Accessory breast is a congenital atavism condition. Accessory breast tissue may arise anywhere along the mammary line because of the failure of complete maturation during embryogenesis. The malignancy in accessory breast tissue is considered as primary breast cancer. Axillary breast cancer is an under-recognised site of primary breast cancer. The authors presented a case report of a 52-year-old premenopausal female who presented with axillary immobile mass in her left axilla and who was diagnosed after extensive investigations with Stage II B oestrogen receptor (ER)/progesterone receptor (PR) positive, human epidermal growth factor 2/neu proto-oncogene (HER2/neu) negative, and poorly differentiated accessory breast adenocarcinoma. The patient was designated as Stage II B, and following the 2012 National Comprehensive Cancer Network (NCCN) guidelines for breast cancer management, was surgically treated, followed by postoperative adjuvant chemotherapy in the form of four cycles of doxorubicin and cyclophosphamide (AC protocol), and then four cycles of docetaxel. Subsequently, radiotherapy was given followed by hormone therapy. The patient was followed up for 7 years, and at the time of publication, is alive and stable. Accessory breast cancer is a rare disease and misdiagnosis of these cases is a common problem, leading to extensive and unnecessary investigations; therefore, physicians must be aware of these cases. Management of accessory breast cancer is according to the same guidelines provided for management of the condition. Follow-up data should extensively encourage the determination of the prognosis of accessory breast cancer in comparison to common breast cancer.