When considering ORR, the addition of chemotherapy to palbociclib significantly improved the quality of antitumor responses in squamous-cell carcinomas (13% of palbociclib-treated mice had ORR < −0.75 versus 63% of combination-treated mice), but not in ADCs, despite the presence of RB1 alterations (a potential biomarker of palbociclib resistance) in squamous-cell carcinomas (Figure 5c,d). This evidence concerns the gene RB1 and squamous cell carcinoma.