Cyclin D1 belongs to the Cyclin D family. Cyclin D1 is required for the cell cycle G1/S transition. Amplification or overexpression of cyclin D1 plays a pivotal role in the development of various human cancers including breast cancer, colon cancer, melanoma, prostate cancer and lymphoma. Cyclin D1 antibody is useful to differentiate mantle cell lymphoma from small cleaved cell lymphoma. Rabbit monoclonal antibodies to cyclin D1 showed the highest sensitivity to detect this antigen in formalin fixed paraffin embedded tissue as compared to several other clones.