Accessory breast tissue, or polymastia, is a developmental variation whereby abnormal breast tissue is found in addition to the normal breasts, and is often not detected until puberty. To varying degrees, this can affect 2-6% of women and 1-3% of men; most commonly, this occurs as solitary accessory nipples without associated breast tissue.
Accessory breast tissue can be found anywhere along the “mammary lines”, extending from the armpits to the normal chest nipples, and downwards to the groin or inner thigh. Changes or symptoms may be noticed during puberty, at different times of the menstrual cycle, or during pregnancy and breastfeeding.
Breast cancer can rarely occur in accessory breast tissue, particularly if the tissue is larger and more developed. If you notice any symptoms, such as swelling and tenderness, or restriction in the range of arm motion, or are otherwise concerned, you should see your doctor. Symptomatic accessory breast tissue can be removed surgically if required.