HLA-A and cancer: There are also HLA III gene regions, which contain genes encoding complement components C2, C3 and C4 and B factors, etc. An increasing number of studies have shown that HLA alleles are associated with certain diseases, and HLA-A are known to be related to immune response pathways in different cancers, among which HLA-A * 33 is associated with susceptibility to HBV infection [5].