CCNE1 and breast cancer: Furthermore, HQT induced cell cycle arrest at the G2/M phase in breast cancer cells and downregulated the expression of related proteins including CDK1, Cyclin B1, CDK2, and Cyclin E. Additionally, HQT promoted apoptosis in breast cancer cells by upregulating the expression of Bak and CC-3, while downregulating the expression of Bcl-2.