Prognosis of Primary Papillary Ta Grade 3 Bladder Cancer in the Non-muscle-invasive Spectrum

Abstract

Background: Ta grade 3 (G3) non-muscle-invasive bladder cancer (NMIBC) is a relatively rare diagnosis with an ambiguous character owing to the presence of an aggressive G3 component together with the lower malignant potential of the Ta component. The European Association of Urology (EAU) NMIBC guidelines recently changed the risk stratification for Ta G3 from high risk to intermediate, high, or very high risk. However, prognostic studies on Ta G3 carcinomas are limited and inconclusive.

Objective: To evaluate the prognostic value of categorizing Ta G3 compared to Ta G2 and T1 G3 carcinomas.

Design, setting, and participants: Individual patient data for 5170 primary Ta-T1 bladder tumors from 17 hospitals were analyzed. Transurethral resection of the tumor was performed between 1990 and 2018.

Outcome measurements and statistical analysis: Time to recurrence and time to progression were analyzed using cumulative incidence functions, log-rank tests, and multivariable Cox-regression models with interaction terms stratified by institution.

Results and limitations: Ta G3 represented 7.5% (387/5170) of Ta-T1 carcinomas of which 42% were classified as intermediate risk. Time to recurrence did not differ between Ta G3 and Ta G2 (p = 0.9) or T1 G3 (p = 0.4). Progression at 5 yr occurred for 3.6% (95% confidence interval [CI] 2.7-4.8%) of Ta G2, 13% (95% CI 9.3-17%) of Ta G3, and 20% (95% CI 17-23%) of T1 G3 carcinomas. Time to progression for Ta G3 was shorter than for Ta G2 (p < 0.001) and longer than for T1 G3 (p = 0.002). Patients with Ta G3 NMIBC with concomitant carcinoma in situ (CIS) had worse prognosis and a similar time to progression as for patients with T1 G3 NMIBC with CIS (p = 0.5). Multivariable analyses for recurrence and progression showed similar results.

Conclusions: The prognosis of Ta G3 tumors in terms of progression appears to be in between that of Ta G2 and T1 G3. However, patients with Ta G3 NMIBC with concomitant CIS have worse prognosis that is comparable to that of T1 G3 with CIS. Our results support the recent EAU NMIBC guideline changes for more refined risk stratification of Ta G3 tumors because many of these patients have better prognosis than previously thought.

Patient summary: We used data from 17 centers in Europe and Canada to assess the prognosis for patients with stage Ta grade 3 (G3) non-muscle-invasive bladder cancer (NMIBC). Time to cancer progression for Ta G3 cancer differed from both Ta G2 and T1 G3 tumors. Our results support the recent change in the European Association of Urology guidelines for more refined risk stratification of Ta G3 NMIBC because many patients with this tumor have better prognosis than previously thought.

Keywords: Bladder; Cancer; Carcinomas; G3; Grade; Non–muscle-invasive; Stage Ta; Urothelial; World Health Organization.