Growth pattern in superficial urothelial bladder carcinomas. Histological review and clinical relevance

The question of when an intraepithelial urothelial carcinoma becomes invasive into the lamina propria of the urinary bladder is an unresolved issue. Our objective was to analyse a series of consecutive superficial carcinomas to assess the importance of growth pattern in tumour recurrence and progression.

The pathological staging of 200 superficial (pTa/pT1) bladder carcinomas was reviewed. Non-invasive lesions and tumours invading the lamina propria were distinguished. Both infiltrating and pushing patterns of growth were regarded as lamina propria invasion.

A total of 35 (17.5%) pTa and 165 (82.5%) pT1 tumours were identified. Among pT1 tumours, 39 (23.6%) displayed the infiltrating pattern of invasion and 126 (76.4%) the pushing pattern. Differences in five-year recurrence-free (P = 0.01) and progression-free (P = 0.001) survival were demonstrated between pTa and pT1 tumours, and between pT1 infiltrating and pT1 pushing subcategories. Invasive growth pattern has a 1.86 times higher risk of tumour recurrence and 3.01 times higher risk of progression.

The pT1 category of bladder carcinoma should include a group of tumours defined by its pushing pattern of growth. Some cases may have been previously considered pTa, but follow an intermediate clinical course between pTa and pT1 tumours with infiltrating growth pattern.