Microsatellite Unstable Carcinomas Research Articles

Clustered 8-Oxo-Guanine Mutations and Oncogenic Gene Fusions in Microsatellite-Unstable Colorectal Cancer.

PURPOSEColorectal carcinomas (CRCs) with microsatellite-instability (MSI) are enriched for oncogenic kinase fusions (KFs), including NTRK1, RET, and BRAF, but the mechanism underlying this finding is unclear.METHODSThe genomic profiles of 32,218 advanced CRC tumor specimens were analyzed to assess the fusion breakpoints of oncogenic alterations including KFs in microsatellite-stable and microsatellite-unstable CRC. Genomic contexts of such alterations were analyzed to obtain mechanistic insights.RESULTSGenomic analysis demonstrated that oncogenic fusion breakpoints in MSI tumors do not preferentially involve repetitive or low-complexity sequences. Instead, their junction regions showed pronounced guanine and cytosine bias and elevated mutation frequency at G:C contexts. Elevated mutation frequency at G:C bases in relevant introns predicted prevalence of associated oncogenic fusions in MSI CRCs. CRCs harboring mismatch repair signatures had enrichment of butyrate-producing microbial species, reported to be associated with induction of 8-oxoguanine lesions in the intestine.CONCLUSIONDetailed analysis of breakpoints in MSI-associated KFs support a model in which inefficient repair and/or processing of microbiome-induced clustered 8-oxoguanine damage in MSI CRC contributes to the increased incidence of specific oncogenic fusions.

Immunological profiling of molecularly classified high-risk endometrial cancers identifies POLE-mutant and microsatellite unstable carcinomas as candidates for checkpoint inhibition

ABSTRACTHigh-risk endometrial cancer (EC) is an aggressive disease for which new therapeutic options are needed. Aims of this study were to validate the enhanced immune response in highly mutated ECs and to explore immune profiles in other EC subgroups. We evaluated immune infiltration in 116 high-risk ECs from the TransPORTEC consortium, previously classified into four molecular subtypes: (i) ultramutated POLE exonuclease domain-mutant ECs (POLE-mutant); (ii) hypermutated microsatellite unstable (MSI); (iii) p53-mutant; and (iv) no specific molecular profile (NSMP). Within The Cancer Genome Atlas (TCGA) EC cohort, significantly higher numbers of predicted neoantigens were demonstrated in POLE-mutant and MSI tumors compared with NSMP and p53-mutants. This was reflected by enhanced immune expression and infiltration in POLE-mutant and MSI tumors in both the TCGA cohort (mRNA expression) and the TransPORTEC cohort (immunohistochemistry) with high infiltration of CD8+ (90% and 69%), PD-1+ (73% and 69%) and PD-L1+ immune cells (100% and 71%). Notably, a subset of p53-mutant and NSMP cancers was characterized by signs of an antitumor immune response (43% and 31% of tumors with high infiltration of CD8+ cells, respectively), despite a low number of predicted neoantigens. In conclusion, the presence of enhanced immune infiltration, particularly high numbers of PD-1 and PD-L1 positive cells, in highly mutated, neoantigen-rich POLE-mutant and MSI endometrial tumors suggests sensitivity to immune checkpoint inhibitors.

Frequent microsatellite instability in papillary and solid-type, poorly differentiated adenocarcinomas of the stomach

Microsatellite instability (MSI) has been observed in 8-39 % of sporadic gastric cancers. However, despite numerous reports indicating a significant relationship between intestinal-type histology and MSI, detailed correlation between histological subtypes and MSI remains obscure. The purpose of the present study is to clarify the relationship between histological subtype and microsatellite status in gastric carcinomas. Microsatellite status was examined for 464 consecutive gastric carcinomas from 420 patients as well as histological subtypes and other clinicopathological findings. MSI was observed in 82 carcinomas (17.7 %), and the greatest proportions were observed in solid-type, poorly differentiated adenocarcinoma (43.0 %) and papillary adenocarcinoma (32.5 %), both being significantly higher than those of other subtypes. The proportion increased with advancing age (0 % at 51-64 years, 8.5 % at 65-74 years, 18.4 % at 75-84 years, 35.3 % at 85-96 years). Compared with microsatellite-stable carcinomas, microsatellite-unstable carcinomas were significantly related with older age, female gender, antral location, and predominant papillary adenocarcinoma and solid-type, poorly differentiated adenocarcinoma. Poorly differentiated type carcinoma was significantly less frequent than differentiated type in microsatellite-unstable cancer at the early stage, whereas no significant difference existed at the advanced stage. These results suggest that there are specific histological subtypes with highly frequent MSI and that gastric carcinoma with MSI originates from differentiated-type carcinomas, indicating histological diversity during tumor growth.

