Ectopic breasts usually develop along the mammary ridges. Their incidence has been reported as up to 5-6%. Development of malignancy is rare. We report three cases of postmenopausal female patients with breast cancer which developed in the axillary accessory breast. They were all successfully treated by surgery and adjuvant therapy. A review of the literature on the incidence and pathology of ectopic mammary tissue is also presented.