Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients : Possible involvement of c-myc suppression by IFN-γ in situ

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Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients, although the precise mechanism is controversial. From an immunologic point of view, HLA-DR antigen, induced by IFN-γ, is required for tumor-associated antigen recognition by CD4+ T cells. For instance, as reported previously, the expression of HLA-DR antigen in normal colorectal epithelium immediately adjacent to cancer coincided significantly with the existence of IFN-γ mRNA in the tissue. From another aspect, IFN-γ has been revealed to suppress c-myc expression in vivo through stat1-dependent mechanism, which is important for cell growth, cell cycle, and chromosome instability. In this study, strong HLA-DR-positive expression on cancer cells, as expectedly, was significantly related to better prognosis of colorectal cancer patients. High IFN-γ mRNA expression in situ indicated significantly less activation of c-myc mRNA expression. Further, HLA-DR antigen expression in cancer cells, as well as Dukes stages, was an independent factor for better long-term survival by multivariate analysis. Taken together, IFN-γ, which induces HLA-DR antigens on the cell surface, also suppresses c-myc expression in situ, and is a possible non-immunologic mechanism involved in the better long-term survival of colorectal cancer patients.