Purpose To evaluate the prognosis of patients with pT1 bladder cancer who underwent en bloc resection of bladder tumors (ERBTs), stratified by invasion to the muscularis mucosa (MM) level. Methods Among 64 specimens obtained by ERBT with bipolar energy from patients with pT1 bladder cancer, MM was detected in 61 specimens. Thus, 61 specimens were included in this retrospective study. Patients were stratified by invasion to the MM level (pT1a, invasion above the MM level; pT1b, invasion within the MM level; and pT1c, invasion beyond the MM level). In specimens with discontinuous MM, invasion to the MM level was predicted from the dispersed MM in the specimen. The primary endpoints were progression-free survival (PFS) and cancer-specific survival (CSS). Results Progression occurred in 2/39 patients with pT1a (5.1%), 1/6 patients with pT1b (16.7%), and 6/16 patients with pT1c cancer (37.5%). Cancer death occurred in 1/39 patients with pT1a (2.6%), 0/7 patients with pT1b, and 3/16 patients with pT1c cancer (18.8%). Patients with pT1a or pT1b cancer had a significantly better prognosis than those with pT1c cancer. On univariate analysis, tumor size >= 3 cm and pT1c were significantly associated with shorter PFS. On multivariate analysis, only pT1c was independently associated with shorter PFS. Conclusion This is the first study evaluating the prognosis by T1 substaging based on invasion to the MM level using ERBT specimens. ERBT provided high-quality specimens for diagnosing the MM and showed poor prognosis in pT1c bladder cancer. ERBT could be an appropriate surgical approach for an accurate diagnosis and prognosis of the T1 bladder cancer substage.
