DETECTING LYNCH SYNDROME IN A NATIONAL COLORECTAL CANCER SCREENING PROGRAMME

Aims Lynch Syndrome(LS) is the most common cause of hereditary colorectal cancer(CRC) accounting for 2-4% of all CRCs. It is characterised by pathogenic variants in mismatch repair(MMR) genes. Many people are unaware of their diagnosis. Universal testing of all CRCs has been recommended to address this. The aim was to determine the proportion of CRCs tested for LS at two screening sites of the Irish national CRC screening service, BowelScreen, and to examine the outcomes of testing.

Methods CRCs diagnosed through BowelScreen from 2015 to 2020 were identified. Histopathology reports and electronic patient records were used to determine if CRCs were tested for LS with immunohistochemistry for MMR deficiency(dMMR) and if dMMR was found whether further testing to rule out LS or genetic testing to confirm LS were undertaken.

Results 207 CRCs were identified. Site A tested 100% of CRCs with IHC. Site B tested 69% of CRCs overall, however 100% in 2020 were tested.

Table 1. Numbers of CRCs tested for LS for 2015 vs 2020, by screening site.

Table 1

	Site A – n(%)	Site B – n(%)	Totals – n(%)
2015	22 (100%)	8 (57.1%)	30 (83.3%)
2020	3 (100%)	5 (100%)	8 (100%)

14(6.7%) were MMR deficient. 13(93%) had combined loss of MLH1/PMS2. 11/13(84.6%) were determined to be sporadic based on either BRAFV600E mutation or hypermethylation of the MLH1 promotor region. MSH6 loss was detected in 1 CRC. In total 3 patients were eligible for germline testing. 1 declined and 2 did not have follow up documented.

Fig. 1

Conclusions Both sites had implemented universal testing for LS by 2020 in line with international guidance. A small number of patients were eligible for germline testing however only 33% were referred, highlighting the need for appropriate resources and referral pathways within our national screening programme.

Publication History

Article published online:
14 April 2022