A Rare Presentation of an Invasive Ductal Carcinoma of Ectopic Axillary Breast Tissue

Ectopic breast tissue (EBT) is a rare entity and can present anywhere along the milk line, including the axilla, inframammary region, thighs, perineum, groin, and vulva. However, the axilla is the most common area of presentation. EBT can present as supernumerary breasts or aberrant breast tissue. Malignancy arising in EBT is rare, but the most common morphological variant is invasive ductal carcinoma. We report a case of a 43-year-old woman, a smoker with a family history of breast cancer, who presented to our clinic with a small mass in the right axillary area. After monitoring it for one year, the mass increased in size, so she returned to the clinic and decided with her care team to excise the mass. Histopathology showed invasive mammary adenocarcinoma arising in EBT and was diagnosed as right accessory stage I breast cancer. This case illustrates the imperative that any mass in the axillary region should be thoroughly assessed to rule out carcinoma in the accessory axillary tissue for timely management.