Lynch syndrome (LS) is caused by a pathogenic heterozygous germline variant in one of the DNA mismatch repair (MMR) genes: MLH1, MSH2, MSH6 or PMS2. LS-associated colorectal carcinomas (CRCs) are... Show moreLynch syndrome (LS) is caused by a pathogenic heterozygous germline variant in one of the DNA mismatch repair (MMR) genes: MLH1, MSH2, MSH6 or PMS2. LS-associated colorectal carcinomas (CRCs) are characterized by MMR deficiency and by accumulation of multiple insertions/deletions at coding microsatellites (cMS). MMR deficiency-induced variants at defined cMS loci have a driver function and promote tumorigenesis. Notably, PMS2 variant carriers face only a slightly increased risk of developing CRC. Here, we investigate whether this lower penetrance is also reflected by differences in molecular features and cMS variant patterns. Tumor DNA was extracted from formalin-fixed paraffin-embedded (FFPE) tissue cores or sections (n = 90). Tumors originated from genetically proven germline pathogenic MMR variant carriers (including 14 PMS2-deficient tumors). The mutational spectrum was analyzed using fluorescently labeled primers specific for 18 cMS previously described as mutational targets in MMR-deficient tumors. Immune cell infiltration was analyzed by immunohistochemical detection of T-cells on FFPE tissue sections. The cMS spectrum of PMS2-deficient CRCs did not show any sig-nificant differences from MLH1/MSH2-deficient CRCs. PMS2-deficient tumors, however, displayed lower CD3-positive T-cell infiltration compared to other MMR-deficient cancers (28.00 vs. 55.00 per 0.1 mm(2), p = 0.0025). Our study demonstrates that the spectrum of potentially immunogenic cMS variants in CRCs from PMS2 gene variant carriers is similar to that observed in CRCs from other MMR gene variant carriers. Lower immune cell infiltration observed in PMS2-deficient CRCs could be the result of alternative mechanisms of immune evasion or immune cell exclusion, similar to those seen in MMR-proficient tumors. Show less
Suerink, M.; Rodriguez-Girondo, M.; Klift, H.M. van der; Colas, C.; Brugieres, L.; Lavoine, N.; ... ; Nielsen, M. 2019
Colorectal cancer is one of the most frequently diagnosed cancers in the Western world. Both hereditary and genetic factors play a role in its etiology. In approximately 3% of colorectal cancer... Show moreColorectal cancer is one of the most frequently diagnosed cancers in the Western world. Both hereditary and genetic factors play a role in its etiology. In approximately 3% of colorectal cancer cases the underlying cause is a hereditary cancer predisposition syndrome called Lynch syndrome. This thesis focuses on an important subset of Lynch syndrome patients, namely those carrying a mutation in the mismatch repair gene PMS2. Relatively little was known about PMS2-associated Lynch syndrome compared to Lynch syndrome caused by other genes. We provide evidence that PMS2 carriers should be considered a separate entity among Lynch patients. First off, PMS2 carriers have a lower penetrance for colorectal and endometrial cancer. Moreover, they are not at increased risk of other Lynch-associated cancers, such as ovarian cancer. The reason for relatively low colorectal cancer penetrance was investigated by analyzing the somatic mutation spectrum of these tumors. This indicated that PMS2 carriers may not develop cancer from so-called mismatch repair deficient crypts. Lastly the effect of lifestyle and single-nucleotide-polymorphisms (SNPs) was investigated which revealed no significant influence on colorectal cancer risk. The results of the studies described in this thesis have resulted in reconsideration of surveillance guidelines of PMS2-associated Lynch syndrome patients. Show less
Suerink, M.; Potjer, T.P.; Versluijs, A.B.; Broeke, S.W. ten; Tops, C.M.; Wimmer, K.; Nielsen, M. 2018
