Mononucleotide precedes dinucleotide repeat instability during colorectal tumour development in Lynch syndrome patients

Abstract

A progressive accumulation of genetic alterations underlies the adenoma-carcinoma sequence of colorectal cancer. This accumulation of mutations is driven by genetic instability, of which there are different types. Microsatellite instability (MSI) is the predominant type present in the tumours of Lynch syndrome patients and in a subset of sporadic tumours. It is generally accepted that MSI can be found in the early stages of tumour progression, such as adenomas; however, the frequencies reported vary widely among studies. Moreover, data on the qualitative differences between adenomas and carcinomas, or between tumours of hereditary and sporadic origin, are scarce. We compared MSI in samples of colorectal adenoma and colorectal carcinoma in order to identify possible differences along the adenoma-carcinoma sequence. We compared germline mismatch repair (MMR) gene mutation carriers and non-carriers, to address possible differences of instability patterns between Lynch syndrome patients and patients with sporadic tumours. We found a comparable relative frequency of mono- and dinucleotide instability in sporadic colorectal adenomas and carcinomas, dinucleotide instability being observed most frequently in these sporadic tumours. In MMR gene truncating mutation carriers, the profile was different: colorectal adenomas showed predominantly mononucleotide instability and in colorectal carcinomas, also more mononucleotide than dinucleotide instability was detected. We conclude that MSI profiles differ between sporadic and Lynch syndrome tumours, and that mononucleotide marker instability precedes dinucleotide marker instability during colorectal tumour development in Lynch syndrome patients. As mononucleotide MSI proves to be highly sensitive for detecting mutation carriers, we propose the use of mononucleotide markers for the identification of possible Lynch syndrome patients.

Challenging cases encountered in colorectal cancer screening for Lynch syndrome reveal novel findings: nucleolar MSH6 staining and impact of prior chemoradiation therapy

“…Although this test has reported sensitivities as low as 58%, more recent studies that use solely or predominantly mononucleotide markers show the highest sensitivities (up to 100%) [13,19,20,[26][27][28][29][30]. Although historical studies have noted that the performance of MSI testing is poorest for MSH6 mutation carriers [19,26,29,31,32], more recent studies that recommend the use of quasimonomorphic mononucleotide repeats show increased sensitivity and specificity of MSI testing and increased detection of MSH6 mutation carriers [29,30,33,34]. An additional reason for switching to mononucleotide markers is that MSI can produce false-positive results, often in the dinucleotide markers [30,33,35].…”

Microsatellite Instability and DNA Mismatch Repair Protein Deficiency in Lynch Syndrome Colorectal Polyps

“…(24) This panel has recently been shown to have superior sensitivity and specificity for detecting LS-associated CRCs compared to the National Cancer Institute (NCI)-endorsed panel, which uses two mononucleotide markers (BAT-25 and BAT-26) and three dinucleotide markers (D2S123, D17S250, and D5S346). (18, 25) Unlike the NCI-endorsed panel, this pentaplex PCR can be performed as a single reaction and does not require simultaneous analysis of corresponding germline DNA from subjects. (24) Polyps were considered to have high-level microsatellite instability (MSI-H) if ≥40% of the markers that gave results were unstable.…”

On the advent of MSI testing of all colorectal cancers and a substantial part of other Lynch syndrome-related neoplasms

“…This pooling of samples, and, when possible, centralization, will increase the efficiency of the determinations and will create possibilities for robotization of DNA isolation and molecular analyses and for (semi-)automatic result evaluation. In addition, the use of multiplex PCR assays with mononucleotide microsatellites can increase the specificity, sensitivity and efficiency of the MSI tests [23][24][25]. The (semi-)automated large-scale screening of all newly diagnosed CRCs will lead to decreased costs for analysis, especially for the molecular determinations.…”

“…The (semi-)automated large-scale screening of all newly diagnosed CRCs will lead to decreased costs for analysis, especially for the molecular determinations. Therefore, it can be anticipated that LS screening by both MMR IHC and MSI analysis becomes cost effective for all newly diagnosed CRCs and possibly also for endometrial and other LS malignancies (probably with an age criterion) and advanced colorectal adenomas (advancement based on dysplasia, size, villous features, or number criteria, with an age criterion) [23]. Furthermore, it is theoretically (and also in practice, depending on the clinical and laboratory logistics and infrastructure) possible to perform the LS-diagnostic analyses on the preoperative biopsies.…”

“…Offering MMR-IHC testing to all newly diagnosed patients with CRC is currently recommended in Denmark and discussed in several other European countries [19]. Potential problems with the procedure of testing all newly diagnosed CRCs by MMR IHC are that interpretation of the IHC results is only reliable in a specialized setting [20] and, in addition, the combined application of MMR IHC and MSI analysis is still considered the most sensitive procedure to detect LS [21,22], especially when mononucleotide microsatellites instead of dinucleotide markers are used [23].…”