CCNE1 and breast cancer: The siRNA-mediated decrease of either E-cyclin severely attenuates the estrogen-induced proliferation of breast cancer cells [75], and the reduction of either cyclin E1 or E2 leads to reduced colony forming ability in oral squamous cell carcinoma cells, although cyclin E1 ablation is more potent than ablation of cyclin E2 (70% vs 20% reduction) [97].