CLOCK and cancer: Recent researches have shown that PIWIL1 is involved in tumorigenesis,29, 30, 31 meanwhile, the tumorigenesis is associated with circadian rhythms in humans.21, 22 Then our immunoprecipitation results showed that PIWIL1 can interact with circadian core proteins CLOCK and BMAL1 in cancer cells, suggesting the linkage between PIWIL1 and circadian rhythms.