Peter Zauber

Peutz-Jeghers disease: most, but not all, families are compatible with linkage to 19p13.3.

A locus for Peutz-Jeghers syndrome (PJS) was recently mapped to chromosome 19p13.3. Each of 12 families studied was compatible with linkage to the marker D19S886. We have analysed 20 further families and found that the majority of these are consistent with a PJS gene on 19p13.3. Three families were, however, unlinked to 19p13.3 and none of the available PJS polyps from these families showed allele loss at D19S886. There were no obvious clinicopathological or ethnic differences between the 19p13.3 linked and unlinked families. There appears, therefore, to be a major PJS locus on chromosome 19p13.3 and the possibility exists of a minor locus (or loci) elsewhere.

Ki-ras gene mutations are invariably present in low-grade mucinous tumors of the vermiform appendix

Abstract Objective. Low-grade mucinous tumors of the appendix appear to have a simple histological structure. Paradoxically, reports have suggested a greater frequency of Ki-ras gene mutation in these lesions than in more complex lesions such as benign colonic adenomas and carcinomas. We assessed several molecular genetic changes, including Ki-ras gene mutations, in a large series of low-grade mucinous tumors of the appendix. Material and methods. We retrospectively ascertained low-grade mucinous tumors of the appendix from computerized pathology records. Extracted DNA was analyzed for APC and DCC gene loss of heterozygosity, microsatellite instability and for the presence of Ki-ras gene mutation using standard molecular techniques. Controls consisted of normal appendices, other appendiceal neoplasms, and ovarian mucinous cystadenomas. Results. A total of 31 low-grade appendiceal mucinous tumors were identified. All were microsatellite stable and none demonstrated loss of heterozygosity for the APC or DCC genes. By contrast, all 31 lesions contained a Ki-ras gene mutation. Conclusions. The presence of a Ki-ras gene mutation in all lesions, with no other molecular changes identified, strongly suggests a possible etiological role of the Ki-ras mutation in the development of this particular lesion of the appendix. Based on other work regarding intestinal bacteria, we hypothesize a relationship between chronic inflammation of the appendix from bacterial overgrowth and Ki-ras gene mutation.

Similarities of Molecular Genetic Changes in Synchronous and Metachronous Colorectal Cancers Are Limited and Related to the Cancers’ Proximities to Each Other

Synchronous and metachronous colorectal cancers are distinct primary neoplasms diagnosed either simultaneously or sequentially in the same patient. Because they arise in a common genetic and environmental background, they offer a unique opportunity to study molecular genetic changes occurring during carcinogenesis. We evaluated tumors from 50 patients with synchronous and five additional patients with metachronous cancers for loss of heterozygosity of the genes APC and DCC, KRAS and BRAF gene mutations, and microsatellite instability and methylation. Standard PCR methods were used. Approximately two thirds of the synchronous tumors that were informative for each of the five primary molecular genetic changes showed the same results when located in the same colon segment. However, there was less consistency of molecular findings for the synchronous pairs separated by one or more colonic segments, with half or more of these pairs showing different molecular results. Metachronous tumors also showed variation of molecular genetic findings, but this was less when the subsequent tumor was close to the segment of the first tumor. Molecular genetic findings between synchronous and metachronous tumors can be different, even for tumors sharing the same microenvironment of the same colon segment. These findings support the concept that a mutagen might produce different genetic pathways in two proximate tumors.

Strong correlation between molecular changes in endometrial carcinomas and concomitant hyperplasia.

