PER1 and neoplasm: Three weeks after subcutaneous injection of untreated SCC15 cells or cells expressing PER1-shRNA-I into the backs of 10 nude mice, the tumor weights (volumes) in the PER1-shRNA-I and SCC15 groups were respectively 0.48±0.04g (0.28±0.09 cm3) and 0.19±0.07 g (0.10±0.08 cm3) (P<0.05) (Figure 5A-5C).