A case of postmenopausal breast cancer becoming HER2 positive after neoadjuvant hormone therapy

: A 75-year-old woman presented to a local doctor with a lump in the right breast. On physical examination, a tumor measuring 24mm was palpable in the BD area of her right breast. Mammography showed category 5 disease, and ultrasonography revealed a tumor measuring 24×16 mm. A mammotome biopsy provided a diagnosis of invasive ductal carcinoma of the breast(ER 7/PgR 4/HER2 1+), and the tumor was classified as stage IIA(T2N0M0)according to the UICC-TNM classification. She was recommended surgery but she rejected this option and underwent hormone therapy with anastrozole (1mg/day). One year and 8months after beginning the treatment, ultrasonography showed the tumor to measure 7.0×5.7 mm, and hormone therapy resulted in a partial response(PR). The patient hoped to undergo an operation, so she was referred to our hospital, and a right partial mastectomy and sentinel node biopsy was performed. A histopathological exami- nation indicated scirrhous carcinoma, 18mm, nuclear grade 1, f, ly1, v0, n0, ER 3/PgR 3/HER2 3+. The curative effect was grade 1a. The tumor had become HER2 positive, so the patient was then administered radiotherapy and trastuzumab and anastrozole as adjuvant therapy. Herein, we report our experience with a case of breast cancer that only became HER2 positive after hormone therapy, and also provide some bibliographic comments on this occurrence.