Invasive Micropapillary Carcinoma of the Breast: A Clinicopathologic Study of 103 Cases of an Unusual and Highly Aggressive Variant of Breast Carcinoma

Invasive micropapillary carcinoma (IMPC) of the breast is an uncommon, highly aggressive breast cancer that may occur in pure and mixed forms. Our aim in this study is to investigate the relationship between clinical, histopathologic, and immunohistochemical features of pure and mixed IMPC cases diagnosed and treated at our institution. One hundred and three IMPC cases diagnosed at our institution over a period of 19 years have been selected. Clinical, histopathologic features, as well as hormone status and c‐erb‐B2 overexpression of tumors were re‐evaluated. Mann–Whitney U, chi‐squared, Kaplan–Meier, and Fisher's exact tests were used for statistical analyses. Results were considered to be significant at p < 0.05. Twenty cases (19.4%) were pure, and 83 cases (80.6%) were mixed IMPC. The most common nonmicropapillary invasive carcinoma component in mixed cases was invasive ductal carcinoma (IDC; 78.3%). Progesterone receptor was significantly less positive in pure IMPC cases (p = 0.031). There was no statistically significant difference between the two groups, in terms of mean age of the patients (53.0 versus 52.8), mean tumor size (26.6 mm versus 27.7 mm), presence of high‐grade tumor (p = 0.631), presence of sentinel lymph node (SN) metastasis (p = 1.000), axillary lymph node metastasis (p = 1.000), lymphatic invasion (p = 1.000) and blood vessel invasion (p = 0.475), c‐erbB‐2 overexpression of tumor cells (p = 0.616), distant metastasis (p = 0.549), or overall survival (p = 0.759). The local recurrence rate of the two groups was not statistically significant either (16.7% versus 4.3%). However, local recurrence was detected 12% more commonly (p = 0.100), and ~8 months earlier (p = 0.967) in pure IMPC cases, compared to mixed cases. In addition, presence of local recurrence was found to be statistically significantly associated with estrogen receptor (ER) status (p = 0.004), progesterone receptor (PR) status (p = 0.001), and c‐erb‐B2 overexpression (p = 0.016) in all patients. Overall survival rate was significantly associated with ER staining of the tumor (log‐rank = 0.028). Our findings suggest that hormone receptor negativity may explain the more aggressive behavior of pure IMPC compared to mixed cases. Besides, longer survival period of patients with ER positivity, and the relationship of hormone status and c‐erb‐B2 overexpression and local recurrence further support favorable prognostic value of hormone receptors in invasive breast cancer.