Insomnia in breast cancer: Independent symptom or symptom cluster?

OBJECTIVE: This study examined insomnia in the context of breast cancer, both as an independent symptom and as a component of a symptom cluster that includes depression, anxiety, fatigue, and pain.

METHOD: Women with a history of breast cancer currently taking an aromatase inhibitor and who had completed cancer treatment at least one month prior to enrollment were included (n = 413). Participants completed validated measures of insomnia, fatigue, pain, depression, and anxiety. Factor analysis was utilized to examine the extent to which these symptoms could be represented by common latent factors. Insomnia severity was then separated into a symptom cluster component (I-SC) and an insomnia-unique (I-U) component. The associations between each insomnia component and demographic and clinical factors were examined in multivariate models.

RESULTS: A single-factor solution provided the best fit to the symptom measures. Some 53.3% of the variance in insomnia severity was captured by this symptom cluster (I-SC), with the remaining 43.7% being unique to insomnia (I-U). Unique patterns of demographic factors (e.g., age and body-mass index), but not clinical factors, were associated with each insomnia measure.

SIGNIFICANCE OF RESULTS: Approximately 50% of insomnia severity was related to the symptom cluster, with the rest being unique to insomnia. Different sociodemographic risk factors were related to the different insomnia measures. Stronger underlying foundations for the mechanisms of each component could lead to refined diagnoses and targeted interventions for addressing the overall insomnia burden in cancer patients.