Comparison of the survival outcomes between primary and secondary muscle-invasive bladder cancer: a propensity score-matched study

Background:Studies have classified muscle-invasive bladder cancer (MIBC) into primary (initially muscle-invasive, PMIBC) and secondary subtypes (initially non-muscle-invasive but progresses, SMIBC), for which controversial survival outcomes were demonstrated. This study aimed to compare the survival outcomes between PMIBC and SMIBC patients in China.Methods:Patients diagnosed with PMIBC or SMIBC at West China Hospital from January 2009 to June 2019 were retrospectively included. Kruskal-Wallis and Fisher tests were employed to compare clinicopathological characteristics. Kaplan-Meier curves and Cox competing proportional risk model were used to compare survival outcomes. Propensity score matching (PSM) was employed to reduce the bias and subgroup analysis was used to confirm the outcomes.Results:A total of 405 MIBC patients were enrolled, including 286 PMIBC and 119 SMIBC, with a mean follow-up of 27.54 and 53.30 months, respectively. The SMIBC group had a higher proportion of older patients (17.65% [21/119] vs. 9.09% [26/286]), chronic disease (32.77% [39/119] vs. 22.38% [64/286]), and neoadjuvant chemotherapy (19.33% [23/119] vs. 8.04% [23/286]). Before matching, SMIBC had a lower risk of overall mortality (OM) (hazard ratios [HR] 0.60, 95% confidence interval [CI] 0.41-0.85, P = 0.005) and cancer-specific mortality (CSM) (HR 0.64, 95% CI 0.44-0.94, P = 0.022) after the initial diagnosis. However, higher risks of OM (HR 1.47, 95% CI 1.02-2.10, P = 0.038) and CSM (HR 1.58, 95% CI 1.09-2.29, P = 0.016) were observed for SMIBC once it became muscle-invasive. After PSM, the baseline characteristics of 146 patients (73 for each group) were well matched, and SMIBC was confirmed to have an increased CSM risk (HR 1.83, 95% CI 1.09-3.06, P = 0.021) than PMIBC after muscle invasion.Conclusions:Compared with PMIBC, SMIBC had worse survival outcomes once it became muscle-invasive. Specific attention should be paid to non-muscle-invasive bladder cancer with a high progression risk.