Silencing GTSE1 significantly increased the percentage of S phase owing to the inhibition of mitosis resulting to an S phase arrest in breast cancer cells, meanwhile, the overexpression of GTSE1 increased the percentage of cells in the G2 peak, indicating that overexpression of GTSE1 delayed the M-to-G2 phase transition of breast cancer cells, which is consistent to previous study [14]. The gene discussed is GTSE1; the disease is breast carcinoma.