A single institution experience of multimodality radiation therapy for muscle-invasive bladder cancer

e16614 Background: We studied a cohort of patients with localized muscle invasive bladder cancer (MIBC) who received organ preserving trimodality therapy (TMT) as definitive treatment at a single high-volume institution. Methods: A retrospective cohort analysis was performed for 231 bladder cancer patients treated with definitive radiation or chemoradiation therapy from 2006 to 2022 at a single institution. We assessed overall and disease-free survival as defined by any type of cancer recurrence. We analyzed survival outcomes based on stage, pathologic features, and patient characteristics. Results: 184 of 231 patients in this cohort received either definitive radiation therapy alone or with chemoradiation and had adequate follow-up data for analysis. The median overall survival for these 184 patients was 37mo (95%CI 28-67). Disease free survival (DFS) had a median time of 36mo (95% CI 23-69). On univariate analysis neither tumor size nor hydronephrosis showed a significant association with local recurrence. The presence of carcinoma in situ (CIS) was associated with shorter time to local recurrence (Log-Rank p = 0.039). Nine patients (4.9%) required cystectomy after initial definitive radiation therapy. When overall survival was compared between patients offered radical cystectomy who proceeded with definitive multimodal radiation therapy and radical cystectomy ineligible patients, there was a significantly longer overall survival for the cystectomy eligible patients (median 86mo (95%CI 35-206) vs median 31mo (95%CI 24-44), Log-Rank p = 0.0016). No differences were observed in cancer specific survival between cystectomy eligible and ineligible patients. Conclusions: Multimodality bladder preservation demonstrated cancer specific survival outcomes comparable to published radical cystectomy series. The presence of CIS at baseline was associated with increased local recurrence, but not CSS or OS. Eligibility for radical cystectomy was associated with longer overall survival in patients treated with TMT, highlighting the limitations of retrospective comparisons of all-cause mortality between different treatment approaches. Disease specific survival endpoints, propensity matching analyses, or randomized prospective trials are needed to draw comparative efficacy conclusions.