We then evaluated changes in the expression of components of the core clock machinery (BMAL1, CLOCK, PER1/2/3, CRY1/2, NR1D1/2, and DEC1/2) and three clock output genes (WEE1, TEF, DBP) upon knockdown or overexpression of KLF9 in normal MCF10A cells and in the highly aggressive MDA-MB-231 cancer line. The gene discussed is PER1; the disease is cancer.