Background: We evaluated the clinical outcome of low grade Ta bladder cancer followed-up for a long period using the 2004 WHO grading system. Methods. We retrospectively reviewed 190 patients with primary, low grade Ta bladder cancer. We defined worsening progression (WP) as confirmed high grade Ta, all T1 or Tis/concomitant CIS of bladder recurrence, upper urinary tract recurrence (UTR), or progression to equal to or more than T2. The associations between clinicopathological factors and tumor recurrence as well as WP pattern were analyzed. We also evaluated the late recurrence of 76 patients who were tumor-free for more than 5 years. Results: Tumor recurrence and WP occurred in 82 (43.2%) and 21 (11.1%) patients during follow-up (median follow-up: 101.5 months), respectively. WP to high grade Ta, all T1 or Tis/concomitant CIS was seen in 17 patients, and UTR and progression to equal to or more than T2 were seen in 2 and 2 patients, respectively. Multivariate analyses demonstrated that multiple tumor (p < 0.001, HR: 2.97) and absence of intravesical instillation (IVI) (p < 0.001, HR: 2.88) were significant risk factors for tumor recurrence while multiple tumor was the only risk factor for WP (p = 0.001, HR: 5.26). After a 5-year tumor-free period, 9 patients experienced late recurrence in years 5 and 10 and were diagnosed at a follow-up cystoscopy, however, only 2 patients recurred beyond 10 years and were found by gross hematuria. There were no significant risk factors of late recurrence. Conclusions: Multiple tumor was a risk factor for both tumor recurrence and WP while IVI did not affect the occurrence of WP. Our results suggest that routine follow-up of patients with low grade Ta bladder cancer is needed up to 10 years from the initial diagnosis.
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