Updated Breast Cancer Incidence in Canadian Women by Age: Divergent Trends

PURPOSE: To examine age-specific breast cancer incidence trends. METHODS: Breast cancer case counts were obtained from the National Cancer Incidence Reporting System (1984-1991) and the Canadian Cancer Registry (1992-2023) both housed at Statistics Canada. Trends in age-specific and age standardized incidence rates (ASIR), and associated annual percent changes (APC), were determined using JoinPoint. An increasing breast cancer ASIR trend was observed throughout the study period except for 1999-2004. Between 1984-1986 and 2021-2023 incidence rates increased in each age group <85; however, they decreased among women 90+ by 23.5%. Apart from the 55-59 age group, relative increases of 20% or more combined with absolute increases of 50 per 100 000 or more between these two periods were observed for each age group between 50-54 and 70-74. The largest absolute increase occurred among women 65-69 (76.1 per 100 000). The age group corresponding to the peak incidence rate has become younger over time from 90+ (1984-1986) to 70-74 (since 2011-2013). CONCLUSION: Highlighted by increasing rates among younger women, especially those 45-49, recent trends in age-specific breast cancer incidence rates are diverging with important implications for screening and clinical care. Over several decades, the shape of the age-specific breast cancer incidence rate curve has changed with peak incidence occurring at a younger age.