Lobular carcinoma of the breast with extracellular mucin: new variant of mucin-producing carcinomas?

The presence of mucin in infiltrating lobular carcinomas has been described as occurring exclusively in an intracytoplasmic location. To the best of the authors' knowledge, infiltrating lobular carcinoma displaying extracellular mucin has not been described in the literature. Herein is presented a case of lobular carcinoma with extracellular mucin in a 60-year-old female patient, who also had a contralateral ductal carcinoma of the cribriform type. Histologically the tumor had the classical appearance of infiltrating lobular carcinoma with signet ring cells and 'Indian file' infiltration of the stroma as well as pools of extracellular mucin. It is of great importance to appropriately classify breast carcinomas as ductal or lobular in origin due to the different treatment, prognosis, and clinical behavior of these lesions. The present finding opens the door for discussion of the current knowledge concerning histological variants of lobular carcinoma and should alert pathologists to the fact that the presence of extracellular mucin in an otherwise classical infiltrating lobular carcinoma does not preclude this diagnosis.