Age-specific breast cancer incidence by subtype, TNM stage and screening status in Sweden 2008-2019 estimated with multiple imputation.

Breast cancer incidence in women increases with age, but less is known about which subtypes contribute the most at different ages. We describe age-specific breast cancer incidence rates in Sweden by subtype, TNM stage and screening status. Population-based data were retrieved from the Swedish National Quality Register for Breast Cancer on 89,322 invasive breast cancer cases diagnosed 2008-2019 in women ≥18 years. Breast cancer subtypes were defined by estrogen and progesterone receptors, human epidermal growth factor receptor 2 (HER2), and grade. Poisson regression with multiple imputation estimated proportions and incidence rates. In women <40 years, the breast cancer incidence rates were low with luminal HER2, HER2 positive and triple-negative breast cancer (TNBC) accounting for 57% of tumors. During screening ages (40-74 years), luminal A-like tumors accounted for 59% and their incidence rate increased by age. Luminal A-like tumors were more often screen-detected (70%) compared to HER2 positive (45%) and TNBC (42%). At age 75 years, the incidence rates declined temporarily for all subtypes, and remained mostly stable in older ages, although the luminal A-like rates did not reach the same levels as 40-74 years. In the screening ages, stage I incidence rates were increased, especially for the luminal A-like subtype, while in post-screening ages (≥75 years), stage II incidence rates were highest, especially for luminal B-like, luminal HER2 and TNBC subtypes. Age-specific incidence patterns vary by subtype and are all influenced by screening. Future diagnostic and preventive interventions should consider these age-specific patterns.