HLA heterozygous deletion is a mechanism of tumor immune escape that can lead to a lack of immune recognition of the tumor, resulting in immune resistance to that tumor. HLA refers to human leukocyte antigen is the expression product of the human histocompatibility complex, and HLA is usually also present on the surface of tumor cells, where it is involved in antigen recognition and presentation.HLA is an essential part of the process of tumor cell recognition by CD8-positive T cells. HLA in the human body is encoded by two sets of genes from the mother and the father. When a mutation occurs that results in the total or partial deletion of all or part of the genes coding for one set of HLA, it is known as a heterozygous deletion of HLA, which can lead to errors in the process of recognizing the tumor cells by CD8-positive T-cells, and thus failing to correctly recognize the tumor cells, leading to immune escape of the tumor cells and consequently to immune drug resistance.