PER1 and breast cancer: The main objective of our project was to investigate an association between genetic variants of crucial circadian genes CLOCK, NPAS2, BMAL1, PER1, 2, 3, CRY1, 2, and TIMELESS and the risk of BC, progression, and the influence of gene expression on BC tissue pairs to demonstrate their functional significance in the process of carcinogenesis in the mammary gland.