Tumor volumes as a predictor of response to the anti-EGFR antibody drug conjugate depatuxizumab mafadotin.

Background The adverse impact of increasing brain tumor size on the efficacy of antibody-drug conjugates (ADCs) was investigated preclinically then validated with clinical data. Methods—Preclinical study The impact of tumor size on ADC tumor delivery and treatment response was evaluated in an EGFR-amplified patient-derived glioblastoma (GBM) model following treatment with Depatuxizumab mafadotin (Depatux-M). Biodistribution and imaging studies correlated drug distribution with starting treatment volume and anti-tumor activity. Methods—Clinical study M12-356 was a Phase I study of Depatux-M in patients with GBM. Blinded volumetric analysis of baseline tumor volumes of M12-356 patients was undertaken by two reviewers and results correlated with response and survival. Results Preclinically, imaging and biodistribution studies showed specific and significantly higher tumor uptake of zirconium-89 labeled Depatux-M (89Zr-Depatux-M) in mice with smaller tumor volume (~98 mm3) versus those with larger volumes (~365 mm3); concordantly, mice with tumor volumes ≤100 mm3 at treatment commencement had significantly better growth inhibition by Depatux-M (93% vs 27%, P < .001) and significantly longer overall survival (P < .0001) compared to tumors ≥400 mm3. Clinically, patients with tumor volumes <25 cm3 had significantly higher response rates (17% vs. 0%, P = .009) and longer overall survival (0.5 vs 0.89 years, P = .001) than tumors above 25 cm3. Conclusion Both preclinical and clinical data showed intra-tumoral concentration and efficacy of Depatux-m inversely correlated with tumor size. This finding merit further investigation with pretreatment tumor volume as a predictor for response to ADCs, in both gliomas and other solid tumors.