Malignancies of the uterine corpus and immunoreactivity score of the DNA "mismatch-repair" enzyme human Mut-S-Homologon-2

We analyzed human Mut-S-Homologon-2 expression in normal endometrial tissue (n = 15) and malignancies of the uterine corpus (n = 40). Human Mut-S-Homo logon-2 protein was investigated immunohistochemically on frozen sections, using a highly sensitive streptavidin-peroxidase technique and a specific m ouse monoclonal antibody (clone FE11). Human Mut-S-Homologon-2 labeling pat tern was compared with the staining pattern of the proliferation marker Ki- 67 in the same tumors. A human Mut-S-Homologon-2 immunoreactivity score (hu man Mut-S-Homologon-2-IRS: negative 0-1; weak 2-3; moderate 4-6; strong 8-1 2) for semiquantitative analysis of human Mut-S-Homologon-2 expression is p resented. In normal endometrial tissue samples we found weak nuclear immuno reactivity for human Mut-S-Homologon-2 in 67%, whereas the remaining 33% we re negative for human Mut-S-Homologon-2 (mean hu man Mut-S-Homologon-2-IRS 1.25 +/- 1.29). Al I malignancies of the uterine corpus analyzed revealed m oderate to strong nuclear immunoreactivity (mean human Mut-S-Homologon-2-IR S 9.00, +/- 3.16). Human Mut-S-Homologon-2 staining was heterogeneous, with Visual differences among individual tumor cells. Expression of human Mut-S -Homologon-2 protein was consistently and strongly upregulated in tumor cel ls of malignancies of the uterine corpus compared with normal endometrial t issue (human Mut-S-Homologon-2-PP p < 0.001; human Mut-S-Homologon-2-IS p<0 .001; human Mut-S-Homologon-2-IRS p<0.001). No statistically significant co rrelation in comparing the labeling patterns for human Mut-S-Homologon-2 wi th the labeling patterns for Ki-67 (mean percentage of Ki-67-positive tumor cells 22.00% +/- 17.20) was observed in malignancies of the uterine corpus (human Mut-S-Homologon-2-PP p = 0.443; human Mut-S-Homologon-2-IS p = 0.23 4; human Mut-S-Homologon-2-IRS p = 0.173). Our findings indicate that human Mut-S-Homologon-2 is expressed in normal human endometrial tissue and that expression of human Mut-S-Homologon-2 may be of importance for the genetic stability of malignancies of the uterine corpus in vivo.