Background: Sufficient sleep and maintenance of circadian rhythm are important to health. We have shown that short duration of sleep before diagnosis is associated with higher-grade tumors among breast cancer patients. Earlier studies suggest that genetic variation in the CLOCK gene is associated with risk of cancers, including breast cancer. Studies of the association of genetic variation, including in CLOCK, and tumor grade, a standard marker of tumor aggressiveness, are lacking.
Methods: We investigated the relationship between single nucleotide polymorphisms (SNPs) in the CLOCK gene and tumor grade and estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 status in 293 breast cancer patients. Nine SNPs were determined by standard TaqMan assays. Tumor grade, receptor status, and other clinical variables were abstracted from medical records.
Results: Two SNPs were excluded because of poor genotyping performance. None of the remaining seven variants had a statistically significant association with breast cancer tumor grade or with receptor status.
Conclusion: As with all novel studies, further work is needed to examine the association of CLOCK and other genes in the circadian rhythm pathway with breast cancer tumor grade in other populations.