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.