Clinicopathological significance of invasive micropapillary carcinoma component in invasive breast carcinoma

Invasive micropapillary carcinoma (IMP) of the breast is a rare variant of invasive breast carcinoma and most cases of IMP are associated with nodal metastasis and lymphatic invasion. Lesions composed of an IMP component alone are rare and almost always coexist with other pathological components. However, few reports have documented IMP along with its proportion and the coexistent pathological type. We analyzed the total 486 breast cancer lesions operated in our hospital in 1998. We classified the lesions into five groups by the proportion of the IMP component in each lesion. Then we evaluated the incidence of nodal metastasis and lymphatic invasion in each group. The incidence of the invasive carcinoma containing any IMP components was 8.4%. The incidence of nodal metastasis and lymphatic invasion in lesions with an IMP component were significantly higher than that in those with no IMP. No correlation was seen between the incidence of nodal metastasis and the coexistent pathological type, shape of tumor clusters, nuclear grade and the expression of estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2 and gross cystic disease fluid protein-15 in IMP components. The presence of IMP components was a significant predictive factor for nodal metastasis, even if it is detected in only a small proportion of the tumor.