Case of second primary breast cancer in ectopic breast tissue and review of the literature.

Accessory breast tissue (ABT) is found in approximately 2%-6% of the female population and are subject to most of the physiological and pathological changes that occur in pectoral breast. Primary breast cancer occurring in ABT is a rare occurrence and a second primary breast cancer occurring in an accessory breast has never been reported. We report the case of a 60-year-old woman with a history of mastectomy for left breast cancer 5 years prior to presentation, who presented with an enlarging right axilla mass found to be a second primary breast cancer in an accessory tissue on biopsy. Many physicians are unfamiliar with the clinical presentation of accessory breast cancer due to the rarity of the condition and this ultimately results in delayed diagnosis and advanced disease at presentation. It is therefore prudent that physicians have a high index of suspicion when patients present with axillary masses. © BMJ Publishing Group Limited 2021. No commercial re-use. See rights and permissions. Published by BMJ.