Gynaecomastia, male breasts. Gynaecomastia is usually due to abnormally high levels of the female hormone oestrogen in the blood. Many conditions can cause this, such as liver cirrhosis (where the liver cannot break down the natural oestrogen present), tumours (usually involving the testes, adrenal glands, pituitary, lung and liver) and certain medications. Treatment therefore depends on the underlying cause. The swelling often subsides naturally, although breast reduction surgery can also be performed. Here, the excess of oestrogen has arisen from a course of anti-androgen drugs, used to treat prostate cancer.