B7-H3: a consistent marker in metastatic colorectal cancer with potential for targeted treatment.

Colorectal cancer (CRC) remains a leading cause of cancer-related morbidity and mortality worldwide. Despite advances in various treatment approaches, outcomes for patients with metastatic CRC (mCRC) remain poor, and treatment-associated side effects significantly impact quality of life. While immunotherapy has shown promise in certain malignancies, its efficacy in CRC is limited to a minority of patients, highlighting the urgent need for novel therapeutic targets to improve treatment efficacy while minimizing off-target effects. B7-H3 (CD276) has emerged as a promising immunotherapeutic target due to its selective expression on tumor cells and neovasculature, with minimal presence in healthy tissues. A novel IgG-based bispecific antibody targeting B7-H3 and CD3, CC-3, has demonstrated strong preclinical efficacy in stimulating T cell-mediated antitumor responses and is currently being evaluated in a first-in-human trial including patients with mCRC (NCT05999396). In this study, we investigated B7-H3 expression in a cohort of n = 55 mCRC patients and assessed its correlation with demographic, pathological, and molecular factors, as well as clinical outcomes. Additionally, to evaluate the stability of B7-H3 expression over time, we analyzed sequential biopsies from metastatic lesions from n = 7 patients at subsequent time points. Our findings demonstrate that B7-H3 is consistently overexpressed in mCRC, independent of demographic factors, primary tumor localization (right vs. left colon), common molecular and genetic alterations (HER2, MSI, KRAS, NRAS, BRAF, PIK3CA, p53), and serum tumor markers. Longitudinal analysis showed that B7-H3 expression was comparable or increased over time in sequential metastatic specimens. No significant association was observed between B7-H3 expression and overall survival or progression-free survival, and prior chemotherapy treatment did not influence B7-H3 expression levels. In conclusion, B7-H3 is stably and ubiquitously expressed in mCRC, reinforcing its potential as a robust target for immunotherapeutic strategies, including bispecific antibodies. The lack of variability across patient subgroups suggests that routine pre-treatment assessment of B7-H3 may not be necessary. These findings provide a strong rationale for the continued clinical evaluation of B7-H3-targeted therapies, such as CC-3 (NCT05999396), in mCRC patients.