I've noticed a bloody discharge from the nipple.

This can be significant. But first it is necessary to be sure that it is really blood and not a glandular secretion. Therefore, the fresh discharge from the nipple is put onto a slide and looked at under the microscope. If it contains red blood cells, then it is blood.

Bloody discharges can come from excessive growth of normal or exuberant tissue in the breast ducts; this is an innocent phenomenon. Or it can be the first symptom of tumor or cancer, which is sometimes too small even to be felt. Usually a biopsy is required to make an accurate diagnosis.