After intraductal papilloma, unilateral bloody nipple discharge from one duct orifice is most commonly caused by which of the following pathologic conditions?

B. Intraductal carcinoma.

DISCUSSION: Nipple discharge is surgically significant when it is grossly bloody and when it appears at a single duct orifice on one nipple. Bloody discharge is usually due to a benign intraductal papilloma; however, intraductal carcinoma in the large ducts under the nipple can be the cause of bloody discharge, and pathologically the lesion is frequently a large papillary tumor that has become malignant. Paget's disease of the nipple is also due to intraductal carcinoma arising in subareolar ducts, but it rarely is associated with nipple discharge. Subareolar mastitis may produce nipple discharge, but it is purulent and not bloody. Inflammatory carcinoma is not associated with nipple discharge.