OBJECTIVETo clarify the relationship between biologic behavior and morphologic features of invasive micropapillary carcinoma (IMPC) of the breast.

METHODSTwo thousand and eighty-eight cases of clinically defined monocentric breast cancer without pre-operative biopsy (except fine needle aspiration procedure) were examined by whole mammary gland serial sectioning. The clinicopathologic and morphologic features (including microscopic and ultrastructural) of IMPC were analyzed.

RESULTSOne hundred and seventeen cases of IMPC (6.2%, 117/1 880) were diagnosed during the period of study. The incidence of lymphovascular invasion (54.7%, 58/106) and nodal metastases (76.4%, 81/106) was significantly higher in IMPC, as well as the number of metastatic node (on average 9.6) was significantly more in IMPC, as compared with that of the invasive ductal carcinoma. Microscopically, the tumor was characterized by morula-like clusters and small papillae of malignant cells floating within irregular interstitial spaces and separated by fibrous septa. Ultrastructurally, microvilli were observed on the neoplastic cell surface at the periphery of the micropapillae. There were also numerous fine intermediate filaments in the cytoplasm. Newly formed capillaries were noted in the interstitium and some tumor cells were directly in contact with endothelial cells.

CONCLUSIONSA predominant component of IMPC in breast carcinoma is associated with a higher risk of lymphovascular invasion and nodal metastasis. The aggressive behavior of IMPC can be attributed to the proliferative activity of the tumor cells, and its associated angiogenesis.