Cytologic Findings in Infiltrating Micropapillary Carcinoma and Mucinous Carcinomas with Micropapillary Pattern

Abstract

To examine the observation that some mucinous carcinomas have a micropapillary pattern and are mucinous variants of the highly angioinvasive infiltrating micropapillary carcinomas (IMPC).We evaluated cytologic findings of 13 IMPC and 55 mucinous carcinomas for comparative features.In mucinous carcinomas, 37 of 50 (74%) had a micropapillary pattern. This group included 27 cases with pure mucinous micropapillary morphology (MUMPC), 8 MUMPC associated with a ductal carcinoma of the IMPC type (MUIDC) and 2 cases of mixed mucinous carcinomas with an MUMPC and a solid variant ofpapillary carcinoma (SVPC) component. On cytology both IMPC and mucinous carcinomas with micropapillary pattern demonstrated the micropapillary pattern, that is, angulated clusters or abortive papillae and ball-like clusters. However, the IMPC smears revealed numerous singly scattered tumor cells and larger fragments with shrub-like branching and the MUMPC had psammoma bodies. The mixed MUMPC and SVPC showed the classic cytologic features of MUMPC admixed with abundant singly dispersed tumor cells in the background representing the SVPC component.Although IMPC and the MUMPC share the micropapillary pattern on histologic examination, mucin alters the appearances in aspirates. Recognition of this morphologic spectrum will help in understanding the behavior of these tumors.