Changing socioeconomic patterns of breast cancer incidence, mortality and survival in Norway

Abstract

Breast cancer has had a reversed socioeconomic gradient compared to most diseases. For decades, women with a high socioeconomic status have had the highest risk of being diagnosed with breast cancer and dying from breast cancer. However, since the new millennium, socioeconomic patterns for breast cancer incidence and mortality seem to be changing. To better understand these changing patterns, this thesis aimed to describe socioeconomic differences over time in breast cancer incidence, mortality and survival in Norway. Three epidemiological studies were performed using individually-linked Norwegian registry data covering the entire female population of Norway. Breast cancer incidence and mortality trends were analysed with Poisson models, whereas breast cancer survival trends were analysed with flexible parametric models. These analyses revealed a changing socioeconomic pattern for breast cancer in Norway favouring women with a high socioeconomic status. Women with high socioeconomic status have had a more modest increase in breast cancer incidence, and greater decline in breast cancer mortality over time, compared to women with low socioeconomic status, in particular for young women below age 50 years. Since the new millennium, young women with a low socioeconomic status are still less often diagnosed with breast cancer but now die more often from breast cancer than young women with a high socioeconomic status. Late detection does not seem to play a role, but other factors relating to prognosis after diagnosis seem to explain the higher breast cancer mortality for young women with low socioeconomic status. Even in a country with universal health care, socioeconomic factors such as education and income level seem to play a role for breast cancer outcomes.