High Expression of the Tumor Suppressor Protein ITIH5 in Cholangiocarcinomas Correlates with a Favorable Prognosis

Inter-alpha-trypsin inhibitor-5 (ITIH5), a class II tumor suppressor gene, encodes a protein that is lost during tumor progression in many solid cancers. Unexpectedly, however, ITIH5 is significantly upregulated in cholangiocarcinoma (CCA), making it a potential liquid biopsy marker for early CCA detection, as recently shown. Indeed, CCA is the first tumor entity described in which ITIH5 is upregulated rather than downregulated in the tumor compared to normal tissue. In our study, we demonstrate that CCAs with abundant ITIH5 protein expression have favorable survival, a low UICC stage and the absence of perineural invasion. The re-expression of ITIH5 impairs the colony growth of cholangiocarcinoma cell lines. Although ITIH5 is upregulated in the tumor, it retains its tumor-suppressive function in CCA, similar to other tumor entities such as breast cancer and pancreatic cancer, where it is downregulated. Thus, ITIH5 may have both diagnostic and prognostic biomarker potential in CCA. The mechanisms of ITIH5 upregulation, particularly in intrahepatic CCAs, during oncogenic transformation remain unclear, but their elucidation could improve future CCA therapies.