Excess mortality from breast cancer in female breast cancer patients with severe mental illness.

Women with a history of severe mental illness (SMI) have elevated breast cancer mortality. Few studies have compared cancer-specific mortality in women with breast cancer with or without SMI to reveal gaps in breast cancer treatment outcomes. We compared breast-cancer specific mortality in women with or without SMI and investigated effects of stage at presentation, comorbidity, and differences in cancer treatment. Women with their first breast cancer diagnosis in 1990-2013 (n = 80,671) were identified from the Finnish Cancer Registry, their preceding hospital admissions due to SMI (n = 4,837) from the Hospital Discharge Register and deaths from the Causes of Death Statistics. Competing risk models were used in statistical analysis. When controlling for age, year of cancer diagnosis, and comorbidity, breast cancer mortality was significantly elevated in patients with SMI. Relative mortality was highest in breast cancer patients with non-affective psychosis, partly explained by stage at presentation. Mortality was also significantly elevated in breast cancer patients with a substance use disorder and mood disorder. Patients with SMI received radiotherapy significantly less often than patients without SMI. Our findings emphasize the need to improve early detection of breast cancer in women with SMI and the collaboration between mental health care and oncological teams.