Immunohistochemistry using monoclonal antibody MsMab-2 is useful to detect IDH1 R132L in intrahepatic cholangiocarcinoma.

Immunohistochemical analysis using specific antibodies is a useful and convenient method to detect proteins altered by somatic mutations. We previously generated the rat monoclonal antibody MsMab-2, which recognizes isocitrate dehydrogenase (IDH)1 R132L and IDH2 R172M. In the present study, we used an immunohistochemical method to examine MsMab-2 immunoreactivity in 95 cases of intrahepatic cholangiocarcinoma, including five IDH1 R132L and one IDH2 R172M mutant cases confirmed by direct sequencing. Tissue microarray section slides of all IDH1/2-mutant and wild-type cases, as well as whole section slides of IDH1 R132L and IDH2 R172M cases were immunostained using an autostainer. All IDH1 R132L cases showed positive staining for MsMab-2, while other IDH1/2 mutant and IDH1/2 wild-type cases were negative. Tumor cells of the immunopositive cases invariably showed strong reactivity using whole-section slides. We consider immunohistochemical analysis using MsMab-2 to be a useful means of detecting IDH1 R132L. Further analysis of its effectiveness against IDH2 R172M is necessary because of the small sample size in this study.