PER2 and neoplasm: After 4 weeks, IVIS (in vivo imaging system) analysis showed that U87-Per2 OE tumor size was less than control, the U87-Id3 OE group was obviously larger than control, while the U87-Id3 OE+Per2 OE group was visibly restrained compared to the U87-Id3 OE group, suggesting that Per2 OE slows tumor growth (Figure 5a, b).