Abstract P4-03-08: Breast cancer incidence rates in Japan turned into bimodal age distribution in this decade

Abstract

Abstract BACKGROUND: Japan is the globe’s fastest ageing country: 32.0 % of the female population are 65 or older in 2021. The birth rate was 1.30 children per woman in 2021. Japan’s population has been constantly shrinking since 2011 with aging. The number of breast cancer cases has increased rapidly in the course of low birth rate and aging population. Breast cancer has increased and accounted for the first place of all of cancers in Japanese women. OBJECTIVES; Number of breast cancer has increased recently and accounted for the first place of all of female cancers in Japan. Detailed analytics of the increase and aging of breast cancer are not studied. We elucidate the transformation of Japanese breast cancer by ages at diagnosis over the past decade. MATERIALS: We used the registry data of Japanese Breast Cancer Society and Statistics Bureau of Japan in 2018. Female breast cancer new cases were 59,389 patients in 2008 and 93,858 patients in 2018, respectively. The total female population was 65.441 million in 2008 and 64.911 million in 2018, respectively. 65 years and older women accounted for 23.4% in 2008 and 31.0 % in 2018, respectively. METHODS: We compared incidences and incidence rates of breast cancer by ages in 2008 and 2018, respectively. We used the statistical method of Ameijeiras-Alonso et al for mode assessment. RESULTS; Total number of incidences and incidence rates of breast cancer in 2018 were higher than those in 2008 among all ages. Difference of number of incidences were maximum in age of 60-69 in both years. Difference of incidence rates in both years reached maximum in age of 75-79. Incidence rates in 2008 showed unimodal age distribution with the gentle peak. Incidence rates in 2018 showed bimodal age distribution with two peaks of 45-49 and 65-69. CONCLUSIONS; Incidences and incidence rates of breast cancer increased rapidly among all ages in this decade in Japan. The incidence rates increased most in ages of 75-79 and turned into bimodal age distribution in 2018. Citation Format: Ken Uchida, Hitoshi Ohashi, Hiroko Nogi, Satoki Kinoshita, Ryouko Nosaka, Makiko Kamio. Breast cancer incidence rates in Japan turned into bimodal age distribution in this decade. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-03-08.