Metaplastic carcinomas might display more benign features and less axillary lymph node metastasis than IDC. High signal intensity on T2 MRI images and hormone receptor negativity would be helpful in differentiating this tumor from other breast cancers.

PurposeThe purpose of this study is to evaluate imaging and histopathologic findings including the immunohistochemical characteristics of invasive micropapillary carcinoma (IMPC) of the breast.MethodsTwenty-nine patients diagnosed with IMPC were included in the present study. Mammographic, sonographic, and magnetic resonance imaging (MRI) findings were analyzed retrospectively according to the American College of Radiology Breast Imaging Reporting and Data System lexicon. 18F-fluorodeoxyglucose positron emission tomography-computed tomography (PET-CT) findings were also evaluated. Microscopic slides of surgical specimens were reviewed in consensus by two pathologists with a specialty in breast pathology.ResultsMost IMPCs presented as a high density irregular mass with a non-circumscribed margin associated with microcalcifications on mammography, as an irregular hypoechoic mass with a spiculated margin on ultrasound, and as irregular spiculated masses with washout patterns on MRI. PET-CT showed a high maximum standardized uptake value (SUVmax) (mean, 11.2). Axillary nodal metastases were identified in 65.5% of the patients. Immunohistochemical studies showed high positivities for estrogen receptor and c-erbB-2 (93.1% and 51.7µ, respectively).ConclusionEven though the imaging characteristics of IMPCs are not distinguishable from typical invasive ductal carcinomas, this tumor type frequently results in nodal metastases and high positivities for both estrogen receptor and c-erbB-2. The high SUVmax value that is apparent on PET-CT might be helpful in the diagnosis of IMPC.