This may be because Lynch Syndrome cancers commonly arise in colorectal adenomas already bearing the APC mutation, whereas sporadic microsatellite unstable colorectal cancers arise from serrated polyps typically lacking APC mutation, decreasing the selection pressure on other WNT signaling related loci in Lynch syndrome.
Two familial forms of colorectal cancer (CRC), Lynch syndrome (LS) and familial adenomatous polyposis (FAP), are caused by rare mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2) and the genes APC and MUTYH, respectively.
Recently, we reported that in difficult cases finding pathogenic APC variants supports a colonic origin.In this case report we describe the clinical history of a female patient suspected for Lynch syndrome.
We asked whether in Lynch syndrome biallelic inactivation of MMR genes occurred at a similar frequency to that of APC gene, and whether MMR inactivation resulted in detectable lesions within the intestinal mucosa.
It is well known that germ line mutations in the cis-element of tumor suppressor genes such as mismatch repair (MMR) genes, the adenomatous polyposis coli (APC) gene and the E-cadherin (CDH1) gene are involved in Lynch syndrome, familial adenomatous polyposis and hereditary diffuse gastric cancer, respectively.
However, ZEB1 is not expressed in the epithelium of hereditary forms of CRCs that carry wild-type APC and where β-catenin is excluded from the nucleus (Lynch syndrome).
We found a significant difference in cytoplasmic APC expression frequency between sporadic MSS (52%) and HNPCC tumors (78%), whereas no difference was detected between MSI-H and MSS or HNPCC tumors.
The genes responsible for each disease were identified almost two decades ago -APC for FAP and the MMR genes for HNPCC - and a large number of germline variations have been identified in these genes in hereditary cancer patients.
Analyses included completion of APC gene exon 16 sequencing, analysis for APC gene copy number variations (deletions or duplications), MUTYH gene sequencing, and microsatellite instability in CRC patients fulfilling "Bethesda" (laboratory investigation) criteria for Lynch syndrome.
There are two major hereditary colorectal cancer syndromes: Adenomatous Polyposis, secondary to APC germline alterations (FAP, Familial Adenomatous Polyposis) or secondary to MUTYH germline alterations (MAP, MUTYH associated Polyposis), and Lynch syndrome, associated with germline mutations in mismatch repair genes (MLH1, MSH2, MSH6 and PMS2).
Mutations in DNA mismatch repair genes are associated with high risk of digestive malignancies [hereditary non-polyposis colorectal cancer (HNPCC); Lynch syndrome]; mutations of APC and MYH are associated with classic and attenuated familial adenomatous polyposis (FAP).
Furthermore, five markers (BAT25, BAT26, D2S123, APC, and D17S250) of the Bethesda consensus panel for detection of colorectal cancer within the hereditary non-polyposis colon cancer syndrome (HNPCC) were analyzed.
In addition, the rate of the I1307KAPC missense mutation and the two predominant Jewish mutations in hMSH2, A636P, and 324delCA, associated with hereditary nonpolyposis colon cancer (HNPCC), were determined.
Molecular changes (K-ras and beta-catenin mutations, chromosome 18q allele loss (LOH), APC LOH, microsatellite instability (MSI), and expression of beta-catenin and p53) were examined in four series of CRC patients with proven or probable hereditary disease: hereditary non-polyposis colon cancer (HNPCC); MYH associated polyposis (MAP); multiple (>5) colorectal adenomas without familial adenomatous polyposis (FAP); and other families/cases referred to family cancer clinics (FCC series).
Complete or partial gene deletions were identified in seven cases for hMSH2 (5.7% of mutation-negative HNPCC; 4.3% of all HNPCC), no cases for hMLH1 and six cases for APC (25% of mutation negative FAP; 8% of all FAP).
This article traces the historical aspects of hereditary cancer dealing with identification and ultimate molecular genetic confirmation of commonly occurring cancers, particularly of the colon in the case of familial adenomatous polyposis and its attenuated form, both due to the APC germline mutation; the Lynch syndrome due to mutations in mismatch repair genes, the most common of which were found to be MSH2, MLH1, and MSH6 germline mutations; the hereditary breast-ovarian cancer syndrome with BRCA1 and BRCA2 germline mutations; the Li-Fraumeni (SBLA) syndrome due to the p53 mutation; and the familial atypical multiple mole melanoma in association with pancreatic cancer due to the CDKN2A (p16) germline mutation.
Many cases of HNPCC are due to germline mutations in DNA mismatch repair genes, leading to the tumor phenotype of microsatellite instability (MSI), and most cases of FAP are caused by germline APC mutations.
Our previous study detected a low frequency of APC gene mutation (21%) in colorectal tumors from HNPCC patients, in contrast to a high frequency of APC gene alteration (>70%) in non-HNPCC tumors.
The discipline of molecular genetics has identified germline mutations that include APC in familial adenomatous polyposis (FAP) and mutator genes, namely MSH2, MLH1, PMS1, and PMS2 in hereditary nonpolyposis colorectal cancer (HNPCC).
In colorectal cancer such loci include the familial adenomatous polyposis (APC) gene and the hereditary nonpolyposis colorectal cancer (DNA mismatch repair) genes.
APC, p53, and K-ras-2 mutations and loss of heterozygosity of tumor-suppressor genes were significantly less frequent (P = 0.03 to 0.0006) but transforming growth factor beta type II receptor mutation was significantly more frequent (P = 0.000001) in HNPCC than in non-HNPCC.