Synchronous Primary Metastatic Infra-Mammary Accessory Breast Cancer and Ipsilateral Breast Cancer: An Extremely Rare Case Report

<b>Background:</b> Accessory breast cancer cases are rarely reported in the literature. Of the reported cases, the predominantly available ones are those localized in the axillary region. <b>Methods:</b> We present here a very rare case of metastatic accessory breast cancer. It was located in the infra-mammary region (IMR). IMR accessory breast cancer is a rare form of breast cancer. Although ectopic nipples are occasionally found in the IMR, because of the lack of ductal tissue malignant changes, they are rare. <b>Results:</b> In our case, the primary tumor was localized in the congenital accessory breast tissue (ABT). It was recognized as invasive lobular accessory breast cancer cT3N1M0 with a second NST carcinoma, cT2N0M0, Stage IIA, in the ipsilateral breast. A multi-modal approach was applied. Adjuvant chemotherapy was carried out with epirubicin, cyclophosphamide, and paclitaxel, with post-chemotherapy ultrasound followed by right radical mastectomy. Adjuvant radiotherapy was given to our patient in the form of 25 fractions of 50 GY for 25 days, followed by hormonal treatment with Letrozole, 2.5 mg/day, to be continued for 5 years. <b>Conclusions:</b> our case demonstrates that since it is rare to find accessory breast cancer in the infra-mammary region, early identification and management with a multi-modal approach can lead to a successful patient outcome.