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In order of increasing frequency, the following are the commonest causes of nipple discharge in the non lactating breast: carcinoma, intraductal papilloma, and mammary dysplasia with ectasia of the ducts. The important characteristics of the discharge and some other factors to be evaluated by history and physical examination are as follows:
• Nature of discharge (serous, bloody, or other).
• Association with a mass or not.
• Single duct or multiple duct discharge.
• Discharge is spontaneous (persistent or intermittent) or must be expressed.
• Discharge produced by pressure at a single site or by general pressure on the breast.
• Relation to menses.
• Premenopausal or postmenopausal.
• Patient taking contraceptive medicines or estrogen.

Unilateral, spontaneous serous or serosanguineous discharge from a single duct is usually caused by an intraductal papilloma or, rarely, by an intraductal cancer. In either case, a mass may not be palpable. The involved duct may be identified by pressure at different sites around the nipple at the margin of the areola. Bloody discharge is more suggestive of cancer but is usually caused by a benign papilloma in the duct. Cytologic examination may identify malignant cells, but negative findings do not rule out cancer, which is more likely in women over age 50. In any case, the involved duct-and a mass if present- should be excised. Ductography may identify a filling defect prior to excision of the duct system.

In premenopausal women, spontaneous multiple duct discharge, unilateral or bilateral, most marked just before menstruation, is often due to mammary dysplasia. Discharge may be green or brownish. Papillomatosis and ductal ectasia are usually seen on biopsy. If a mass is present, it should be removed.

Milky discharge from multiple ducts in the nonlactating breast occurs in certain endocrine syndromes, presumably as a result of increased secretion of pituitary Prolactin. Serum Prolactin and TSH levels should be obtained to search for a pituitary tumor or hypothyroidism. Phenothiazines and contraceptive medicines may also cause milky discharge that ceases on discontinuance of the medication.