Annual report of national clinical database-breast cancer registry in 2023: systemic therapy for small breast cancer.

This annual report of the National Clinical Database-Breast Cancer Registry (NCD-BCR) by the Japanese Breast Cancer Society presents nationwide breast cancer statistics for patients registered in Japan in 2023. Among 107,372 patients with breast cancer at 1317 institutions, 99.3% were females with a median age of 62 years. The distribution of the clinical stages was as follows: stage 0 (15.5%); stage I (42.1%); stage II (31.1%); stage III (7.0%); and stage IV (2.1%). Estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) positivity was observed in 78.9%, 70.0%, and 13.3% of patients, respectively. Among 102,717 patients without distant metastases, 41.2% underwent breast-conserving surgery, 76.5% underwent sentinel lymph node biopsy, and 6.0% underwent breast reconstruction. The distribution of radiotherapy was as follows: 75.2% received whole-breast irradiation, 15.7% chest-wall irradiation, and 20.7% regional irradiation. Among the 13,061 patients with pT1abN0M0 breast cancer, comprising 10,819 hormone receptor [HR]-positive/HER2-negative, 1479 HER2-positive and 763 HR-negative/HER2-negative individuals, 92.4% of HR-positive/HER2-negative patients received endocrine therapy, 46.9% of HER2-positive patients received chemotherapy and/or anti-HER2 therapy, and 31.2% of HR-negative/HER2-negative patients received chemotherapy. This annual report provides a nationwide overview of contemporary systemic therapy patterns in small breast cancer and highlights size‑dependent and subtype‑specific use of systemic therapy in Japan, reflecting a risk‑adapted treatment strategy.