Costello, Brian A

Abstract Enfortumab vedotin (EV), pembrolizumab, and EV plus pembrolizumab (EV/P) have rapidly reshaped the treatment landscape of advanced urothelial carcinoma, but toxicity increasingly determines treatment delivery, treatment continuity, and real-world benefit. As EV/P moves into broader clinical use, clinicians must distinguish adverse events related to antibody-drug conjugate exposure from immune-mediated toxicities and recognize syndromes in which both mechanisms may contribute. In this practical, mechanism-informed review, we synthesize pivotal trials, mature follow-up reports, and representative real-world cohorts describing the safety of EV monotherapy, pembrolizumab monotherapy, and EV/P in urothelial carcinoma. Because adverse-event reporting and ascertainment are heterogeneous across studies, including differences in preferred terms, composite categories, grading frameworks, and treatment-related versus all-cause reporting, we emphasize clinically interpretable patterns rather than pooled estimates. EV monotherapy is characterized by cutaneous toxicity, peripheral neuropathy, hyperglycemia, dysgeusia, and ocular events, including early epithelial/metabolic events and cumulative neuropathy. Pembrolizumab monotherapy has a lower overall high-grade toxicity burden but is defined by immune-mediated endocrinopathies, pneumonitis, hepatitis, colitis, and nephritis. Combination therapy produces a predictable overlap of these toxicity domains, creating diagnostic and management challenges for syndromes such as skin toxicity, diarrhea, fatigue, and pulmonary symptoms. We provide comparative visual toxicity signatures, regimen-specific summary tables, temporal toxicity mapping, and a pragmatic attribution framework that classifies events as EV-predominant, immune-predominant, overlap/indeterminate, or high-risk requiring initial interruption of both agents. This review aims to support bedside recognition, provisional attribution, early management, and safer implementation of EV/P in contemporary urothelial carcinoma practice.