Associations between multimorbidity and depression among breast cancer survivors within the UK Biobank cohort: a cross-sectional study.

Background: Advances in the early detection of cancer and its treatment have resulted in an increasing number of people living with and beyond breast cancer. Multimorbidity is also becoming more common in this population as more people live longer with breast cancer and experience late effects of cancer treatment. Breast cancer survivors have heightened risk of depression, but to what extent multimorbidity affects the mental health of this population is less clear. This study aims to investigate the association between multimorbidity and depression among women living with and beyond breast cancer in the UK Biobank cohort.

Methods: Data from UK Biobank (recruitment during 2006 to 2010, aged 40-70 years) were used to identify 8438 women with a previous diagnosis of breast cancer via linked cancer registries in England, Scotland and Wales. The lifetime number of chronic conditions was self-reported and multimorbidity defined as 0, 1, 2, 3, 4 or 5+. The Patient Health Questionnaire (PHQ-2) was used to define participants that were likely to have depression based on their symptom reporting at baseline. Logistic regression models were used to analyse the associations between multimorbidity and depression, accounting for a number of potential sociodemographic confounding variables (including age, ethnicity, socioeconomic deprivation, education level and marital status) and characteristics related to the cancer (number of years since diagnosis and recurrence/secondary cancer).

Results: Multimorbidity was common among breast cancer survivors, with 32.9% of women experiencing one and 30.1% experiencing two or more chronic health conditions. Hypertension (25.8%), painful conditions (18.3%), and asthma (11.6%) were the three most common co-morbid conditions. 5.3% of participants had current depression. A strong, dose-response relationship was found between multimorbidity and the likelihood of depression (OR = 2.09, 95% CI: 1.56-2.79 for two conditions and OR = 6.06, 95% CI: 3.63-10.14 for five or more conditions).

Conclusions: Multimorbidity and depression were strongly associated among female UK Biobank participants with a previous breast cancer diagnosis. This association became increasingly pronounced as the number of chronic comorbid conditions increased. As more people survive cancer for longer, increasing recognition and support for multimorbidity and its impact on mental health is needed.