Borderline phyllodes tumor arising in accessory breast tissue at the axilla

Accessory breast tissue is an anatomical variation which occurs during embryogenic development. It appears most frequently at the axilla. Benign and malignant processes in general breast tissue can occur in accessory breast tissue. We report a case of 76-year-old female presented with palpable, huge mass at the right axilla which pathology of the mass was borderline phyllodes tumor. Phyllodes tumors arising in accessory breast tissue is an extremely rare condition. And this case study showed more detail on phyllodes tumor which would encourage the advance in management of the disease.