PURPOSE

B7 homolog 3 (B7-H3) is a promising target for antibody-drug conjugates, with ifinatamab deruxtecan demonstrating an objective response rate of 54.8% in previously treated extensive-stage small cell lung cancer (SCLC). This analysis aimed to characterize B7-H3 RNA expression with reference to SCLC molecular subtypes (SCLC-A, SCLC-N, SCLC-P, and SCLC-I) and immune-related parameters.

EXPERIMENTAL DESIGN

Tumor RNA expression and mutational burden for 1,721 patients with SCLC were derived from a real-world database (Caris Life Sciences). A predominant molecular subtype was assigned based on RNA expression using a gene-ratio classifier. PD-L1 expression was assessed by IHC (antibody 22C3; positive cutoff: tumor proportion score ≥1%).

RESULTS

The predominant molecular subtype was SCLC-A in 848 (49.3%), SCLC-N in 202 (11.7%), SCLC-P in 142 (8.3%), SCLC-I in 291 (16.9%), and equivocal in 238 (13.8%) samples. B7-H3 expression was high and consistent among subtypes (q > 0.05), whereas DLL3 and SEZ6 expression each differed significantly (both q < 0.0001). PD-L1 positivity was similar across B7-H3 expression quartiles (range, 39.2%-46.5%). Median (95% confidence interval) B7-H3 expression was comparable between patients with and without prior immunotherapy [18.7 (16.5-21.2) and 17.3 (16.4-18.1) transcripts per million, respectively]. B7-H3 was not correlated with a T-cell signature but showed a strong correlation with HAVCR2/TIM3, CD86, PDCD1LG2/PD-L2, and M2 macrophages.

CONCLUSIONS

B7-H3 showed consistent, high expression across SCLC molecular subtypes, whereas DLL3 and SEZ6 expression varied significantly. These data suggest that B7-H3-targeting antibody-drug conjugates may be active across SCLC subtypes, consistent with the high reported response rates.