Selective bladder-sparing trial with sasanlimab as maintenance treatment based on clinical response to neoadjuvant treatment in molecularly categorized muscle invasive bladder cancer patients: SASAN-SPARING trial.

TPS4644 Background: Muscle-invasive bladder cancer (MIBC) is an aggressive disease with a high risk of progression, for which radical cystectomy (RC) remains the standard of care. Adaptive bladder-sparing strategies based on post-neoadjuvant clinical restaging are increasingly explored to maintain oncologic control while preserving quality of life. SASAN-SPARING evaluates sasanlimab, a PD-1 inhibitor, as maintenance therapy in patients achieving a clinical response after neoadjuvant cisplatin-based chemotherapy. Methods: SASAN-SPARING (HM-8788561; NCT06623162) is an ongoing, single-arm, multicenter, phase II trial enrolling patients aged ≥18 years with treatment-naïve, localized MIBC (pT2–T4a, N0, M0) eligible for neoadjuvant chemotherapy. All patients receive four cycles of cisplatin (70 mg/m² on day 1) plus gemcitabine (1000 mg/m² on days 1 and 8) every 3 weeks, followed by comprehensive clinical restaging. Patients achieving a clinical response (cT0/Ta/T1/Tis, negative cytology, and negative imaging) are eligible for bladder preservation with sasanlimab 300 mg administered subcutaneously every 4 weeks for up to 12 cycles. Non-responders (≥cT2) undergo RC. During maintenance, restaging is performed every 12 weeks, and RC may be considered upon loss of response or disease progression. The primary endpoint is bladder-intact overall survival at 12 months after the first dose of sasanlimab. Secondary endpoints include disease-free survival, metastasis-free survival, overall survival, safety, and health-related quality of life. The study incorporates an ambitious biomarker analysis, including whole-genome sequencing of tumour tissue and plasma, the use of ctDNA in plasma and urine for tumour assessment and molecular dynamics, and the study of the gut microbiome in stool. Biomarker-correlative studies will provide a valuable tool for personalized treatments and inform treatment decisions in adaptive strategies such as SASAN-SPARING. The Expected sample size is 70 patients, assuming a 12-month biOS of 81% (H0) and an increase with sasanlimab up to 93% (H1) (one-arm survival test; α=0.05 β=0.8).Recruitment began in December 2024. As of January 2026, 62 patients have been enrolled across 10 centers, and 21 started sasanlimab maintenance therapy. Enrollment is ongoing.SASAN-SPARING explores an adaptive, biomarker-integrated bladder-sparing strategy which aims to generate prospective evidence to support organ-preservation strategies in MIBC. Clinical trial information: NCT06623162 .