A significantly decreased mRNA level in the breast cancer tissue samples was observed for CRY2 (β-coefficient -0.424, p<0.0001), PER1 (β-coefficient -0.371, p<0.0001), PER2 (β-coefficient -0.149, p = 0.037) and PER3 (β-coefficient -0.231, p = 0.001). The gene discussed is PER2; the disease is breast cancer.