Multicentric Breast Cancer of the Axillary and Pectoral Breasts: A Case Report and Literature Review.

Multicentric cancer of the pectoral and ectopic breasts is extremely rare, and diagnosing this malignancy remains challenging because axillary breast cancer is easily misdiagnosed as lymph node metastasis. Moreover, there are no established treatment guidelines for this disease. We present our experience with a multicentric breast cancer patient who showed different responses to neoadjuvant chemotherapy (NAC) and underwent surgical treatments that differed from those in previous studies. In our case, the preoperative imaging of both lesions and subsequent core needle biopsy of each lesion were crucial, as these procedures confirm the diagnosis and help decide the chemotherapy regimen based on the subtype. After NAC, the patient underwent right breast-conserving surgery, sentinel lymph node biopsy (SLNB), and excision of accessory breast tissue in the right axilla. SLNB should be the initial step in staging multicentric breast cancer, unless imaging scan shows evidence of lymph node metastasis.