Prognosis of patients with T1 low-grade urothelial bladder cancer treated with bacillus Calmette-Guérin immunotherapy.

BACKGROUND: The existence and prognosis of T1LG (T1 low-grade) bladder cancer is controversial. Also, because of data paucity, it remains unclear what is the clinical history of bacillus Calmette-Guérin (BCG) treated T1LG tumors and if it differs from other NMIBC (non-muscle-invasive bladder cancer) representatives. The aim of this study was to analyse recurrence-free survival (RFS) and progression-free survival (PFS) in patients with T1LG bladder cancers treated with BCG immunotherapy. METHODS: A multi-institutional and retrospective study of 2510 patients with Ta/T1 NMIBC with or without carcinoma in situ (CIS) treated with BCG (205 T1LG patients) was performed. Kaplan-Meier estimates and log-rank test for RFS and PFS to compare the survival between TaLG, TaHG, T1LG, and T1HG NMIBC were used. Also, T1LG tumors were categorized into EAU2021 risk groups and PFS analysis was performed, and Cox multivariate model for both RFS and PFS were constructed. RESULTS: The median follow-up was 52 months. For the T1LG cohort, the estimated RFS and PFS rates at 5-year were 59.3% and 89.2%, respectively. While there were no differences in RFS between NMIBC subpopulations, a slightly better PFS was found in T1LG NMIBC compared to T1HG (5-year PFS; T1LG vs. T1HG: 82% vs. 89%; P<0.001). A heterogeneous classification of patients with T1LG NMIBC was observed when EAU 2021 prognostic model was applied, finding a statistically significant worse PFS in patients classified as high-risk T1LG (5-year PFS; 81.8%) compared to those in intermediate (5-year PFS; 93,4%), and low-risk T1LG tumors (5-year PFS; 98,1%). CONCLUSIONS: The RFS of T1LG was comparable to other NMIBC subpopulations. The PFS of T1LG tumors was significantly better than of T1HG NMIBC. The EAU2021 scoring model heterogeneously categorized the risk of progression in T1LG tumors and the high-risk T1LG had the worst PFS.