Age‐specific breast cancer incidence by subtype, <scp>TNM</scp> 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.