ID	Issue Type	IHC	Molecular	ctMSI	ctCGP	Germline Pathogenic MMR Variant	Status	ICI	ICI Response
	Tissue testing discordance
1	IHC vs. molecular assay	pMMR	MSI-high	Not tested	Not tested	Not tested	MSI	Yes	CR
2	Uncommon IHC (equivocal staining and uncommon pairing)	Equivocal-MSH2/PMS2 (not confirmed)	Not tested	Not tested	Not tested	Not tested	MSS	No
3	Uncommon IHC (equivocal staining)	Equivocal-MSH2 (not confirmed)	Not tested	ctMSS	None	Not tested	MSS	No
4	Uncommon IHC (equivocal staining)	Equivocal-PMS2	MSS	ctMSS	Not tested	None	MSS	No
5	Uncommon IHC (equivocal staining)	Equivocal-PMS2 (not confirmed)	Not tested	Not tested	Not tested	Not tested	MSS	No
6	Uncommon IHC (equivocal staining)	Heterogenous MLH1	MSS	ctMSS	Not tested	Not tested	MSS	No
7	Uncommon IHC (isolated loss and spatial heterogeneity)	dMMR-MSH6 (primary, not confirmed) pMMR (meta)	MSS	Not tested	Not tested	None	MSS	No
8	Uncommon IHC (isolated loss and spatial heterogeneity)	pMMR (primary) dMMR-MSH6 (meta)	MSI-high	Not tested	Not tested	MSH6	MSI	Yes	CR
9	Uncommon IHC (isolated loss and spatial heterogeneity)	pMMR (primary) dMMR-PMS2 (meta)	MSI-high	ctMSS	None	Not tested	MSI	Yes	PR
10	Uncommon IHC (isolated loss)	dMMR-MLH1	Not tested	Not tested	Not tested	Not tested	MSI	No
11	Uncommon IHC (isolated loss)	dMMR-MLH1	Not tested	Not tested	Not tested	Not tested	MSI	Yes	SD
12	Uncommon IHC (isolated loss)	dMMR-MSH6	MSI-high	Non-informative	Non-informative	MSH6	MSI	Yes	CR
13	Uncommon IHC (isolated loss)	dMMR-MSH6	MSI-high	Not tested	Not tested	None	MSI	Yes	CR
14	Uncommon IHC (isolated loss)	dMMR-MSH6	MSI-high	Not tested	Not tested	Not tested	MSI	No
15	Uncommon IHC (isolated loss)	dMMR-MSH6 (not confirmed)	MSS	ctMSS	None	None	MSS	No
16	Uncommon IHC (isolated loss)	dMMR-PMS2	MSI-high	ctMSI-high	None	Not tested	MSI	Yes	CR
17	Uncommon IHC (isolated loss)	dMMR-PMS2	MSI-high	ctMSS	PMS2 c.137G>T (VAF 46%)	PMS2	MSI	Yes	CR
18	Uncommon IHC (isolated loss)	dMMR-PMS2	MSI-high	Not tested	Not tested	Not tested	MSI	Yes	CR
19	Uncommon IHC (isolated loss)	dMMR-PMS2	MSI-low	Not tested	Not tested	Not tested	MSS	Yes	PD
20	Uncommon IHC (isolated loss)	dMMR-PMS2	MSS	ctMSS	None	Not tested	MSS	No
21	Uncommon IHC (isolated loss)	dMMR-PMS2	MSS (Idylla) MSI-high (Pentaplex)	Not tested	Not tested	Not tested	MSI	No
22	Uncommon IHC (spatial heterogeneity)	Equivocal-MLH1/PMS2 (primary) pMMR (meta)	Primary not tested Meta MSS	ctMSS	None	None	MSS	Yes	PD
23	Uncommon IHC (uncommon pairing)	dMMR-MLH1/MSH6	Not tested	Not tested	Not tested	Not tested	MSI	No
	Tissue vs. blood discordance
24	Blood missed	dMMR-MLH1/PMS2	MSI-high	ctMSS	None	None	MSI	No
25	Blood missed	dMMR-MLH1/PMS2	MSI-high	ctMSS	None	None	MSI	Yes	SD
26	Blood missed	dMMR-MLH1/PMS2	MSI-high	ctMSS	None	Not tested	MSI	Yes	PD
27	Tissue missed	pMMR	Not tested	ctMSS	PMS2 W841* (VAF 29.9%)	Not tested	MSI	No
28	Tissue missed	pMMR	MSS	ctMSI-high	Not tested	Not tested	MSI	No
29	Tissue missed	pMMR	Not tested	ctMSS	MSH6 splice site 3801+1G>T (VAF 0.99%)	Not tested	MSI	No
30	Tissue missed	pMMR	Not tested	ctMSS	None	MSH6	MSI	No
31	Tissue missed	pMMR	Not tested	ctMSS	MLH1 S131* (VAF 1.4%)	Not tested	MSI	No
32	Tissue missed	pMMR	Not tested	Not tested	Not tested	PMS2	MSI	No