Abstract
PURPOSE: Circadian rhythms control a wide range of physiological processes and may be associated with fatigue, depression, and sleep problems. We aimed to identify subgroups of breast cancer survivors based on symptoms of fatigue, insomnia, and depression; and assess whether circadian parameters (i.e., chronotype, amplitude, and stability) were associated with these subgroups over time. METHODS: Among breast cancer survivors, usual circadian parameters were assessed at 3-4 months after diagnosis (T0), and symptoms of fatigue, depression, and insomnia were assessed after 2-3 years (T1, N = 265) and 6-8 years (T2, N = 169). We applied latent class analysis to classify survivors in unobserved groups ("classes") based on symptoms at T1. The impact of each of the circadian parameters on class allocation was assessed using multinomial logistic regression analysis, and changes in class allocation from T1 to T2 using latent transition models. RESULTS: We identified 3 latent classes of symptom burden: low (38%), moderate (41%), and high (21%). Survivors with a late chronotype ("evening types") or low circadian amplitude ("languid types") were more likely to have moderate or high symptom burden compared to "morning types" and "vigorous types," respectively. The majority of survivors with moderate (59%) or high (64%) symptom burden at T1 had persistent symptom burden at T2. IMPLICATIONS FOR CANCER SURVIVORS: A late chronotype and lower circadian amplitude after breast cancer diagnosis were associated with greater symptoms of fatigue, depression, and insomnia at follow-up. These circadian parameters may potentially be novel targets in interventions aimed at alleviating symptom burden among breast cancer survivors.