XX male with breast cancer.

We present the case of a 66-year-old XX male who developed breast cancer on the left side at the age of 61. His clinical, endocrinological and cytogenetic features are described. The presence of hypospadias and cancer in the left breast are noteworthy; the latter is very rarely found in Klinefelter syndrome patients. An outline of the pathogenesis of breast cancer in XX male patients is also given. This is the first report of an XX male with breast cancer.