[Decision-Making Regarding Adjuvant Therapy for Hormone Receptor-Positive, HER2-Negative Early Breast Cancer]

In December 2021, abemaciclib was approved as an adjuvant treatment for hormone receptor-positive, HER2-negative, high-risk early breast cancer in Japan. The Oncotype DX Breast Cancer Recurrence Score program(Oncotype DX)is a test that can be used to limit overtreatment in hormone receptor-positive, HER2-negative, low-risk early breast cancer. Although the target groups of both these are different and usually without many overlapping indications, we encountered a case in which this therapy and test were used in a short time period. Our experience suggests that even if the result of Oncotype DX indicates that hormone therapy alone is sufficient, it does not imply that abemaciclib is unnecessary, although this has not been directly studied in the monarchE trial. While a wider choice of treatment options is desirable for patients, more clinical data and trials are needed to further validate the utility of abemaciclib without chemotherapy.