The cell cycle is a tightly regulated biological process that governs cell growth and division through sequential phases including G1, S, G2, and M. This progression is controlled by a complex regulatory network composed of cyclins, cyclin-dependent kinases (CDKs), and checkpoint proteins that ensure genomic integrity and proper cell division.



In cancer biology, dysregulation ofoncoproteins in cell cycle regulation and tumor proliferation is a fundamental hallmark. Oncoproteins derived from mutated or overexpressed oncogenes can override normal checkpoint controls, leading to uncontrolled cell division and genomic instability. These proteins promote tumorigenesis either by accelerating cell cycle progression or by inhibiting tumor suppressor pathways such as p53 and Rb signaling.



Key regulators such as Cyclin D1 (CCND1) and CDK4 are central components of the cell cycle G1/S transition biomarkers in cancer research. The Cyclin D1–CDK4 complex phosphorylates the retinoblastoma (Rb) protein, releasing E2F transcription factors and initiating DNA synthesis. Overexpression or amplification of CCND1, as well as aberrant activation of CDK4, has been widely observed across multiple cancer types, including breast, lung, and hematologic malignancies, highlighting their role as critical drivers of tumor proliferation.