Objective Endometrial cancer (EC) results from the accumulation of numerous genetic abnormalities contributing to the progression from hyperplasia to EC. Information on these various genetic changes has been primarily derived from studying groups of either hyperplasias or cancers. We evaluated both hyperplastic and EC tissue obtained from the same surgical specimens for KRAS mutations, microsatellite instability (MSI), and mismatch repair gene methylation, and results were correlated between the paired hyperplastic tissue and EC. The aim was to determine if molecular alterations appearing in ECs might also be present in the premalignant (hyperplastic) region of the tumor. Methods One hundred ninety-seven cases of EC with associated hyperplasia were evaluated. DNA samples were studied using primer sets for KRAS gene codons 12/13 and for MSI utilizing the Bethesda panel. Methylation testing was performed on specimens that were microsatellite unstable using the MRC Holland SALSA MS-MLPA methylation-specific DNA detection kit. Results Forty-one (20.8%) of 197 cancers demonstrated a KRAS mutation, with 35 (85.4%) of 41 accompanying hyperplasias also containing a KRAS mutation. Forty-five cancers (22.8%) were microsatellite unstable, with 38 (84.4%) of 45 accompanying hyperplasias also demonstrating instability. Of the 45 microsatellite unstable cancers, 28 (62.2%) demonstrated methylation in both the cancer and the accompanying hyperplasia, whereas 9 pairs (20%) showed no methylation for either the cancer or hyperplasia. Conclusions Approximately 95% of endometrial specimens demonstrated identical molecular findings regarding KRAS mutation and microsatellite stability in the paired cancer and hyperplastic tissue. The same methylation pattern was found in 82.2% of the studied paired samples. Our findings strongly suggest that the molecular changes of KRAS mutation, MSI, and methylation occur early in the neoplastic process. We propose that endometrial biopsies revealing only hyperplasia should be studied for these molecular alterations as an indicator of possible early carcinogenesis.

GNAS mutations are associated with mucin production in low-grade appendiceal mucinous neoplasms, villous adenomas, and carcinomas

We read with interest the article by Singhi et al [1] in a recent issue of Human Pathology. The authors reported that a GNASmutation was present in about one-third of both lowgrade and high-grade disseminated appendiceal mucinous neoplasms, and thus, GNAS mutation cannot be used to distinguish between lowand high-grade neoplasms. These tumors are uncommon, and there are limited reported data on the underlying molecular changes in appendiceal mucinous tumors.Wepreviously reported 100%KRASmutations in a cohort of 31 low-grade appendiceal mucinous neoplasms [2]. Using polymerase chain reaction techniques to evaluate the codon 201 region of exon 8 of theGNAS gene, a subsequent evaluation of our tumors has revealed aGNASmutation in 17 (53.1%) of our 32 mucinous neoplasms. The GNAS mutations were closely divided: 9 were R201C, and 8 were the R201H variant. A total of 8 surgical specimens from the 15 (53.3%) tumors with a GNAS mutation demonstrated excess mucin. Five of the 8 had a simultaneous mucinous cystic lesion involving the ovary, interpreted by the surgical pathologist to have originated in the appendix. The other 3 contained omental mucin. Only 2 (13.3%) of the 15 tumors with wild-type GNAS demonstrated mucin beyond the appendiceal lumen, both with peritoneal implants. We also studied 6 villous adenomas of the appendix, and all contained a GNAS mutation. However, of 9 adenocarcinomas of the appendix, only 2 were mutated, and one of these 2 contained copious mucin histologically. Recent large-scale systematic analyses of variants in cancer have revealed numerous potential candidate cancer genes. One such study identified a nonsynonymous base change at codon 201 of the α-subunit of the stimulatory G protein (GNAS) [3]. This protein serves as a ubiquitously expressed signal transducer that transmits hormonal and growth factor signals to effector proteins, particularly activation of the membrane-associated enzyme adenylate cyclase [4]. Mutations that occur at GNAS codon 201 have been shown to constitutively activate the gene and lead to constitutive cAMP signaling. Other in vitro studies suggest that mutant GNAS might play a direct role in prominent mucin production, the hallmark of appendiceal mucinous neoplasms [5]. Our results provide significant clinical evidence for a relationship between GNAS mutations and mucin production in appendiceal tumors, both the low-grade mucinous neoplasms as well as appendiceal villous adenomas and adenocarcinomas. Our results further suggest that it would be of interest to evaluate other mucinous tumors for possible GNAS genetic changes.

Colorectal tumors from APC*I1307K carriers principally harbor somatic APC mutations outside the A8 tract.

