Trends and Age-Period-Cohort Effect on Incidence of Male Breast Cancer from 1980 to 2019 in Taiwan and the USA

Simple Summary Although male breast cancer (MBC) is globally rare, its incidence significantly increased from 1990 to 2017. The aim of this study was to examine variations in the trends of MBC incidence between populations in Taiwan and the USA. Analysis of related databases from the two countries showed MBC incidence in Taiwan rapidly increased in contrast to the much slower increase in the USA during the same period. Furthermore, the results of the age-period-cohort analysis demonstrated a stronger cohort effect on the MBC incidence trend in Taiwan than in the USA. The observed cohort effect in this study is similar to that of a prior investigation on female breast cancer in Taiwan, indicating the potential influence of common environmental factors in both genders, such as a high-fat diet and xenoestrogen.Abstract Although male breast cancer (MBC) is globally rare, its incidence significantly increased from 1990 to 2017. The aim of this study was to examine variations in the trends of MBC incidence between populations in Taiwan and the USA from 1980 to 2019. The Taiwan Cancer Registry database and the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute of the USA were used. The age-standardized incidence rate was calculated using the world standard population in 2000. The long-term trends of the age, time period, and birth cohort effect on MBC incidence rates were estimated using the SEER Age-Period-Cohort Web Tool. The results revealed that the incidence of MBC in both countries increased from 2010 to 2019 (Taiwan: average annual percentage change (AAPC) = 2.59%; USA: AAPC = 0.64%). The age and period effects on the incidence rates in both countries strengthened, but the cohort effect was only identified in Taiwan (Rate ratio: 4.03). The identified cohort effect in this study bears resemblance to that noted in a previous investigation on female breast cancer in Taiwan. This suggests the possible presence of common environmental factors influencing breast cancer incidence in both genders, such as a high fat diet and xenoestrogen.