CHEK1 and osteosarcoma: Recent studies also showed in human osteosarcoma cells that Mus81 is dependent in cell cycle defects and replication fork collapse caused by CHK1 inhibition and Mus81 depletion alleviates the S‐phase progression defects and decrease cell death induced by CHK1 deficiency 32, which to some extent agreeing with our results obtained in HCC cells that CHK inhibition could rescue the S‐phase arrest and apoptosis induced by Mus81 knockdown.