CD4+ T cells have two subsets—Th 1 and Th 2 cells—and some clinical data observed unbalanced Th 1/Th 2 levels in patients with breast cancer, where Th 2 cells released the cytokines IL-4 and IL-10 and suppressed the host immune system, exhibiting a tumour-promoting effect [51]. This evidence concerns the gene IL4 and breast cancer.