Sleep Quality, Duration and Breast Cancer Tumor Aggressiveness
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Background: Epidemiological studies have reported that poor sleep quality and short sleep duration may increase breast cancer risk. However, whether sleep is associated with breast cancer tumor aggressiveness, particularly in regard to hormone receptor status, tumor stage, and tumor grade has been largely unexplored. Study Design: Using data from the Women's Health Initiative (WHI) Observational Study, we prospectively studied 4,603 postmenopausal women (non-Hispanic whites [n=4171], African Americans [n=235], Hispanic/Latina [n=98], and Asian/Pacific Islanders [n=99]) who developed incident, primary, and histologically-confirmed invasive breast cancer (average years of follow up = 6.9). We hypothesized that poor sleep quality and short sleep duration are associated with aggressive breast tumor types. Methods: Assessment of sleep quality and duration were measured from questionnaires self-administered at WHI baseline (1993-1998). The validated WHI Insomnia Rating Scale (WHIIRS) assessed one form of sleep quality: sleep disturbance. The following tumor markers were available in breast cancer cases to assess tumor aggressiveness: tumor grade, tumor stage, estrogen receptor status (ER), progesterone receptor status (PR), and triple negative status (ER, PR and HER2-negative). Logistic regression was used to estimate odds ratios (ORs) and 95% Confidence Intervals (CIs) for having aggressive breast cancer tumor markers. OR and 95% CIs were adjusted for age, body mass index, hormone therapy use, income, smoking status, pack years, alcohol intake, and physical activity. Because of the difference in distribution of both sleep and breast cancer tumor types between race/ethnic groups, we examined these groups separately. Results: Among African Americans, those who reported 'very sound or restful', or 'sound or restful' typical night's sleep we observed 66% lower odds of triple negative tumors (vs. non-triple negative) compared to those who reported average quality sleep: OR: 0.34, 95% CI: 0.13-0.90. We found a significant inverse association between continuous sleep duration and the stage of breast cancer tumors for non-Hispanic whites (OR: 0.92, 95% CI: 0.85-0.99). Conclusion: Our study found further indication that poor sleep quality, and short sleep duration are associated with more aggressive tumors. This was the largest study to date to examine prospectively sleep and breast cancer aggressiveness with validated sleep measures and long-term follow-up. Since sleep quality and duration were found to be associated with breast cancer tumor aggressiveness, lifestyle recommendations should be made, as sleep is a potentially modifiable factor.