PER2 and pituitary gland adenoma: Notably, six cell cycle genes [i.e., Ccna1 (cyclin A1), Ccnb2, Cdc20, Cdkn2a (cyclin dependent kinase inhibitor 2A), E2f1 (E2 promoter binding factor 1), and Espl1] were commonly found in enriched pathways of both cell cycle and HTLV-1 infection (Figure 4C), suggesting involvement of cell cycle disturbance in PER2 regulation of pituitary adenoma.