The immune response is a critical factor in regulating tumor growth; however, patients with advanced cancer often exhibit a poorly functioning immune response, which manifests as decreased T cell proliferation, a reduced CD4 : CD8 ratio, alterations in signal transducing molecules (such low CD3ζ expression in T cells and expression of MHC class I in the tumor cells), and deficient cellular immune response production of Th1 cytokines, changes which correlate with the severity of the disease [3, 4]. The gene discussed is CD4; the disease is neoplasm.