Women who sleep less are more prone to breast cancer recurrence, according to the first study to show such an association. The findings suggest, according to the Case Western Reserve researchers, that lack of sleep contributes to biologically more aggressive tumors.
After adjusting for age, body mass index, physical activity, and smoking, investigators in Cleveland, Ohio, found an inverse correlation between average hours of sleep per night before cancer diagnosis and cancer recurrence in women with estrogen-receptor-positive (ER+) stage I-III breast cancer. To gauge recurrence, the researchers used OncotypeDX scores. (OncotypeDX is a widely used test to guide treatment and predict likelihood of recurrence in early-stage ER+ breast cancer.)
Women in the study who slept ≤ 6 hours per night before diagnosis had higher average OncotypeDX scores than those who slept a minimum of 7 hours per night. (The higher the score, the higher the risk of recurrence.) When the researchers limited the population to postmenopausal women, risk of recurrence was more than twice as high in women who averaged ≤ 6 hours of sleep per night compared with those who slept at least 7 hours per night.
Published in Breast Cancer Research and Treatment, the study reviewed medical records of 412 women diagnosed with ER+ breast cancer since 2007 (when OncotypeDX testing became available). The report suggests that increased estrogen and altered ER activity in response to reduced melatonin from a sleep deficit may contribute to the association.
The researchers commented that their study’s weaknesses included its reliance on self-report, retrospective design, almost purely Caucasian population, and its modest sample size. They concluded, however, that women who sleep less than 7 hours per night and develop breast cancer may develop more aggressive disease, and that additional research about circadian rhythm patterns and breast cancer aggressiveness is needed.
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