We performed an immunohistochemical analysis of 2 major DNA mismatch repair proteins, human Mut L homologue-1 (hMLH1) and human Mut S homologue-2 (hMSH2), in hepatocellular carcinoma (HCC) using 33 biopsied and 58 surgically resected specimens, as well as 30 samples from non-cancerous livers. In well-differentiated HCCs, the immunoreactivity for these antigens was well preserved, and the staining intensity was stronger compared to the surrounding liver tissues. However, among 41 moderately-differentiated and 9 poorly-differentiated HCCs of the resected cases, hMLH1- and hMSH2-positive cells were significantly reduced in 19 (38%) and 9 (18%) cases, respectively. In 9 resected tumors, the expression of both of these antigens was reduced. Moreover, in 41 tumors of differing histological grades, 10 and 5 tumors for hMLH1 and hMSH2, respectively, contained a less-differentiated area with a reduced number of immunoreactive cells. The samples from non-cancerous biopsied liver and fetal autopsy tissue were well immunostained for both hMLH1 and hMSH2. We confirmed in this series that the hMLH1 and hMSH2 defect did commonly occur in high-grade HCCs, and that it might play a role in tumor progression.</p
