Annual report of National Clinical Database-Breast Cancer Registry in 2021: characteristics categorized by body mass index and menopause status.

The Japanese Breast Cancer Society initiated the breast cancer registry in 1975 and migrated the registry to the National Clinical Database-Breast Cancer Registry (NCD-BCR) in 2012. This annual report presents 2021 data on the NCD-BCR. We analyzed data from 98,540 breast cancer (BC) cases registered in 2021. In 2021, 99.4% of BC cases were females with a median age of 61. Most (57.5%) were diagnosed at early stages (Stage 0 or I). Breast-conserving surgery was performed in 42.8% of cases. Sentinel lymph node biopsy was performed in 67.8%, followed by radiotherapy in 71.0% of those post-conserving surgery. Regarding postoperative systemic therapy, 63.1% received endocrine therapy, 28.2% received chemotherapy, and 14.9% received molecular-targeted therapy. ER positivity was observed in 75.2%, HER2 in 13.6%, and Ki67 ≥30% in 29.1% of cases. The median age of premenopausal cases was 46 (interquartile range, 42-49) years and the median BMI was 21.5 (19.7-24.2) kg/m² whereas the median age of postmenopausal cases was 69 (61-76) years and the median BMI was 23.0 (20.6-25.9) kg/m². In premenopausal cases, cases with normal BMI were more likely to be found at checkups without subjective symptoms and in the early stage than those with high BMI. The tendency of ER, PgR, HER2, and Ki67 status on BMI differed by menopause status; premenopausal cases with a lower BMI showed higher proportions of ER- and PgR-positive cancer and lower proportions of cancer with high Ki67. These nationwide descriptive statistics would help clinical explanation and further research on breast cancer.