Table 1.

Summary of interpretable staining in each biomarker

	Interpretable staining	MMR intact	MMR loss
MSH2	2399 (60.1%)	2363 (98.5%)	36 (1.5%)
MSH6	2488 (62.3%)	2440 (98.1%)	48 (1.9%)
MLH1	1930 (48.3%)	1891 (98.0%)	39 (2.0%)
PMS2	2159 (54.1%)	2115 (98.0%)	44 (2.0%)

Uninterpretable staining includes lack of viable cancer cells, core dropouts from staining or sectioning, insufficient tumour cells and technical fails (apparent loss but without internal positive controls). Refer to Supplemental Table B for detailed distribution