Female type cystic hyperplasia in a male breast

A 28 year old man had a swelling of the right breast. He was phenotypically and karyotypically a normal male. Microscopic examination of the excised specimen showed the pattern of cystic hyperplasia identical to that commonly seen in the female breast. Numerous cysts were grouped in a lobular pattern and their lining showed apocrine metaplasia. There was extensive background fibrosis, some mammary duct ectasia and some features consistent with the more classical microscopic appearances of gynaecomastia. Whilst some of the features noted above are sometimes seen in gynaecomastia the presence of the full range of the features of cystic hyperplasia is distinctly unusual in the male.