORS
Neuroblastomas can feature a wide variety of genetic markers and risk factors, some of which will be discussed here (Qiu & Matthay, 2022). Familial neuroblastomas are often characterized by activation of ALK or inactivation of PHOX2B, both of which are genes involved in sympathoadrenal development (Qiu & Matthay, 2022). Chromosomal mutations are also especially common in neuroblastoma patients, with loss of 1p or 6q most often seen in relapses—possibly due to the loss of tumor suppressor genes like the tumor suppressor ARID1A on the 1p arm (Qiu & Matthay, 2022). Telomere maintenance to permit more cell proliferation through the upregulation of TERT (which encodes telomerase) or through alternative lengthening mechanisms is also common in high-risk patients (Qiu & Matthay, 2022; Cesare & Reddel et al., 2010). Other risk features include mutations in the RAS-MAPK and p53 pathways, which are common in cancer and control processes such as cell death, proliferation, and cell cycle maintenance (Lahalle et al., 2021; Bahar et al., 2023). Amplification of the gene MYCN is also a major risk factor for neuroblastoma; in fact, this feature alone identifies the case as high-risk (Qiu & Matthay, 2022; Arendonk & Chung, 2019). Researchers have established that MYCN is an oncogene (where mutation of the gene drives cancer development) which is primarily responsible for promoting pluripotency to maintain an undifferentiated state—a feature associated with cancer (Huang & Weiss et al., 2013; Zeineldin et al., 2022). In alignment with this, deletion of MYCN in mouse neural precursor cells was found to significantly reduce brain size and promote greater neuronal differentiation—demonstrating the effects of MYCN in inhibiting differentiation (Huang & Weiss et al., 2013). To accomplish these effects, MYCN is involved in the regulation of a number of critical genes, activating those involved in metastasis, proliferation, and tumor development while repressing others involved in differentiation or immune system recognition (Huang & Weiss et al., 2013). Notably, MYCN amplification has never been observed to manifest throughout disease progression in low-risk neuroblastoma patients, indicating that amplification of MYCN is an early critical feature driving high-risk neuroblastoma (Huang & Weiss et al., 2013; Qiu & Matthay, 2022; Arendonk & Chung, 2019; Otte et. al, 2021).
HETEROGENEITY OF NEUROBLASTOMA
Despite limited resources at the time, researchers had already determined that neuroblastoma was composed of at least 2 distinct cellular populations by the 1980s: neuronal (N-type) cells, characterized by their neuronal phenotype along with their release of neurotransmitters, as well as substrate adhesive (S-type) cells, which produce collagen and fibronectin (both supporting proteins involved in the extracellular matrix) (Zeineldin et al., 2022; To & Midwood, 2011). Researchers later re-termed these populations as ADRN and MES-type cells respectively with subsequent analyses, and further characterized their unique gene expression signatures (van Groningen et al., 2017; Zeineldin et al., 2022).
CURRENT TREATMENTS
Current treatment methods vary depending on the severity of the tumor (Jiang et al., 2011). Low-risk neuroblastoma treatment is typically treated with surgery alone, while high-risk neuroblastoma still does not have a definitive cure as the five-year overall survival rate is still ~60% even with modern therapies (Krystal & Foster, 2023). The treatment regimen for high-risk neuroblastoma is multimodal, involving initial chemotherapy and surgery to remove the visible tumor followed by more chemotherapy and radiation in the consolidation phase to account for any remaining components of the disease (Krystal & Foster, 2023; Bartolucci et al., 2022). To buffer for the high dose of chemotherapy, autologous stem cell transplantation (ASCT) is also conducted in the consolidation phase involving collecting stem cells from the patient for later transplantation after chemotherapy (Krystal & Foster, 2023; Bartolucci et al., 2022). Finally, the subsequent maintenance phase involves anti-GD2 immunotherapy—targeting the GD2 antigen often expressed in neuroblastoma—as well as isotretinoin treatment, which promotes differentiation and halting of proliferation in neuroblastoma (Bartolucci et al., 2022). In particular, researchers have demonstrated that ATRA (all-trans retinoic acid, the metabolite of isotretinoin) treatment of MYCN-amplified neuroblastoma reduced growth and promoted neuronal differentiation (Zimmerman et al., 2021). MES-type neuroblastoma cells, however, are particularly problematic for many of these current treatments; researchers indicate that these cells are more resistant to chemotherapy, RA, anti-GD2 immunotherapy, and various drugs (Zeineldin et al., 2022; van Groningen et al., 2017). This is especially an issue as surviving MES-type cells can interconvert to ADRN-type cells, thus renewing the tumor (Zeineldin et al., 2022). Ultimately, researchers suggest that targeting these problematic MES-type neuroblastoma cells may be a promising avenue for new research in paving the way towards a cure (Zeineldin et al., 2022; van Groningen et al., 2017).
About the Author
Kevin Cho (‘26) is a junior at Harvard College concentrating in neuroscience.
