STAT3 and neoplasm: While the frequencies of mitotic cells with supernumerary centrosomes were similar between WT and Stat3−/− tumours, mitotic cells in Stat3−/− tumours had a significantly higher proportion of declustered centrosomes compared to the WT tumours, demonstrating that Stat3 regulates centrosome clustering in tumours in vivo (Fig. 2e; Supplementary Fig. 2f).