This is because variations in the PER gene (denoted as P0,P1,P2 in drosophila and as P1,P2,P3 in human) may affect disruption in the cell cycle via the cMyc pathway with PER, ATK pathway with PER1 and estrogen signal, and HER with PER mutants; these pathways are known to be signature for progression of cancer in organs such as breast (Konopka and Benzer, 1971). Here, PER1 is linked to cancer.