Clinical impact of a subtype of urothelial carcinoma in nonmuscle-invasive bladder cancer

Objective: This study aimed to assess the oncological outcomes of the subtype of urothelial carcinoma (SUC), including divergent differentiation and histologic subtype, in comparison with those of pure urothelial carcinoma (PUC) in nonmuscle-invasive bladder cancer.

Methods: We retrospectively evaluated patients who were initially treated with transurethral resection of the bladder tumor (TURBT) between March 2005 and August 2020 at a single institution. Patients with PUC and SUC were compared in terms of recurrence-free survival (RFS), progression-free survival (PFS), and overall survival (OS).

Results: Out of 853 enrolled patients, 783 (91.8%) and 70 (8.2%) had PUC and SUC, respectively. SUC presence was significantly associated with old age, tumor size (≥3 cm), higher pT1 rate, high grade, concomitant carcinoma in situ, and lymphovascular invasion. RFS rates after TURBT did not significantly differ between the PUC and SUC groups. With a median follow-up period of 66 months (interquartile range, 38-103 months), the rates and median time of progression to muscle invasion were 6.9% and 22.5 months in the PUC group, and 22.9% and 10.0 months in the SUC group. Moreover, the incidence of progression to metastasis was 4.6% and 15.7% in the PUC and SUC groups, respectively. The 5-year PFS rates (64.5% and 81.9%, P < .001) and 5-year OS rates (71.7% and 86.2%, P = .009) were lower in the SUC group than in the PUC group. On multivariate analysis, SUC presence independently predicted progression to muscle invasion and metastasis.

Conclusion: At initial TURBT diagnosis, we must pay more attention to higher progression risk of SUC than that of PUC in nonmuscle-invasive bladder cancer.