Substaging of T1 bladder carcinoma based on the depth of invasion as measured by micrometer: A new proposal

Background: A significant number of T1 bladder carcinoma patients are understaged by transurethral resection of the bladder (TURB), indicating a substantial need for more accurate staging.

Methods: The authors studied 55 patients with T1 bladder carcinoma detected by TURB at the Mayo Clinic between December 1979 and July 1984. The mean age of the patients was 66 years (range, 50-78 years). All patients were treated by cystectomy. The median interval from TURB to cystectomy was 10 days. Grading was performed according to the 1998 World Health Organization/International Society of Urologic Pathology grading system. The 1997 TNM classification was used for pathologic staging. In addition, the depth of invasion was measured from the mucosal basement membrane by micrometer. Receiver operating characteristic (ROC) analysis was used to evaluate the usefulness of depth of invasion as a marker for advanced stage bladder carcinoma (>/= T2).

Results: The final pathologic stages were Ta (2 patients), T1 (10 patients), T2a (9 patients), T2b (13 patients), T3 (11 patients), and T4 (10 patients) at cystectomy. There was a significant correlation between the depth of invasion at TURB and the final pathologic stage (Spearman correlation coefficient = 0.63; P < 0.001). The overall accuracy for the prediction of advanced stage (>/= T2) bladder carcinoma as measured by the area under the ROC curve was 0.89 (standard error, 0.05). Using 1.5 mm as a threshold (with >1.5 mm indicating advanced stage disease), the sensitivity, specificity, and positive and negative predictive values were 81%, 83%, 95%, and 56%, respectively. Histologic grade at the time of TURB also was associated significantly with final pathologic stage at cystectomy (P = 0.03) whereas stratification of patients according to invasion above or below the muscularis mucosae at TURB was not a significant predictor of final pathologic stage.

Conclusions: The results of the current study show that substaging of T1 bladder carcinoma according to the depth of invasion (as measured by micrometer) provides significant prognostic information. Therefore the authors recommend that it be reported in specimens obtained by TURB.