A significantly decreased expression of cyclins D1, D3, E, A, and B1 in cancerous cells was recorded after incubation of cells with 90 μM silybin A and B. The authors then compared individual substituents of the silymarin complex and found that only silybin A and B and isosilybin A and B had a down-regulating effect on the cell cycle, while silydianin, silychristin, and isosilychristin did not affect the cell cycle of cancer cells. This evidence concerns the gene CCND1 and cancer.