PER2 and neoplasm: Next, we revealed the coexpression of CCGs in brain tissues (Figures 1(b)–1(d)), according to the coexpression correlations in brain, CCGs were apparently divided into two clusters: cluster I includes ARNTL, NPAS2, CLOCK, and TIMELESS, and another includes CRY1, CRY2, DBP, NR1D1, NR1D2, PER1, PER2, PER3, and RORA. Similar coexpression relationship were found by using the CCD algorithm [23], indicating that the rhythmic oscillation patterns might be also alike in normal brain tissue and tumor samples.