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

To examine age-specific breast cancer incidence trends.

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.

The most recent breast cancer age-specific trends were observed to be increasing for all age groups under age 55, especially 45-49 since 2018 (APC = 2.4, P < .001); were stable for 55-59, and decreasing for age groups within 60-74, though not significantly for 70-74 (APC = -0.4, P = .076). 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).

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.