Abstract P3-12-33: Breast cancer incidence rates in Japan showed unimodal age distribution

Abstract

Abstract Purpose: Breast cancer incidence rates in Japan have been increasing recently. The incidence rates show bimodal age distribution in the developed countries. The latest studies have thrown new light on a close association between etiologic subtypes and the bimodal age distribution. To determine whether bimodal age distributions are also present in Japanese breast cancer, we investigated Japanese breast cancer incidence rates by age and biological features involved in incidence rates.Methods: Using Japanese breast Cancer Registry data, we examined age-at-diagnosis frequency distributions of breast cancer for 2017 and their hormone receptors (estrogen and progesterone) and HER2 status. Japanese female population data were referred to the registry of Statistics Bureau of Japan. Results: We included 94,612 breast cancer cases for 2017 in Japan. The number of breast cancer cases showed bimodal age distributions at 45-49 years and 65-69 years. However, the age distributions altered to unimodal age distribution with slight peaked at 45-49 years by adjusting with Japanese female population. Estrogen and progesterone receptor rates showed higher level at 45-49 years than other age groups (92.3% and 86.8%, respectively). HER2 expression rates showed lower rates (12.2%) at 45-49 years than other age groups.Conclusions: Japanese breast cancer incidence rates showed unimodal age distribution with slight peaks at 45-49 years. Luminal type breast cancer accounted for younger ages at 45-49 than elderly. Etiology of Japanese female breast cancer was different from the developed countries represented as bimodal age distribution. Citation Format: Ken Uchida, Hitoshi Ohashi, Hiroko Nogi. Breast cancer incidence rates in Japan showed unimodal age distribution [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-33.