Bladder preservation in muscle invasive bladder cancer (MIBC): A population based analysis.

e16608 Background: Although available data supports trimodal therapy (TMT) as a bladder sparing treatment for MIBC with outcomes comparable to cystectomy, uptake in Canada is low. A retrospective evaluation in British Columbia, Canada, was undertaken to evaluate real-world outcomes in MIBC patients (pts) undergoing bladder sparing radiotherapy (RT). Methods: MIBC pts were identified from the BC Cancer registry who received RT with curative intent between Jan 1, 2002, and Dec 31, 2020. Disease free survival (DFS), overall survival (OS), and disease specific survival (DSS) were calculated for those receiving RT versus combined modality treatments. Further analysis was undertaken to identify factors associated with outcomes. Results: The population was 231 pts, predominantly male (74%), median age 81 (range: 44-95). Almost all (97%) presented with high-grade MIBC, and 67.1% had an ECOG score of 0-1. The reasons for bladder preservation were frailty/comorbidities (77.1%), pt preference (16%) and inoperability (6.9%). 170 (73.6%) pts underwent RT alone; the remainder were treated with chemoRT (16.5%), neoadjuvant chemotherapy (nCT)+RT alone (5.6%), nCT+chemoRT (3%), chemoRT+adjuvantCT (0.9%), and RT+adjuvantCT (0.4%). The median OS in the RT-only group (25.2 months, 95% CI, 19.5-31) was significantly lower than for chemoRT (39.7 months, 95% CI, 13.5-65.9, p=0.013). Pts who underwent maximal transurethral resection of the bladder tumor (TURBT) in the chemoRT group exhibited significantly prolonged OS (56.5 vs. 31.9 months, p=0.006). Pts with maximal TURBT who had a second TURBT while waiting for RT demonstrated a significant improvement, compared to those with a second TURBT due to submaximal TURBT (59.3 vs. 13.3 months, p<.001). Despite these findings, DSS analysis did not show statistically significant differences between the treatment groups (p=0.38), even when stratified by maximal TURBT (p=0.207). Similarly, the median DFS did not represent a difference between the groups (26.6 vs. 22.2 months, p=0.772). Cox regression analysis revealed the absence of carcinoma in situ trended towards a decreased risk of death (HR: 0.52, p<0.001), as did the absence of hydronephrosis (HR: 0.65, p=0.009) and an increase in the total number of RT fractions (HR: 0.92, p=0.001). In the analysis of treatment modalities (RT vs. chemoRT), there was a significant difference in the distribution of recurrence sites (Chi-Square=4.15, p=0.04). Local recurrences were identified less frequently in the chemoRT group. Conclusions: This population-based study showed notable demographic and treatment-related characteristics that influenced OS, DSS, and DFS. While respecting the limitations of retrospective cohort studies, overall outcomes in this cohort are inferior to those predicted for TMT, but adherence to best practices such as maximal TURBT and combined modality chemoRT result in acceptable long term survival rates.