from the American College of Radiology
"Nipple discharge is a common complaint that leads patients to breast imaging evaluation. At least 80% of women will experience at least 1 episode of nipple discharge during their reproductive years. Nipple discharge is the third most common breast complaint after breast pain and breast mass, with a prevalence of 4.8% to 7.4%, and accounts for 5% of all breast symptoms. It is categorized as physiologic or pathologic.
Pathologic nipple discharge tends to be unilateral, from a single duct orifice, spontaneous, and serous or bloodstained. Nipple discharge that exhibits any one of these features may be considered pathologic.
Physiologic nipple discharge tends to be bilateral, from multiple duct orifices, and white, green, or yellow in color. In a study by Goskel et al, nonspontaneous nipple discharge, which was frequently colored or milky, was differentiated from spontaneous nipple discharge, which was considered pathologic. In this study, none of the patients with nonspontaneous nipple discharge developed cancer on follow-up examination. In another study by Bahl et al, no in situ or invasive cancers were found in patients whose nipple discharge did not exhibit any of the pathologic features. If patient history and physical examinations demonstrate physiologic nipple discharge and routine screening mammography is up to date, no radiologic investigation is needed.