FIS1 and cancer: Mitochondria are highly dynamic organelles that are continually undergoing fission and fusion.20 Altered mitochondrial dynamics have been linked to abnormal cell functions21,22 and many human diseases,23–26 including cancers.26,27 Studies have shown that excess mitochondrial fission28,29 and upregulation of the fission component Fis1-Drp1 are frequently involved in tumorigenesis and metastasis.28,30–32 How mitochondrial fission regulates cancer cell movements remains elusive.