Primary Breast Carcinoma Arising from Ectopic Breast Tissue in the Groin of a Male Patient

Introduction : Breast carcinoma originating from ectopic breast tissue (EBT) in men is a rare event. It may occur anywhere in the so-called milk line, with preference to the axilla, followed by the area immediately inferior to the normal breast. Additionally, it is presumed that EBT has an increased rate of malignant progression, when compared with normal breast tissue. In fact, benign and malignant tumors, such as epithelial, stromal or fibro-epithelial neoplasms, may arise from EBT. Presentation of Case: Here we describe a case of a 45-year old male who presented with a erythematous-brownish skin plaque located at his left groin. An incisional biopsy followed by a routine hematoxylin-eosin study revealed invasive neoplastic epithelial proliferation with obvious glandular differentiation extending from deep subcutaneous tissue to the superficial dermis. Lymphatic invasion was easily observed and the mitotic count was low (1 mitotic figure per square mm). Immunohistochemical staining showed neoplastic cells positive for estrogen receptor, progesterone receptor, gross cystic disease fluid protein 15 (GCDFP15) and mammaglobin, conforming a low-grade ductal infiltrating carcinoma (invasive mammary carcinoma of no special type). Conclusion: To our knowledge, this is the first report in the literature of a breast carcinoma originating from EBT in a male patient outside the thoracic region. Clinicians must be aware of EBT tumors to any lesion occurring in the milk line.