OBJECTIVETo investigate the relationship between lymph node metastasis and pathologic features of invasive micropapillary carcinoma (IMPC) of the breast.

METHODSHistopathologic features and status of lymph node metastasis of fifty-one cases of IMPC were studied by microscopic examination, immunohistochemical staining (VEGF-C and VEGFR-3) and analysis of lymphatic vessel density.

RESULTS(1) The number of positive lymph nodes in histologic grade II/III IMPCs was significantly higher (mean 12.5) than that in histologic grade I tumors (mean 4.0). (2) The incidence of nodal metastases in IMPCs with lymphocyte infiltration (+)/(++) was significantly higher (27/28, 96.4%) than that in tumors with no or minimal lymphocyte infiltration (-)/(+/-) (14/23, 60.9%), and the number of positive nodes was also higher (mean 14.4) in tumors with lymphocyte infiltration compared with those without (mean 4.6). (3) In IMPCs with histologic grade II/III, the expression of VEGF-C was significantly higher than that of histologic grade I tumors (P = 0.03). VEGF-C expression was in positive correlation with lymph node metastasis (P = 0.006) and lymphatic vessel density (P = 0.009). Lymph node metastasis was also correlated with lymphatic vessel density (P = 0.007). (4) The percentage of IMPC component in the tumor did not correlate with nodal metastasis. The metastatic foci in lymph node were all IMPC or mainly IMPC. (5) Fourteen of twenty-eight cases (14/28, 50%) of IMPC containing ductal carcinoma in-situ (DCIS) were DCIS of micropapillary type.

CONCLUSIONSThe histologic grade, lymphatic vessel density and lymphocyte infiltration are key histological features that are correlated with lymph node metastasis of IMPC. The expression of VEGF-C and VEGFR-3 may play an important role in the development of lymph node metastasis of IMPC. Micropapillary type DCIS may be the early stage of IMPC.