Biological distinction between grades 2 and 3 with respect to intravesical recurrence in T1 high-grade bladder tumors: a retrospective study

Background The pathological grading system for non-muscle-invasive bladder cancer is based on the WHO 2004/2016 classification system (low-grade: LG/high-grade: HG) and the WHO 1973 classification system (Grade 1: G1/Grade 2: G2/Grade 3: G3). Recently, the usefulness of combining both systems and classifying the tumors as LG/G1, LG/G2, HG/G2, and HG/G3 has been demonstrated. In this study, we compared the prognosis of intravesical recurrence in relation to different treatment intensities between HG/G2 and HG/G3 bladder cancers. Methods We retrospectively evaluated the clinical and therapeutic outcomes of 145 patients diagnosed with T1 HG bladder cancer between 2000 and 2020. We classified 145 patients into three groups: (1) patients with T1 HG/G2 and HG/G3 who received intravesical instillation therapy (n = 76), (2) patients with T1 HG/G2 who did not receive intravesical instillation therapy (n = 32), and (3) patients with T1 HG/G3 who did not receive intravesical instillation therapy (n = 37). Results The median intravesical recurrence-free survival for all patients was 34.2 months. The number of tumors, the presence of intravesical instillation therapy, and tumor grade were significant prognostic factors for intravesical recurrence in all cases. Groups 2 and 3 showed significantly worse prognosis than group 1 in the multivariate analysis. Conclusions Regarding intravesical recurrence, intravesical instillation therapy is necessary for both T1 HG/G3 and T1 HG/G2 bladder cancers.