A 50-year-old woman aware a lump in the right axillary area 5 years ago.She noticed that the lump gradually became bigger, accompanied by redness and gathering of the skin; therefore, she consulted a dermatologist.On receiving the result of skin biopsy, she was referred for a suspected metastatic lesion from breast cancer.The mass was 20mm in diameter, was palpable in the right axillary area, and accompanied by redness of the skin.Ultrasonography revealed 2 irregular-shaped masses in the right axillary area.An FDG/PET study showed some abnormal uptake in the right axillary area, but there were no other primary lesions in any other organs.We performed tumorectomy, and the axillary tumors was histopathologically diagnosed as invasive ductal carcinoma.This case was comprehensively presumed to be accessory breast cancer.In the case of malignant tumor in the axillary area, differential diagnoses are axillary lymph node metastasis of latent breast cancer, ectopic breast cancer, accessory breast cancer, and malignant tumors of skin and its appendages.We presented here a case of carcinoma that was estimated as accessory breast cancer considering clinical, radiological and pathological findings in an integrating manner.