Muscularis mucosa differentiates two populations with different prognosis in stage T1 bladder cancer

Contrary to previous belief, the existence of a muscularis mucosa in the human urinary bladder has now been well described. Although the degree of development of this structure seems variable, it can frequently be used to differentiate two levels within the subepithelial connective tissue: the lamina propria and the submucosa. The present study evaluates whether this morphologic feature is potentially useful for the identification of two populations with Stage T1 bladder cancer: those with tumor invasion confined to the lamina propria (pT1A) and those with tumors infiltrating into the submucosa (pT1B).

A series of 170 Stage T1 papillary bladder tumors was analyzed pathologically to identify the level of subepithelial connective tissue invasion. Both the reproducibility of such a differentiation and its prognostic implication were evaluated using Kaplan-Meier survival estimates and the Cox regression model.

In specimens from transurethral resection, categorization into T1A or T1B could be performed in 98 of 170 cases (58% of specimens). Such differentiation proved to be of prognostic value with significantly different 5-year survivals between the two subcategories (pT1A [n = 50] vs pT1B [n = 49]) (log-rank, P < 0.02). Cox's regression analysis of pT1 subcategory and grade was performed in the 99 cases in which the differentiation between pT1A/pT1B could be made. This demonstrated that the depth of subepithelial connective tissue invasion was an independent prognostic factor (P < 0.05).

The depth of tumor infiltration can be assessed in a considerable proportion of Stage T1 bladder neoplasms. The present study validates the prognostic significance of such a distinction both by Mantel-Haenszel life table method and Cox's regression analysis.