The longitudinal relationship between fatigue and sleep in breast cancer patients undergoing chemotherapy

Fatigue and sleep disturbances are two of the most common and distressing symptoms of cancer patients. A relationship between the two symptoms was reported in symptom cluster studies; however, only subjective measurements of sleep were examined and most studies were cross-sectional. In this study of women with breast cancer undergoing chemotherapy, we explored the longitudinal relationship between fatigue and sleep measured both subjectively and objectively.

Prospective study. Data were collected at 7 time points: before (baseline) and during the 3 weeks of cycle 1 and cycle 4 chemotherapy.

Ninety-seven women with newly diagnosed stage I-III breast cancer who were scheduled to receive at least four 3-week cycles of chemotherapy.

Objective sleep parameters were measured with an Actillume actigraph (Ambulatory Monitoring Inc.). Subjective sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). Fatigue was assessed with the Multidimensional Fatigue Symptom Inventory-Short Form (MFSI-SF). Fatigue became worse during both cycles of chemotherapy (P-values < 0.01). Subjective sleep quality was poor at baseline and remained unchanged throughout treatment. Objective nighttime and daytime total sleep time increased compared to baseline during the treatment administration week of both cycles; daytime total wake time decreased during the treatment week of both cycles and during the last 2 week of cycle 4. Mixed model results revealed that fatigue was positively associated with total PSQI scores and with objective measures of total nap time, and negatively associated with total wake time during the day (all P-values < 0.01).

Fatigue was significantly associated with subjective reports of poor sleep and objective measures of daytime sleepiness, but not with nocturnal sleep as measured with actigraphy. This relationship between fatigue and sleep warrants further studies to explore their possible common underlying etiology.