To test this, we treated Cal51 triple-negative (negative for estrogen receptor, progesterone receptor, and HER2 amplification) breast cancer cells with either GSK923235 to induce misaligned chromosomes by inhibiting the plus end directed kinesin motor CENP-E or with reversine, an Mps1 inhibitor that accelerates mitotic transit to generate lagging and bridge chromosomes (47). This evidence concerns the gene ESR1 and breast cancer.