Diversity in B7-H3/CD276 expression across cancer types: Exploring a dynamic novel immune checkpoint.

3133 Background: The resistance encountered in immune checkpoint blockade has persistently impaired the achievement of robust, durable antitumor immune responses in most cancer patients, prompting the search for additional immune targets. B7 homolog 3 (B7-H3)/CD276 is an emerging immune biomarker whose contrasting immune functions challenge conventional immune marker classifications, making it a compelling target. The present study aimed to characterize the expression of B7-H3/CD276 in a pan-cancer setting, analyze its co-expression patterns with potentially co-targetable immune checkpoints, and discuss implications for ongoing clinical trials. Methods: We conducted a focused analysis of B7-H3/CD276 expression in 514 cancer patients with diverse tumor histologies evaluated under the PREDICT protocol at the University of California San Diego. RNA sequencing of tissue specimens was performed, and results were used to characterize the RNA expression levels of B7-H3/CD276 and its correlation with key cancer immunity markers including PD-1, PD-L1, PD-L2, CTLA4, LAG3, BTLA, TIM3, VISTA, ADORA2A and IDO1. Results: Elevated expression levels of B7-H3/CD276 were observed in 41.6% 214/514 of the 514 tumor samples analyzed. When stratified by cancer type, the highest rates of elevated expression were found in sarcomas (58.30%, 14/24), followed by pancreatic (58.20%, 32/55) and liver and bile duct cancers (52.60%, 10/19). The independent association with pancreatic cancers was statistically significant on multivariate analysis (odds ratio 2.20, 95% confidence interval 1.09 – 4.45, p = 0.027). Ninety-three unique patterns of immune co-expression were observed among the 214 patients with high B7-H3/CD276 expression levels. Among them, the most commonly observed pattern was high expression of B7-H3/CD276 alone (26.2%, 56/214) followed by co-expression with high VISTA (7.0%, 15/214) and high ADORA2A (5.6%, 12/214). Of note, there was significant heterogeneity observed in the patterns of co-expression in cancer immunity markers, with 72.04% (67/93) in the cohort being unique to one patient. Conclusions: We have observed immunomic diversity in our analysis of B7-H3/CD276 expression levels across varied tumor types as well as in its co-expression patterns with other immune markers. Our findings suggest that leveraging immune profiling to build customized therapeutic regimens may be pertinent to optimizing response rates and minimizing toxicity to B7-H3/CD276 targeting therapies.