Genetic and Histopathological Heterogeneity of Neuroblastoma and Precision Therapeutic Approaches for Extremely Unfavorable Histology Subgroups

Abstract

Peripheral neuroblastic tumors (neuroblastoma, ganglioneuroblastoma and ganglioneuroma) are heterogeneous and their diverse and wide range of clinical behaviors (spontaneous regression, tumor maturation and aggressive progression) are closely associated with genetic/molecular properties of the individual tumors. The International Neuroblastoma Pathology Classification, a biologically relevant and prognostically significant morphology classification distinguishing the favorable histology (FH) and unfavorable histology (UH) groups in this disease, predicts survival probabilities of the patients with the highest hazard ratio. The recent advance of neuroblastoma research with precision medicine approaches demonstrates that tumors in the UH group are also heterogeneous and four distinct subgroups-MYC, TERT, ALT and null-are identified. Among them, the first three subgroups are collectively named extremely unfavorable histology (EUH) tumors because of their highly aggressive clinical behavior. As indicated by their names, these EUH tumors are individually defined by their potential targets detected molecularly and immunohistochemically, such as MYC-family protein overexpression, TERT overexpression and ATRX (or DAXX) loss. In the latter half on this paper, the current status of therapeutic targeting of these EUH tumors is discussed for the future development of effective treatments of the patients.

Keywords: ALT; International Neuroblastoma Pathology Classification; MYC; TERT; extremely unfavorable histology; neuroblastoma.

Figure 1

Neuroblastoma, prognostic factors and hazard ratios. * Clinical stage according to the International Neuroblastoma Risk Group Staging System; ** SCA = segmental chromosomal aberrations; *** INPC = International Neuroblastoma Pathology Classification (FH = favorable histology, UH = unfavorable histology). Note: Clinical stage (localized (L1 and L1) and MS (metastatic, special) disease vs. M (metastatic) disease) and INPC (FH group vs. UH group) distinguish tow prognostic groups with very high hazard ratio.

Figure 2

Children’s Oncology Group revised neuroblastoma risk classification system. For detailed explanation of the revised classification system, please see Ref. [8]. (Irwin M. et al., 2021 [8]).

Figure 3

Histologic features of peripheral neuroblastic tumors: (A) neuroblastoma (Schwannian stroma-poor), undifferentiated subtype (original, ×200); (B) neuroblastoma (Schwannian stroma-poor), poorly differentiated subtype (original, ×200); (C) neuroblastoma (Schwannian stroma-poor), differentiating subtype (original, ×200); (D) ganglioneuroblastoma, intermixed (Schwannian stroma-rich) (original, ×100); (E) ganglioneuroma (Schwannian stroma-dominant)—note that completely mature ganglion cells are covered with satellite cells (arrows) (original, ×200); (F) ganglioneuroblastoma, nodular (composite, Schwannian stroma-rich/stroma-dominant and stroma-poor)—note two distinct histologies, i.e., neuroblastoma in the upper half and ganglioneuroma in the lower half in this case (original ×100); (G) Ki-67 immunostaining on two neuroblastomas of poorly differentiated subtype with a low mitosis–karyorrhexis index (original ×400). Note: (G-1) shows biopsy from rapidly enlarging liver of 3-month-old baby (Stage MS case, favorable histology) before starting spontaneous regression; (G-2) shows biopsy from abdominal mass of 5-year-old child (Stage M case, unfavorable histology). The favorable histology tumor contains numerous and more Ki-67 positive nuclei than the unfavorable histology tumor. (H) MYCN oncogene-amplified neuroblastoma demonstrating a characteristic histology of poorly differentiated subtype with a high mitosis–karyorrhexis index (original, ×400). Note: Tumor cells show nucleolar hypertrophy (Inset: prominent nucleoli indicated by arrows).

Figure 4

International Neuroblastoma Pathology Classification: patient distribution by age at diagnosis. Note: Most of the patients having favorable histology tumors are clinically detected and diagnosed in younger-age groups than the patients having unfavorable histology tumors.

Figure 5

Proposed subgroupings of unfavorable histology neuroblastomas. Four subgroups, i.e., MYC (overexpressing either MYCN or MYC protein), TERT (TERT gene activation due to rearrangements), ALT (due to ATRX or DAXX loss) and null (no MYC, No TERT, no ALT), are distinguished immunohistochemically. EUH, extremely unfavorable histology; UH, unfavorable histology. The immunohistochemical grading of MYC-family protein expression was performed according to Ref. [25] using monoclonal anti-MYCN, NCM II 100 and anti-MYC, Y69. The evaluation of ATRX loss was performed when tumor cell nuclei were negative and endothelial cell nuclei (built-in-control) were positive in the same tumor tissue using polyclonal HPA001906. The immunohistochemical grading of TERT was performed essentially the same way as MYC-family proteins [25] using monoclonal A-6. (Adopted from the article by Ikegaki and Shimada, JCO Precis Oncol 2019;3:PO18.00312 [24] with the publisher’s permission.). (All images, original ×600).