Table 2.

Available immunohistochemistry groups in the MSI-H cases: Group 1 (MSI-H and age < age 50 years) and Group 2 (MSH-H, age > 49 years). These results suggest the age cut-offs did create groups that were more (Group 1) and less (Group 2) likely to have germline mutations underlying the MSI phenotype. Germline testing, tumor BRAF status, and tumor MLH1 methylation results were not sufficiently consistently available at the time of this study to further refine these groups while maintaining adequate sample sizes.

	Group 1	Group 2
MLH1
# samples with interpretable results	89	273
# samples with loss of expression	41	213
% interpretable samples with loss of expression	46%	78%
MSH2
# samples with interpretable results	87	281
# samples with loss of expression	35	30
% interpretable samples with loss of expression	40%	10.7%
MSH6
# samples with interpretable results	72	247
# samples with loss of expression	2	9
% interpretable samples with loss of expression	3.6%	3%
PMS2
# samples with interpretable results	59	171
# samples with loss of expression	3	8
% interpretable samples with loss of expression	5%	4.7%