~10% of the time. Bloody nipple discharge is usually secondary to a benign tumor or chronic inflammation within the duct, with breast cancer a distant third. Any woman with bloody discharge requires breast evaluation, which will include a diagnostic mammogram+/-ultrasound, physical examination, and nipple aspiration cytology. If the results remain equivocal, a surgical biopsy (terminal duct excision) may be done.
It can be. Nipple bleeding requires check up for breast cancer. Occasionally it is caused by a benign papilloma in the milk ducts but you can not be sure without further testing, which should be done by a breast cancer specialist...Usually a good surgeon.
One possibility. Cancer is certainly one of the possible causes of bloody nipple discharge. A more common cause, however, is a polyp-like growth inside one of the breast ducts called a papilloma. It would be a good idea to see a breast surgeon to talk with you about additional test you may need to sort this out.