Trends in the clinical stage distribution of breast cancer in Osaka, Japan

We examined the proportion of screen-detected breast cancer cases and clinical stage distribution by age group among female breast cancer cases in Osaka, Japan using population-based cancer registry from the period 1980 to 2012. The proportion of local cases increased and that of regional cases decreased gradually during the study period. The proportion of distant cases leveled off. The proportion of in situ cases increased rapidly after 2003. This increase was noticeable for women aged 30–39, 40–49, 50–59, and 60–69 years. The proportion of in situ cases for women aged 40–49, 50–59, and 60–69 years reached 15.4, 11.3, and 9.9% in 2010–2012, respectively. Regarding screening status, the proportion of screen-detected cases before 1988 was under 3%. Between 1989 and 2003, it leveled off at around 5%. After 2003, the proportion increased noticeably, and reached 25.4%:34.0% in aged 40–49 years, 32.8% in aged 50–59 years, and 26.7% in aged 60–69 years. The increase in local cases and decrease in regional cases would be due to awareness of breast cancer, probably a result of developments in medical diagnostic technology. On the other hand, the steep increase of in situ cases might be due to screening. We need careful monitoring of the trends in breast cancer incidence by clinical stage.