Lymphovascular Invasion in Micropapillary Urothelial Carcinoma: A Study of 22 Cases

CONTEXT: Micropapillary urothelial carcinoma (MPUC) is a known aggressive variant of urothelial carcinoma. However, the reasons for its aggressiveness remain unclear. OBJECTIVE: To investigate the frequency of lymphovascular invasion in 22 cases of MPUC. DESIGN: Consecutive tissue sections were stained with D2-40 and CD34 to highlight lymphovascular channels associated with MPUC. Spaces containing tumor cells were scored as positive for lymphovascular invasion if the staining pattern on immunohistochemistry was distinct and circumferential. RESULTS: Of 22 cases, 21 (95%) had lymphovascular invasion on immunohistochemical staining, with 91% lymphatic invasion and 4% vascular invasion. Interestingly, 8 cases were originally signed out as negative for lymphovascular invasion on the basis of hematoxylin-eosin-stained sections; of these, 7 (88%) had focal lymphovascular invasion evident on immunohistochemical staining. CONCLUSIONS: Our results confirm that micropapillary lacunae are not lymphovascular channels. However, nearly all MPUC tumors (95% in this series) have evidence of lymphovascular invasion by immunohistochemical analysis. Our data support the use of micropapillary features as a morphologic marker for lymphovascular invasion and MPUC as an adverse histologic type of urothelial carcinoma.