[Early Breast Cancer Treated with Adjuvant S-1 plus Endocrine Therapy-A Report of Two Cases]

We report 2 cases of early breast cancer treated with adjuvant S-1 plus endocrine therapy. In case 1, a 70-year-old woman was diagnosed with right breast cancer and underwent partial mastectomy. The histopathological diagnosis was invasive ductal carcinoma(solid type), positive for estrogen receptor(ER)and progesterone receptor(PgR), negative for HER2/neu. The Ki-67 labeling index was 14%. The diameter of invasion was 27 mm, no lymph node metastasis was observed, and we confirmed the diagnosis as pT2N0M0, Stage ⅡA. A venous invasion was observed and the histological grade was Ⅱ. In case 2, a 53-year-old woman was diagnosed with left breast cancer and underwent lumpectomy. The histopathological findings showed a solid-tubular carcinoma, characterized by ER-positive, PgR-positive, HER2-negative. The Ki-67 labeling index was 24%. The tumor had an invasion of 20 mm and was diagnosed as Stage Ⅰ early-stage cancer, but there were some venous invasions and the histological grade was Ⅲ. We judged that both patients were at intermediate risk of recurrence and administered S-1 in addition to endocrine therapy. Even in cases without axillary lymph node metastasis, this combination of S-1 with endocrine therapy was considered to be a useful treatment option if the criteria of the POTENT trial were met.