The study investigates the mechanism linking extra centrosomes to chromosomal instability (CIN) in cancer cells. It is proposed that extra centrosomes promote CIN by facilitating multipolar anaphase, which produces aneuploid daughter cells. However, the authors find that multipolar divisions are rare and often result in inviable progeny, suggesting that they cannot explain the high rates of CIN. Instead, they observe that cells with extra centrosomes undergo bipolar divisions but have a significantly increased frequency of lagging chromosomes during anaphase. Through live-cell imaging and genetic manipulation, they demonstrate that extra centrosomes alone can promote chromosome missegregation during bipolar cell division by creating transient multipolar spindle intermediates where merotelic kinetochore-microtubule attachments accumulate. These findings provide a direct mechanistic link between extra centrosomes and CIN, suggesting that this mechanism may be a common cause of chromosomal instability in human cancer.The study investigates the mechanism linking extra centrosomes to chromosomal instability (CIN) in cancer cells. It is proposed that extra centrosomes promote CIN by facilitating multipolar anaphase, which produces aneuploid daughter cells. However, the authors find that multipolar divisions are rare and often result in inviable progeny, suggesting that they cannot explain the high rates of CIN. Instead, they observe that cells with extra centrosomes undergo bipolar divisions but have a significantly increased frequency of lagging chromosomes during anaphase. Through live-cell imaging and genetic manipulation, they demonstrate that extra centrosomes alone can promote chromosome missegregation during bipolar cell division by creating transient multipolar spindle intermediates where merotelic kinetochore-microtubule attachments accumulate. These findings provide a direct mechanistic link between extra centrosomes and CIN, suggesting that this mechanism may be a common cause of chromosomal instability in human cancer.