High B7-H3 protein expression in Medulloblastoma is associated with metastasis and unfavorable patient outcomes

Abstract

Background: Medulloblastoma (MB) is the most common malignant brain tumor in children. Although the 5-year survival rate is approximately 70-80%, the current standard treatment results in severe and long-term side effects. The search for new anticancer immunotherapeutic targets has identified B7-H3 as a promising candidate in various solid tumors. However, the role of B7-H3 in MB remains unclear, and studies reporting its protein expression and association with clinicopathological characteristics are still limited.

Methods: In this study, B7-H3 protein expression was evaluated by immunohistochemistry in seven non-tumor samples and 43 molecularly characterized MB tissues. Its expression profile was correlated with B7-H3 (CD276) mRNA levels, which were previously determined by nCounter, as well as with the patients' clinical features.

Results: Only 14.3% (1/7) of non-tumor brain and cerebellum tissues showed B7-H3 positivity, whereas 95.6% (41/43) of the MB samples expressed this protein at distinct levels. B7-H3 was found in the cytoplasm and on the membrane of cancer cells. A significant positive correlation was observed between CD276 mRNA and B7-H3 protein levels. Moreover, high expression of B7-H3 protein was associated with worse overall survival and the presence of metastasis at diagnosis.

Conclusions: This is the first study to associate CD276 mRNA and B7-H3 protein levels in MB, revealing a significant positive correlation. We observed that B7-H3 was overexpressed in MB compared to non-tumor brain tissue. High B7-H3 expression was associated with a worse outcome and with the presence of metastasis at diagnosis.

Keywords: B7-H3; CD276; Immunotherapy; Medulloblastoma; Metastasis; Prognostic marker.

Fig. 1

Immunohistochemistry analysis of B7-H3 in MB and non-tumor samples. (A and B) Non-tumor cerebellum with negative B7-H3 expression (100X and 200X magnification, respectively). (C) Membranous expression on a brain metastasis from a breast metastatic adenocarcinoma (400X magnification). (D) MB weak cytoplasmic expression (400X magnification). (E) and (F) MB strong cytoplasmic and membranous expression (400X magnification)

Fig. 2

B7-H3 score across the molecular subgroups of MB. Group comparisons were performed using Kruskal-Wallis test (H = 19.62, df = 5, p = 0.0006). For pairwise post hoc comparisons, Dunn’s test was applied, and a significant increase of B7-H3 scores was observed in WNT, SHH and Group 4 MB compared to non-tumor tissue (p = 0.0161, p = 0.0004 and p = 0.0147, respectively). P-values are graphically represented as follows: p > 0.05, ns; *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001; and ****p ≤ 0.0001

Fig. 3

Overall survival according to B7-H3 expression in MB. (A) MB patients (n = 41) were categorized into two groups according to B7-H3 expression levels: low/moderate and high. OS probabilities were estimated using the Kaplan-Meier method, and survival distributions were compared via the log-rank test (χ² = 6.791, df = 1, p = 0.009). High B7-H3 expression was significantly associated with shorter OS. The median survival time for patients with high B7-H3 expression was 83.7 months (95% CI: 3.9-163.5), whereas the median survival time for patients with low/moderate B7-H3 expression was not reached during the follow-up period. (B) Patients were further stratified based on B7-H3 cellular localization (cytoplasm only vs. cytoplasmic/membranous expression). In the two subgroups, high B7-H3 expression was associated with lower survival probabilities. However, a significant association with a worse OS was observed only in patients with cytoplasmic/membranous B7-H3 expression (log-rank test: χ² = 4.046, df = 1, p = 0.044)