Several phytochemicals of the different classes of compounds such as alkaloids, flavonoids, saponins, terpenoids, vitamins, glycosides, phenols, et cetera play significant roles in inhibiting or arresting cancer cell progression by different mechanisms such as (a) by inhibiting cancer cell-activating signaling pathways such as Cdc2, CDK2, and CDK4 kinases, topoisomerase enzyme, cyclooxygenase, and COX-2, Bcl-2, cytokines, PI3K, Akt, MAPK/ERK, MMP, and TNK; (b) activating mechanisms of DNA repairing, viz. The gene discussed is CDK4; the disease is cancer.