Invasive micropapillary carcinoma (IMPCa) of the breast refers to a unique variant of invasive ductal carcinoma, but its biological behavior has not been elucidated well. We analysed 16 IMPCa cases (10 pure type, six mixed type). The incidence of IMPCa was 1.0% of all primary breast carcinoma. High nuclear grade (75.0%), as well as poorly differentiated histological grade (81.3%), was frequently seen. Lymph node metastases were evident in 92.9% of the examined cases, and about half of them showed more than 10 positive nodes. Comparison between serially experienced invasive ductal carcinoma, not otherwise specified (IDC-NOS), revealed that both high nuclear grade and poor histological grade were significantly more frequent (P<0001), there was a lower frequency of positive estrogen receptor/ progesterone receptor (P < 0.05, P < 0.01), a higher frequency of HER-2 overexpression (P < 0.025), and more frequent lymph node metastases (P < 0.05) in IMPCa. The comparison between lymph node positive IDC-NOS did not show any statistically significant differences in frequency for positive p53, matrix metalloproteinase protein-2 (MMP-2), vascular endothelial growth factor (VEGF) or E-cadherin. However, IMPCa showed a significantly increased number of blood vessels counted by CD34 immunostains (P < 0.05). These results suggest that IMPCa is, at least, the same or more aggressive than lymph node positive cases of IDC-NOS. Hence, not only the high incidence of lymph node metastases but also distant, blood-borne metastases may be important.
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