CD4 and biliary tract neoplasm: In the mature stage of T cells, only one immunophenotype of T-cells in the maturation stage was negatively associated with risk of biliary tract cancer, CD4RA on TD CD4+, which was protective against a reduced risk of biliary tract cancer, as detected by an OR<1 (OR=0.95, 95% CI=0.90–1.00, P=0.034).