MLH1 Promoter Hypermethylation


MLH1 loss determined by IHC is observed in dMMR tumours from both Lynch syndrome patients but also a significant minority of sporadic tumours. MLH1 promoter hypermethylation is a common somatic epimutation in sporadic tumours yet is rare in Lynch syndrome tumours where the ‘first hit’ is inherited. MLH1 promoter hypermethylation can be used to stratify Lynch syndrome risks in patients, particularly those which meet revised Bethesda criteria.

Referral information

We accept biopsies or resection samples from patients with a possible diagnosis of Lynch syndrome. Formalin-fixed paraffin-embedded (FFPE) material should have been reviewed by a pathologist to determine suitability for testing and an estimate of tumour cell content is required. We require either 5 x 5µm unstained, slide-mounted sections or unmounted sections from tissue blocks containing a) tumour tissue and b) normal tissue.  A 30% ratio of neoplastic to normal cells in the submitted pathology sample is required for reliable MLH1 promoter methylation assessment. Samples with lower tumour cell content may be acceptable but wherever possible should be accompanied by a representative H&E stained slide with areas of tumour marked to allow for macrodissection. Please contact the laboratory for guidance if you are unsure whether a sample is suitable. Lymphocyte samples are accepted in order to test for rare cases of Lynch syndrome due to constitutional MLH1 promoter hypermethylation.

Price & reporting times

NHS referrals to this service are paid for where there is an existing specialist commissioning contract for genetic testing.

Test Price (NHS) Price (non-NHS) TRT (calendar days)
MLH1 Promoter Hypermethylation POA POA 28 calendar days

Test validation & quality assurance - information for users

In our study 64/73 (87.7%) of sporadic dMMR tumours showed significant MLH1 hypermethylation whereas only 4/71 (5.6%) of tumours from MLH1 mutation carriers showed significant MLH1 hypermethylation. Although a BRAF mutation at codon 600 is present in the majority of sporadic dMMR tumours, a significant minority, 18/73 (24.6%), had MLH1 hypermethylation alone (Newton et al. 2014).

Sample requirements

5 x 5µM FFPE unstained slide mounted sections (without coverslips) from a tissue block selected to have maximum neoplastic cell content. If neoplastic cell content is less than 20% and the sample is suitable for macrodissection, please send an accompanying H&E stained guide slide prepared from a neighbouring section with the region of neoplasia clearly marked out. Where neoplastic cell content is greater than 30%, 5 x 5 µM FFPE sections as unmounted scrolls in a clean, unused, tube or container manufactured under aseptic conditions is acceptable.

Referral guidelines

Please see our referral guidelines for more information.

Gene(s) - MLH1


1) Deng et al. (1999).Methylation of CpG in a small region of the hMLH1 promoter invariably correlates with the absence of gene expression.Cancer Res 59:2029-2033.

2) Newton et al. (2014). Tumour MLH1 promoter region methylation testing is an effective prescreen for Lynch Syndrome (HNPCC). J Med Genet. 51(12):789-96.