Purpose APC*I1307K (c.3920T>A) is an inherited variant associated with colorectal tumour risk found almost exclusively in those of Ashkenazi Jewish ancestry. A single nucleotide substitution creates an oligo-adenine tract (A8) that appears to be inherently prone to further mis-pairing and slippage. The reported multiple tumor phenotype of carriers is not easily reconciled with molecular and population genetics data. We postulated that some c.3920T>A carriers with multiple adenomas have other unidentified APC germ line or somatic mutations. Methods DNA from 82 colonic tumours and accompanying normal tissue collected from 29 carriers with multiple colorectal tumors was directly sequenced between codons 716 and 1604. We also assessed APC gene loss of heterozygosity. Results One patient (3.4%) was found to have an additional APC germ line mutation. Twenty-five of the tumours showed no significant somatic molecular change, 36 showed one change, 20 showed two, and one tumour showed more than 2 changes. Our data suggest a correlation between advancing histology and fewer beta-catenin binding sites remaining in the mutant proteins. Conclusions There were no other common germ line variants identified within the region of the APC gene examined, suggesting that any effect from this region on tumour production is attributable to the c.3920T>A allele. Our findings further suggest the only somatic genetic change clearly attributable to the c.3920T>A mutation is the c.3924_3925insA.

Detailed molecular genetics of the APC*E1317Q mutation in tumor tissue suggest it may not be pathologically significant.

APC*E1317Q is a low-penetrance variant of the APC gene suggested as a risk for the development of colorectal adenomas and carcinomas. There is very little in the literature describing the molecular details of APC*E1317Q in tumor tissue. We provide information about the molecular genetics of 3 patients with APC*E1317Q. For 1 patient, we show linkage to a specific APC allele. We further show that loss of heterozygosity of the APC gene in tumors from carriers of the APC*E1317Q mutation may involve the mutated allele, not just the wild-type allele, suggesting the APC*E1317Q missense mutation may not be pathologically significant in the development of colorectal tumors.

Contents Vol. 146, 2015

Jacqueline Smith Division of Genetics and Genomics Roslin Institute, Roslin Midlothian EH25 9PS (UK) Tel. (+44) 131 527 4200 Fax (+44) 131 440 0434 E-mail: jacqueline.smith@bbsrc.ac.uk Plant cytogenetics and genomics Andreas Houben Institute of Plant Genetics and Crop Plant, Research (IPK) Corrents-Str. 3 Gatersleben, D–06466 (Germany) Tel. (+1) 785 532 2364; Fax (+1) 785 532 5692 E-mail: houben@ipk-gatersleben.de

The Gene Variant MLH1*D132H is Not Associated with an Increased Risk for Colorectal Adenomas in a Suburban United States Jewish Population

Background: MLH*D132H, a variant of the mismatch repair gene MLH1, was reported linked to an increased risk for colorectal carcinoma in Israeli patients. We evaluated U.S. Jewish patients with adenomas for this gene variant and compared the results to that of three other minor variants. Methods: DNA was screened for the MLH1*D132H variant using standard PCR followed by melting point analysis or by single-stranded conformation polymorphism. Results: Of the 632 patients screened there were three carriers among patients with adenomas and one carrier among those patients with no lesions for an incidence of 0.63% and a relative risk of 0.81 (C.I.=0.08-7.85, p=1.00). Conclusion: We did not detect a significant risk for colorectal adenoma in association with the MLH1*D132H variant. The personal, family history and germ line features of the carriers illustrate the complexity of minor genetic determinants.

Sporadic desmoid tumor in an Ashkenazi patient homozygous for the APC*I1307K gene mutation

Department of Medicine, Saint Barnabas Medical Center, Livingston, New Jersey, USA, Department of Pathology, Saint Barnabas Medical Center, Livingston, New Jersey, USA, Department of Pathology, Saint Barnabas Medical Center, Livingston, New Jersey, USA, Department of Surgery, Saint Barnabas Medical Center, Livingston, New Jerey, USA, Molecular Diagnostics Laboratory, Jewish General Hospital, Montreal, Canada, Division of Medical Genetics, McGill University, Montreal, Canada and Genetic Epidemiology Division, St. James’s University Hospital, Leeds, England, and Cancer Research, UK