Urothelial transitional cell carcinoma with endophytic growth patterns: a discussion of patterns of invasion and problems associated with assessment of invasion in 18 cases.

Most papillary transitional cell carcinomas (TCC) are characterized architecturally by an exophytic growth of fingerlike papillae, but some exhibit a prominent endophytic growth pattern resulting in considerable difficulty in assessing invasion. We report on 18 cases of TCC (17 urinary bladder, one pelvicalyceal system) in which endophytic growth was evident either as interanastomosing cords and columns of urothelium, often with a striking resemblance to inverted papilloma (inverted papilloma-like pattern), or as broad, pushing bulbous invaginations into the lamina propria (broad-front pattern). The mean age of the patients was 68 years (range, 32-94 years), with a male preponderance (3.5:1). In four cases, the endophytic pattern was exclusively inverted papilloma-like, 10 cases had only the broad-front pattern, and four cases showed both patterns. Exophytic papillary TCC of the usual type was present in all but two cases, varying from focal (five cases) to moderate (five cases) to extensive (six cases). In spite of the extensive incursion into the lamina propria resulting from the inverted growth, only nine cases (50%) had unequivocal destructive invasion (lamina propria invasion, eight cases; muscularis propria invasion, one case). Follow-up data, available in 14 cases (1-48 months; mean, 15.5 months), revealed one patient alive with disease, 11 patients with no evidence of disease, and two patients dead of other causes. The limited follow-up does not permit evaluation of the impact of the endophytic patterns on outcome. Because the phenomenon of endophytic growth in TCC has received little attention, we present detailed morphologic descriptions of our cases and review the problems associated with assessment of invasion and the different patterns of invasion by TCC.