Objective: To compare the therapeutic effect of Bacille Calmette-Guérin (BCG) intravesical instillation in older and younger patients with high-risk non-muscle-invasive bladder cancer. The comparison was performed with propensity score matching (PSM) without terminating the death of the older patients using relatively large-scale retrospective data from multiple institutes in Japan. Materials and Methods: Overall, 3283 patients diagnosed with non-muscle-invasive bladder cancer treated with intravesical BCG instillation during 2000-2018 in 31 institutes were examined; 1437 and 602 patients with high-grade T1 and Tis tumors were divided into those aged ≥75 and <75 years. Multivariate analysis using the Fine–Gray competing risks regression model before PSM and survival analysis using the cumulative incidence method after PSM were performed. Results: In the pre-PSM series of high-grade T1 tumors, age ≥75 years was an independent prognostic factor for both recurrence and progression in multivariate analysis (P = .015 and P = .013). In the pre-PSM series with Tis tumor, no variables to predict recurrence and progression was found. In the post-PSM series of 870 high-grade T1 tumors, cumulative probability of recurrence after BCG intravesical instillation were significantly higher in patients aged ≥75 years than in those aged <75 years (P = .008). The frequency of discontinuation of BCG instillation in patients aged ≥75 years with high-grade T1 and Tis was not significantly different from those in patients aged <75 years (P = .564 and P = .869). Conclusion: The cumulative probability of recurrence after intravesical BCG instillation was significantly higher in older than in younger patients with high-grade T1 bladder cancer.
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