Neoplastic diseases, including lung cancer are characterized by an uncoordinated cell growth. Cellular proliferation follows an orderly progression through the cell cycle, which is governed by protein complexes composed of cyclins and cyclin-dependent kinases. These complexes exert their regulatory function by phosphorylation of key proteins involved in cell cycle transitions. Abnormalities of cyclins and cyclin-dependent kinases have been reported and proposed to be oncogenic events. It appears that the molecular networking of these proteins and complexes exerts an impact on two fundamental cell cycle regulators; p53 and pRb. Interactions between these two nuclear proteins are being delineated, implying potential links between p53 and Rb in cell cycle control, apoptosis, and tumor progression. Furthermore, the detection of alterations in p53 and Rb pathways appears to be of clinical significance.