Table 2.

Causes of mismatch repair (MMR) deficiency

	MMR-deficient tumours		Subclonal loss N (%)
	Resections N (%)	Biopsies N (%)	Resections N (%)
MLH1 promoter hypermethylation	30 (40.5)	2 (66.7)	3 (42.9)
Two somatic hits	10 (13.5)	0	1 (14.3)
Lynch syndrome	20 (27.0)	0	0
MLH1 variant	6
MSH2 variant	7
PMS2 variant	2
MSH6 variant	5
MMR variants identified in tumour, normal tissue not available, but high variant allele frequency	6 (8.1)	0	0
MMR deficiency molecularly unexplained (no or only one somatic hit identified)	8 (10.8)	1 (33.3)	3 (42.9)
Total	74	3	7