- Background Insulin-like growth factors (IGFs) play an important role in normal and cancerous cell proliferation. Moreover, in recent studies IGF-I has been implicated as a major cancer risk factor. The tomato carotenoid lycopene and all-trans retinoic acid (atRA) have been shown to inhibit growth factor-induced proliferation of different types of cancer cells. This action is associated with inhibition of cell cycle progression in G0/G1 phase. Cyclin D1 acts as a growth factor sensor in G1 phase and is overexpressed in many breast cancer tumors. We have previously demonstrated that slowdown of serum-stimulated cell cycle progression from G1 to S phase by lycopene correlates with reduction in cyclin D1 levels, suggesting that the expression of this protein is a main target for lycopene’s action.