A 42-year-old female visited our hospital because of left breast tumor and left arm swelling with severe pain. She had had right radical mastectomy and bilateral oophorectomy at 27 and 29 years of age, respectively. On admission, she had a hard mass, which seemed to be a severe invasion of the chest wall, on her left breast with a severe nipple ulcer. We inserted a catheter operatively through the thyrocervical truncus to the subclavian artery for the arterial infusion therapy. She was administered 250 mg of 5-FU daily, and 10 mg of ADM, 10 mg of CDDP, 10 KE of OK-432, every other week. During 70 days, 10,000 mg of 5-FU, 50 mg of ADM, 50 mg of CDDP and 50 KE of OK-432 were administered. As soon as the breast tumor became smaller, showed some mobility and the nipple ulcer healed, we carried out left mastectomy and axillary lymph node dissection. Pathological findings showed severe degeneration and necrosis of cancer cells. Lymphocytes surrounded necrotic tissue, and there was a follicular pattern of invasion. This phenomenon was considered to result from the promotion of cellular immunological reaction by OK-432.