Cyclin D1 (CCND1) is a central regulator of the G1/S cell cycle transition, functioning through CDK4/6-mediated phosphorylation of Rb to promote cell proliferation. Aberrant Cyclin D1 overexpression or gene amplification is frequently observed in malignancies such as breast cancer, mantle cell lymphoma, lung cancer, and colorectal cancer, where it drives tumor progression, therapeutic resistance, and adverse clinical outcomes. Beyond its canonical CDK-dependent role, Cyclin D1 also modulates transcriptional programs, cellular metabolism, and oncogenic signaling pathways, underscoring its value as both a biomarker and a critical research target in cancer biology. Catalina’s high-quality Cyclin D1 antibodies offer exceptional specificity and sensitivity, providing reliable tools for cancer research, biomarker studies, and drug discovery focused on cell cycle regulation and oncogenic mechanisms.