The expression of CLOCK is markedly increased in breast cancer, as increased expression of differentiated embryonic chondrogenic gene 1 (DEC1) has been associated with increased expression of estrogen receptor α (ERα), which binds to the CLOCK promotor to regulate its transcription (Xue et al., 2020), while BMAL1, PER, and CLOCK levels reduce. The gene discussed is PER1; the disease is breast cancer.