Several of the hormonal drugs that are sometimes used to treat prostate cancer may cause breast enlargement. The breast enlargement is a result of hormonal effects on the male breast tissue and is not a sign of prostate cancer spreading to the breasts.

These drugs include flutamide, bicalutamide, stilboestrol, leuprolide and goserelin (although breast enlargement is uncommon with the last two drugs).

Sometimes the breast enlargement can cause discomfort or pain.

The risk of developing this complication, called gynaecomastia, can be reduced by giving radiotherapy to both breasts before the drug is started. This only needs one treatment, as an outpatient, with only a small dose of radiation. There are virtually no side effects, other than slight redness for a short time in some men.

The radiotherapy is usually given before the hormone drugs are started or within the first few weeks after starting. Radiotherapy will not reverse gynaecomastia once it has developed.