CDK4 and neoplasm: Furthermore, HE staining showed that tumors treated with the triple combination contained large areas of degeneration and reactive fibrosis (within the indicated circles) surrounded by vital tumor tissue, while only small areas of degeneration and reactive fibrosis were observed in tumors treated with combined CDK4/6i and fulvestrant, and the vital tumor tissue areas were much larger in these tumors (Supplementary Fig. S4H).