Self-reported cognitive decline in Japanese patients with breast cancer treated with endocrine therapy

Background Despite contributing to the control of hormone receptor-positive breast cancer, a highly prevalent cancer type, endocrine therapy affects patients' cognitive function. We aimed to identify cognitive decline following the start of endocrine therapy using patient-reported measures and investigate factors associated with cognitive difficulties. Methods This cross-sectional survey used a self-administered, anonymous questionnaire. The participants were 876 patients with breast cancer who experienced subjective cognitive difficulties after starting endocrine therapy. Our sample was recruited from 11 patient advocacy groups, 5 clinics, and 2 hospitals in Japan. The questionnaire assessed subjective cognitive difficulties (30 items), psychological well-being, demographic and clinical information, and other subjective symptoms. Results Of 510 (58.2%) responses, we analyzed 405 (46.2%) questionnaires. Exploratory factor analysis identified three factors of cognitive difficulties: Factor 1, "difficulties in manipulating memory and language;" Factor 2, "difficulties in processing multiple pieces of information;" and Factor 3, "difficulties in maintaining attention and concentration." Factor 1 was the most common type, and it was significantly related to the treatment characteristics of endocrine therapy. Multivariate logistic regression analysis revealed that fewer household members, a history of breast surgery, more severe menopausal symptoms, and greater psychological distress were significantly associated with cognitive difficulties. As cognitive difficulties increased, the proportion of participants suspected to have psychological disorders increased significantly. Conclusions Patients treated with endocrine therapy for breast cancer experience intricately intertwined impairments in several domains of cognitive function. They have an increased risk of psychological disorders corresponding to the degree of subjective cognitive function.