Lobular carcinoma of the breast in a patient with Klinefelter's syndrome. A case with bilateral, synchronous, histologically different breast tumors.

A case of bilateral breast cancer in a patient with a Klinefelter mosaic syndrome is presented. The tumor in the left breast was an infiltrating lobular carcinoma with characteristic in situ component. To the knowledge of the authors, this is the first case in the English literature of lobular carcinoma of the breast in a phenotypic man. In fact, it was the pathologic diagnosis which led to the study of the chromosomal abnormality.