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

Strong HLA-DR antigen expression on cancer cells relates to better prognosis of colorectal cancer patients, although the precise mechanism is controversial. From an immunological point of view, HLA-DR antigen, induced by interferon (IFN)-gamma, 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-gamma mRNA in the tissue. From another aspect, IFN-gamma has been revealed to suppress c-myc expression in vivo through a stat1-dependent mechanism, which is important for cell growth, cell cycle and chromosome instability. In the present study, strong HLA-DR-positive expression on cancer cells was significantly related to better prognosis for colorectal cancer patients. High IFN-gamma 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-gamma, which induces HLA-DR antigens on the cell surface, also suppresses c-myc expression in situ, and is a possible non-immunological mechanism involved in the better long-term survival of colorectal cancer patients.