Sleep and breast cancer in the western New York exposures and breast cancer (WEB) study

Study Objectives: Night shift work is associated with increased breast cancer risk, possibly from altered sleep. Epidemiologic evidence is sparse regarding sleep disturbances and breast cancer tumor markers. We examined sleep disturbance in association with breast tumor aggressiveness and mortality following diagnosis. Methods: We analyzed associations of measures of sleep disturbance in a sample of 1, 122 incident breast cancer cases from the Western New York Exposures and Breast Cancer (WEB) Study. Sleep disturbance was assessed using self-administered questionnaires; responses about difficulty falling asleep, waking up frequently, having trouble staying asleep, and waking up feeling tired and worn out were used to create a summary sleep disturbance score. We used general linear models to examine associations of sleep disturbance with markers of tumor aggressiveness among cases: estrogen receptor (ER) status, progesterone receptor (PR) status, and human epidermal growth factor receptor-2 (HER2) status; tumor size, stage, grade, lymph node involvement, and presence of metastasis. In addition, we examined the association between sleep disturbance and survival using Cox regression. Results: Among breast cancer cases, sleep disturbance was higher for women with ER-/ PR-tumors compared to women with ER+ / PR+ tumors, even after adjusting for potential covariates (P for trend = .02). Results suggest that the association of sleep quality differs by menopausal status, where mild sleep disturbance is associated with higher breast cancer mortality in premenopausal women; however, we had a relatively small sample size. Conclusions: Sleep disturbance may be associated with aggressive subtypes of breast cancer; however, further studies are needed.