Sessile Serrated Adenoma With Early Neoplastic Progression

Sessile serrated adenoma (SSA), also referred to as sessile serrated polyp, has been proposed as a precursor lesion to microsatellite unstable carcinoma. However, the mechanism of stepwise progression from SSA to early invasive carcinoma has been unclear. The purpose of this study was to elucidate the histologic characteristics and possible role of p53, β-catenin, BRAF, KRAS, and PIK3CA in the development and progression of SSA. We analyzed 12 cases of SSA with neoplastic progression (SSAN), including 7 cases of intraepithelial high-grade dysplasia (HGD) and 5 cases of submucosal invasive carcinoma, and compared them with 53 SSAs and 66 hyperplastic polyps (HPs) by immunohistochemistry and gene mutation analysis. Histologically, 75% (9 of 12) of SSANs showed tubular or tubulovillous growth patterns rather than serrated ones in the HGD/intramucosal carcinoma component. All 5 SSANs with invasive carcinoma lost their serrated structure and developed increased extracellular mucin in their submucosal carcinoma component, a consistent feature of mucinous adenocarcinoma. Nuclear accumulations of β-catenin and p53 were observed in 50% (6 of 12) and 41.7% (5 of 12) of SSANs, respectively, and were exclusively present in HGD/carcinoma areas. By contrast, neither nuclear β-catenin nor p53 expressions were seen in HPs or SSAs (P<0.0001). BRAF mutations (V600E) were observed in 45.8% (11 of 24) of HPs, 60.9% (14 of 23) of SSAs, and 63.6% (7 of 11) of SSANs, and were equally found in both SSA and carcinoma/HGD areas of the individual SSANs. KRAS exon 1 mutations were uncommon in all 3 groups (4.2%, 4.4%, and 0%, respectively). No mutations of PIK3CA exon 9 or exon 20 were found in any cases that were examined. These findings suggest that BRAF mutations may be associated with the pathogenesis of SSA, but progression to HGD or early invasive carcinoma may be associated with other factors, such as alterations of p53 and β-catenin. In addition, our histologic observations suggest a possible close association between SSAN and mucinous adenocarcinoma.

Pathologic Features and Biologic Importance of Colorectal Serrated Polyps

Serrated polyps of the large intestine comprise a heterogeneous group of mucosal lesions that includes nondysplastic polyps, such as hyperplastic polyps and sessile serrated polyps, and polyps that show overt cytologic dysplasia, namely serrated adenomas and mixed hyperplastic/adenomatous polyps. These polyps have received increased recognition over the past 2 decades, as emerging evidence suggests that a subset may be precursors to colorectal carcinomas that lack chromosomal instability. Several investigators have proposed the concept of the "serrated neoplastic pathway" according to which nondysplastic serrated lesions develop progressively severe dysplasia culminating in the development of microsatellite unstable carcinomas that show DNA hypermethylation and BRAF mutations. A subset of hyperplastic polyps and sessile serrated polyps show mutations in the BRAF gene and abnormal DNA methylation, which can, ultimately, affect the promoter regions of key DNA-repair and tumor suppressor genes, such as MLH1 and MGMT, leading to their decreased transcription and microsatellite instability. On the basis of this hypothesis, many authors have proposed that sessile serrated polyps should be treated and surveilled similar to conventional adenomas, although prospective data are lacking. This review describes the clinicopathologic and molecular features of serrated polyps and discusses the current data regarding their biologic significance.

Genome-wide copy neutral LOH is infrequent in familial and sporadic microsatellite unstable carcinomas

Mismatch repair deficiency in tumors can result from germ line mutations in one of the mismatch repair (MMR) genes (MLH1, MSH2, MSH6 and PMS2), or from sporadic promoter hypermethylation of MLH1. The role of unclassified variants (UVs) in MMR genes is subject to debate. To establish the extend of chromosomal instability and copy neutral loss of heterozygosity (cnLOH), we analyzed 41 archival microsatellite unstable carcinomas, mainly colon cancer, from 23 patients with pathogenic MMR mutations, from eight patients with UVs in one of the MMR genes and 10 cases with MLH1 promoter hypermethylation. We assessed genome wide copy number abnormalities and cnLOH using SNP arrays. SNP arrays overcome the problems of detecting LOH due to instability of polymorphic microsatellite markers. All carcinomas showed relatively few chromosomal aberrations. Also cnLOH was infrequent and in Lynch syndrome carcinomas usually confined to the locus harbouring pathogenic mutations in MLH1, MSH2 or PMS2 In the carcinomas from the MMR-UV carriers such cnLOH was less common and in the carcinomas with MLH1 promoter hypermethylation no cnLOH at MLH1 occurred. MSI-H carcinomas of most MMR-UV carriers present on average with more aberrations compared to the carcinomas from pathogenic MMR mutation carriers, suggesting that another possible pathogenic MMR mutation had not been missed. The approach we describe here shows to be an excellent way to study genome-wide cnLOH in archival mismatch repair deficient tumors.