In western blotting assays, the expression levels of cyclin D1, cyclin E, and CDK4 proteins were concomitantly downregulated in both AMACR-knockdown GIST cell lines (Figure-4C), findings concordant with the result of cell cycle arrest in the G1 phase determined by flow cytometry (Figure-4D). This evidence concerns the gene CDK4 and gastrointestinal stromal tumor.