We report the case of a 35-year-old woman who complained of a rapid enlargement of a pre-existing breast mass and yellowish nipple discharge. Clinical examination revealed a firm mass measuring 15 x 10 cm and "peau d'orange" phenomenon. Sonography revealed a well-defined mass with heterogeneous echotexture and hyperechoic trabecular structures that delineated hypoechoic areas, resulting in a honeycomb pattern. The patient underwent a surgical exploration and a biopsy of the mass and of the skin. The histopathologic examination revealed an atypical medullary carcinoma with high mitotic activity.