부산대학교 도서관

A 50-year-old woman presented with an enlarging left breast mass. We identified a tumor with the maximum diameter of 25 mm in the DC segment of the left breast and diagnosed it as breast cancer T2N0M0 Stage IIA following close exploration. Furthermore, we identified the defect of the pectoralis major and minor muscles on the ipsilateral side. Namely she was associated with congenital defect of the pectoralis muscle. The treatment was preceded by neoadjuvant chemotherapy. The tumor showed a decrease in size on imaging, thereby we performed left mastectomy and sentinel lymph node biopsy. When the left breast was removed, the pectoralis major muscles (in sternocostal area and abdomen) and the pectoralis minor muscles were lacked and the ribs, intercostal muscle and serratus anterior muscle were exposed. However, we safely pursued the operation. Her postoperative course was uneventful and she was discharged from our hospital on the 6th hospital day. There were no histologic cancer remnants. It is believed that one in approximately 20,000 people has congenital defect of the pectoralis muscle. We report a case of breast cancer developed on the affected side of this anomaly which is extremely rare.