e17018 Background: Second transurethral resection (TUR), which is now recommended for all T1 high-grade bladder urothelial carcinoma, may not be necessary for patients with minimal tumor burden at the first TUR. T1 microstaging by the recognition of the muscularis mucosae or vascular plexus may be one promising method for evaluating tumor burden, but is sometimes technically difficult to assess. The number of TUR chips with tumor invading into lamina propria (T1chips) is easy to assess and can be available for all patients with T1 bladder urothelial carcinoma. Our aim was to determine clinicopathological factors which can predict the existence of residual tumor on the second TUR specimens for T1 high-grade bladder urothelial carcinoma. Methods: A total of 50 patients were diagnosed with T1 high-grade bladder urothelial carcinoma after the first TUR. We performed second TUR for the 50 patients. The median interval from the first and the second TUR was 6 week (range, 2-10). Voided urine cytology was taken in all patients between the first and the second TUR, at least 1 week after the first TUR. The existence of proper muscle tissue was confirmed in all specimens for the first and the second TUR. Tumor size, the number of tumor, the presence of carcinoma in situ (CIS), the number of TUR chips containing lamina propria invasion (T1chips) were recorded for the first TUR specimens. Results: A total of 20 (40%) patients had residual tumor on the second TUR. The second TUR stage was: T0 30 (60%); Ta/is 7 (14%); T1 9 (18%); and T2 4 (8%), respectively. In univariate analysis, positive urine cytology before the first TUR (48% vs 0% in negative), positive urine cytology between the first and second TUR (76% vs 21% in negative), and multiple T1 chips on the first TUR specimens (58% vs 6% in one T1 chip) were associated with residual tumor on the second TUR. In addition, in multivariate analysis, the number of T1 chips on the first TUR and urine cytology between the first and the second TUR were the significant predictors for residual tumor on the second TUR. Of 15 patients with multiple T1 chips and positive urine cytology between the first and the second TUR, 13 (87%) had residual tumor on the second TUR, compared to 0% (0/15) in those with one T1 chip and negative urine cytology between the first and the second TUR. Conclusions: Second TUR may not be necessary for all patients with T1 high-grade bladder urothelial carcinoma. The number of T1 chips on the first TUR and urine cytology between the first and the second TUR are useful factors for predicting second TUR stage.