International Society of Urological Pathology Multidisciplinary Expert Consultation Conference on Evaluation of Treatment Effects in Prostate and Bladder Cancer: Working Group 2: The Urinary Bladder.

Treatment effects in the urinary bladder are variable and range from localized post-transurethral resection changes to widespread systemic therapy effects. The International Society of Urological Pathology (ISUP) organized a consensus meeting in Vienna, Austria, in September 2025, focused on the evaluation of treatment effects in both the prostate and bladder. Working Group 2 was assigned the topic of the urinary bladder, and a group of pathologists and clinicians was convened. They worked cooperatively to develop a 30-question, premeeting survey for the ISUP membership, which covered the following topics: systemic therapy-related changes, intravesical therapy and radiotherapy-related changes, macroscopic examination and reporting of treated bladder specimens, and relevant ancillary testing methods for grossly residual and/or minimal residual disease. The premeeting survey results highlighted uncertainty about tumor regression grading (TRG), variability in reporting practices for post-resection and intravesical therapy cases, and divergent opinions on the potential utility of molecular testing. Based on findings from this crowd-sourced experience, the Working Group researched the primary medical literature to study the problematic premeeting survey topics, curated focused presentations of published experience for the consensus meeting participants and developed refined consensus questions for consensus voting. Consensus was achieved in 18/19 polling statements. Use of molecular tests to distinguish benign mimickers from carcinoma did not reach consensus. Overall, the surveys and in-person consensus voting supported standardized reporting practices and terminology for post-therapy cases, interdisciplinary development of a bladder TRG scheme, and the utility of select molecular and immunohistochemical testing in the post-treatment setting.