Micropapillary Mucinous Breast Carcinoma: An Underrecognized Variant

Summary: Invasive micropapillary carcinoma of the breast is a subtype with high malignant potential characterized by lymphovascular invasion (LVI) and a predilection for axil- lary lymph node (AXLN) metastases. In contrast, pure mucinous breast carcinoma (MBC) is relatively indolent with low metastatic potential. Recent studies have described a histologic variant of breast cancer that displays combined mucinous and micropapillary patterns, ie, micropapillary variant of mucinous carcinoma (MpVMBC). This underrecognized variant is, as yet, incompletely characterized clinicopathologi- cally. Extant reports suggest a more aggressive lesion than pure MBC with greater propensity for both LVI and AXLN metastases. Here we present our institution’s experience with MpVMBCs including clinicopathologic and immunohistochemical (IHC) analyses. Greater awareness and recognition of this variant could positively contribute to patient care by (1) avoiding underestimation of malignant potential for individuals whose tumors may have been diagnosed as simply “MBC, not otherwise specified”, and (2) recommending a postsurgical adjuvant approach emphasizing the hormone receptor targets, even perhaps in younger women presenting with AXLN positive disease.