Efficacy of avelumab maintenance therapy for advanced urothelial carcinoma with histologic subtype and divergent differentiation: a multicenter retrospective study conducted by the Uro-Oncology Group in Kyushu

Background: The subtype of urothelial carcinoma (SUC) has been known to possess morphological diversity for histologic subtype or divergent differentiation. However, the efficacy of avelumab against SUC remains unclear. Therefore, the effect of the treatment as well as the survival results of avelumab monotherapy were evaluated as a first-line therapeutic maintenance in patients with advanced SUC. Methods: A retrospective analysis was conducted on consecutive patients from the Uro-Oncology Group in Kyushu study population with advanced lower and upper urinary tract cancer who underwent avelumab maintenance therapy without progression after first-line platinum-based chemotherapy. Patients with pure urothelial carcinoma (PUC) and SUC were comparatively analyzed based on objective response rate (ORR), disease control rate, progression-free survival (PFS), and overall survival (OS). Results: Out of 49 recorded patients, 38 and 11 had PUC and SUC, respectively. The most common subtype element was glandular differentiation (n=5), followed by squamous differentiation (n=3), micropapillary (n=1), and plasmacytoid subtypes (n=1). The SUC and PUC groups had comparable ORR (0% vs. 2.6%, P>0.99) and disease control rates (54.5% vs. 44.7%, P=0.73). These patient groups also showed no significant difference in PFS (median 3.9 vs. 3.1 months, P=0.33) or OS (median 16.7 vs. 22.1 months, P=0.47). Conclusions: The response of SUC and PUC to avelumab was comparable in patients with advanced lower and upper urinary tract cancer, indicating that avelumab maintenance therapy is also effective for SUC