Table 4.

Immunohistochemistry (IHC) results and possible causes [13,63].

IHC Results	Interpretation
Retained MMR proteins expression	(a) When MSI-H tumor—germline mutation in MMR/EPCAM genes but possibly maintained protein expression (b) when MSI−L/MSS-sporadic cancer
Heterogeneity of MMR protein expression	If heterogeneity is observed despite proper performance of IHC, it might be reasonable to consider further molecular testing.
Loss of MSH2 protein expression	Germline MSH2 mutation
Loss of MSH6 protein expression	Germline MSH6 mutation, rarely MSH2
Loss of MSH2 and MSH6 protein expression	Germline MSH2/EPCAM mutation, rarely MSH6
Loss of MLH1 and PMS2 protein expression	Sporadic cancer or germline MLH1 mutation—recommendation: further BRAF/MLH1 methylation testing
Loss of MLH1 protein expression	Germline MLH1 mutation
Loss of PMS2 protein expression	Germline PMS2 mutation, rarely MLH1