[Two Cases of ER-Positive Postmenopausal Breast Cancer That Increased in Size during Neoadjuvant Hormone Therapy].

Abstract The first patient was a 62-year-old woman who was referred to our hospital with the complaint of a left breast tumor. She was diagnosed with invasive ductal carcinoma(T1N0M0, stage I). The tumor was ER-positive, PgR-negative, and HER2- negative. She was treated with toremifene, letrozole, and anastrozole as neoadjuvant hormone therapy for 4 months, but the tumor increased in size. The clinical response was judged as progressive disease, and a left partial mastectomy and axillary lymph node dissection were performed. Chemotherapy and radiotherapy were performed after surgery. The second patient was a 68-year-old woman who was referred to our hospital with the complaint of a right breast tumor. She was diagnosed as invasive ductal carcinoma(T1N0M0, stage I). The tumor was ER-positive, PgR-negative, and HER2-negative. She was treated with letrozole as neoadjuvant hormone therapy for 4 months, but the tumor increased in size. The clinical response was judged as progressive disease, and a right partial mastectomy and axillary lymph node dissection were performed. Chemotherapy and radiotherapy were performed after surgery. Although the evidence is still insufficient, with neoadjuvant hormone therapy for hormone-sensitive breast cancer, improved tumor shrinkage and breast conservation have been reported. We experienced two cases in which the tumor increased in size during neoadjuvant hormone therapy; however, even though these cases showed no apparent effect, chemotherapy may be effective in future cases.