Invasive Micropapillary Carcinoma of the Breast: A clinicopathologic study of 16 cases

ABSTRACT

Invasive micropapillary carcinoma is a recently defined unusual variant of invasive breast carcinoma characterized by the formation of micropapillae within clear spaces separated by delicate fibrocollagenous stroma. This study was designed to examine clinicopathologic features of invasive micropapillary carcinoma of the breast. Sixteen cases of invasive micropapillary carcinoma were retrieved from the files of the Department of Pathology, Yeungnam University College of Medicine. We evaluated their clinicopathologic findings including patients' age, tumor size, nuclear grade, vascular invasion, axillary lymph node status, presence of extensive intraductal carcinoma, estrogen and progesterone receptors, p53, c-erbB-2, MIB-1 labelling index and follow-up data and compared this results with those of 292 cases of invasive ductal carcinoma, not otherwise specified. The incidence of invasive micropapillary carcinoma was 4.2% of all invasive breast carcinoma, and the mean age of the patients was 46 years. Nine cases were pure form (over 75% of micropapillary growth pattern in the tumor) and seven cases were mixed form. The results of clinicopathologic findings, except vascular invasion and axillary lymph node status, of the 16 cases of invasive micropapillary carcinoma were not different from those of the 292 cases of invasive ductal carcinoma, not otherwise specified (p>0.05). However, the rate of vascular invasion and axillary lymph node metastasis was significantly higher in invasive micropapillary carcinoma (p <0.05). Of 16 cases, five cases had distant metastasis during follow-up period, and one patient died of cancer. Although the mechanism of higher vascular invasion and lymph node metastasis in micropapillary growth pattern could not be determined, we propose that invasive micropapillary carcinoma should be recognized as a separate entity with increased risks of vascular invasion and axillary lymph node metastsis.