References
- Bahar, M. E., Kim, H. J., & Kim, D. R. (2023). Targeting the RAS/RAF/MAPK Pathway for Cancer Therapy: From Mechanism to Clinical Studies. Signal Transduction and Targeted Therapy, 8(1), 1–38. https://doi.org/10.1038/s41392-023-01705-z
- Bartolucci, D., Montemurro, L., Raieli, S., Lampis, S., Pession, A., Hrelia, P., & Tonelli, R. (2022). MYCN Impact on High-Risk Neuroblastoma: From Diagnosis and Prognosis to Targeted Treatment. Cancers, 14(18), 4421. https://doi.org/10.3390/cancers14184421
- Cesare, A. J., & Reddel, R. R. (2010). Alternative Lengthening of Telomeres: Models, Mechanisms and Implications. Nature Reviews Genetics, 11(5), 319–330. https://doi.org/10.1038/nrg2763
- Huang, M., & Weiss, W. A. (2013). Neuroblastoma and MYCN. Cold Spring Harbor Perspectives in Medicine, 3(10), a014415. https://doi.org/10.1101/cshperspect.a014415
- Jiang, M., Stanke, J., & Lahti, J. M. (2011). The Connections Between Neural Crest Development and Neuroblastoma. Current Topics in Developmental Biology, 94, 77–127. https://doi.org/10.1016/B978-0-12-380916-2.00004-8
- Krystal, J., & Foster, J. H. (2023). Treatment of High-Risk Neuroblastoma. Children, 10(8), 1302. https://doi.org/10.3390/children10081302
- Lahalle, A., Lacroix, M., De Blasio, C., Cissé, M. Y., Linares, L. K., & Le Cam, L. (2021). The p53 Pathway and Metabolism: The Tree That Hides the Forest. Cancers, 13(1), 133. https://doi.org/10.3390/cancers13010133
- Maris, J. M. (2010). Recent Advances in Neuroblastoma. The New England Journal of Medicine, 362(23), 2202–2211. https://doi.org/10.1056/NEJMra0804577
- Otte, J., Dyberg, C., Pepich, A., & Johnsen, J. I. (2021). MYCN Function in Neuroblastoma Development. Frontiers in Oncology, 10. https://doi.org/10.3389/fonc.2020.624079
- Pastorino, F., Capasso, M., Brignole, C., Lasorsa, V. A., Bensa, V., Perri, P., Cantalupo, S., Giglio, S., Provenzi, M., Rabusin, M., Pota, E., Cellini, M., Tondo, A., De Ioris, M. A., Sementa, A. R., Garaventa, A., Ponzoni, M., & Amoroso, L. (2023). Therapeutic Targeting of ALK in Neuroblastoma: Experience of Italian Precision Medicine in Pediatric Oncology. Cancers, 15(3), 560. https://doi.org/10.3390/cancers15030560
- Ponzoni, M., Bachetti, T., Corrias, M. V., Brignole, C., Pastorino, F., Calarco, E., Bensa, V., Giusto, E., Ceccherini, I., & Perri, P. (2022). Recent Advances in the Developmental Origin of Neuroblastoma: An Overview. Journal of Experimental & Clinical Cancer Research, 41(1), 92. https://doi.org/10.1186/s13046-022-02281-w
- Qiu, B., & Matthay, K. K. (2022). Advancing Therapy for Neuroblastoma. Nature Reviews Clinical Oncology, 19(8), 515–533. https://doi.org/10.1038/s41571-022-00643-z
- To, W. S., & Midwood, K. S. (2011). Plasma and Cellular Fibronectin: Distinct and Independent Functions During Tissue Repair. Fibrogenesis & Tissue Repair, 4(1), 21. https://doi.org/10.1186/1755-1536-4-21
- Tsubota, S., & Kadomatsu, K. (2017). Origin and Mechanism of Neuroblastoma. Oncoscience, 4(7–8), 70–72. https://doi.org/10.18632/oncoscience.360
- Van Arendonk, K. J., & Chung, D. H. (2019). Neuroblastoma: Tumor Biology and Its Implications for Staging and Treatment. Children, 6(1), Article 1. https://doi.org/10.3390/children6010012
- van Groningen, T., Koster, J., Valentijn, L. J., Zwijnenburg, D. A., Akogul, N., Hasselt, N. E., Broekmans, M., Haneveld, F., Nowakowska, N. E., Bras, J., van Noesel, C. J. M., Jongejan, A., van Kampen, A. H., Koster, L., Baas, F., van Dijk-Kerkhoven, L., Huizer-Smit, M., Lecca, M. C., Chan, A., … Versteeg, R. (2017). Neuroblastoma Is Composed of Two Super-Enhancer-Associated Differentiation States. Nature Genetics, 49(8), 1261–1266. https://doi.org/10.1038/ng.3899
- Zeineldin, M., Patel, A. G., & Dyer, M. A. (2022). Neuroblastoma: When Differentiation Goes Awry. Neuron, 110(18), 2916–2928. https://doi.org/10.1016/j.neuron.2022.07.012
- Zimmerman, M. W., Durbin, A. D., He, S., Oppel, F., Shi, H., Tao, T., Li, Z., Berezovskaya, A., Liu, Y., Zhang, J., Young, R. A., Abraham, B. J., & Look, A. T. (n.d.). Retinoic Acid Rewires the Adrenergic Core Regulatory Circuitry of Childhood Neuroblastoma. Science Advances, 7(43), eabe0834. https://doi.org/10.1126/sciadv.abe0834