PER2 and neoplasm: In order to determine whether circadian genes expression, including CLOCK, NPAS2, BMAL, CRY1, CRY2, PER1, PER2, PER3, TIMELESS, and CSNK1E, was altered in the breast tumor samples, we performed quantitative Real-Time PCR with intercalating SYBR Green in the 107 pairs of the tumor tissue and non-tumor adjacent normal breast tissue samples.