Which kinds are harmless
White, yellow or green discharge that comes from both breasts, from many ducts, and only on squeezing is usually hormonal in origin. A raised prolactin level and thyroid disorders are common causes of this picture, and its link to cancer is rare.
The discharge that needs investigation
Discharge from one breast, from a single duct, appearing on its own — that is, without squeezing — is assessed differently. Bloody, clear watery or brown discharge in particular must be investigated.
The most common cause of this kind of discharge is an intraductal papilloma: a benign, wart-like growth inside a milk duct. Rarely, cancer can also announce itself this way.
Diagnosis and treatment
Alongside examination, ultrasound and — depending on age — mammography are used; some patients need further imaging.
Treatment is the removal of the duct the discharge comes from, through a small incision. This is both diagnosis and treatment: the tissue removed goes to pathology, and the discharge stops.