Neoadjuvant Pembrolizumab and Accelerated Methotrexate, Vinblastine, Doxorubicin, and Cisplatin in Nonurothelial Histologic Subtypes of Muscle-invasive Bladder Cancer: A Phase 2 Trial.

Muscle-invasive bladder cancer (MIBC) with histologic subtypes represents a clinical challenge because of poor responses to conventional therapies and under-representation in clinical trials. This single-center phase 2 trial evaluated the combination of neoadjuvant pembrolizumab and accelerated methotrexate, vinblastine, doxorubicin, and cisplatin (aMVAC) chemotherapy in patients with pure or predominant nonurothelial histologies. Seventeen patients were enrolled, with squamous differentiation being the most common variant. The primary endpoint, a pathologic complete response (pCR), was achieved in nine of 17 patients (53%), with an additional patient achieving ypTisN0 (downstaging rate 59%) and another achieving a clinical complete response. Grade ≥3 toxicities were observed in 47% of patients, primarily attributable to aMVAC. At median follow-up of 35 mo (range 11-48) the estimated 2-yr event-free survival (EFS) and overall survival rates were 64% (95% confidence interval 32-84%) and 79% (95% confidence interval 47-93%), respectively. Preliminary biomarker analysis did not reveal significant correlations between immune-cell subsets at baseline and pCR or EFS. These findings suggest that chemoimmunotherapy is a very promising approach for MIBC with histology subtypes. Larger studies are warranted to further refine therapeutic strategies.