Panorama of diseases associated with breast cancer

Breast cancer is the most common cancer in women. Although the incidence of breast cancer has increased over time, so too has patient survival. Given these trends, the prevalence of breast cancer has steadily increased in recent decades, exposing these women to other associated diseases which can influence carcinogenesis, prognosis, and treatment. This thesis uses Swedish register data, combined with data from the Libro-1 and Karolinska Mammography Project for Risk Prediction of Breast Cancer (KARMA) cohorts, to study other diseases associated with breast cancer in women. Specifically, this thesis investigates how diseases in early adulthood influence the risk of breast cancer, and how overall health is affected by breast cancer treatment. In Study I, the risk of breast cancer in women with and without preeclampsia was studied using data from the Swedish Medical Birth Register and KARMA cohort. Women diagnosed with preeclampsia had a decreased risk of breast cancer and lower mammographic density. In addition, sisters of breast cancer patients and women with a high genetic predisposition to breast cancer had a lower risk of preeclampsia. This suggests that inherited factors may contribute to the inverse association between preeclampsia and breast cancer. In Study II and Study III, the risk of mental disorders and psoriasis were compared between a Swedish nationwide cohort of breast cancer patients and the general population. Women with invasive breast cancer had an increased risk of depression, anxiety, stress-related disorders, and psoriasis. This increased risk was greatest shortly after cancer diagnosis and remained over the subsequent five years. Patients with in-situ breast cancer only experienced an increased risk of stress-related disorders during the first six months after cancer diagnosis. With regard to risk predictors, the Libro-1 cohort of Stockholm-Gotland breast cancer patients showed that younger age at diagnosis, higher tumor grade, lymph node positive tumors, comorbidity, and chemotherapy were ...