Huang CY, et al. - The current study explored the anti-cancer impact of palbociclib combined with radiation therapy (RT) for the treatment of human hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), as well as the molecular mechanism behind the combination therapy. To determine the impact of palbociclib on double-strand break (DSB) repair, immunofluorescence staining of γH2AX or 53BP1 was used. Researchers found that palbociclib influenced the kinetics of DNA repair and heightened the radiation sensitivity of HCC and CCA cells. It was noted that palbociclib inhibits ataxia telangiectasia–mutated (ATM) kinase, the key upstream kinase responding to RT-induced DSBs. Findings revealed that RT plus palbociclib shows synergy in liver cancer cells.