Microsatellite stable colorectal cancers in clinically suspected hereditary nonpolyposis colorectal cancer patients without vertical transmission of disease are unlikely to be caused by biallelic germline mutations in MYH.

Microsatellite analysis and immunohistochemistry are commonly used initial screening tests for hereditary nonpolyposis colorectal cancer. However, tumors in roughly one-half of the patients fulfilling the Bethesda guidelines are microsatellite stable. In addition, normal mismatch repair protein expression in these tumors suggests that a defect in the mismatch repair system is unlikely. Because biallelic MYH mutations occur in patients with both high and low numbers of adenomas, we hypothesized that MYH is involved in the tumorigenesis of microsatellite stable colorectal cancers in patients without vertical transmission of disease and who fulfill the Bethesda guidelines. MYH was analyzed in 50 cancer patients and 116 healthy controls by complete genomic DNA sequencing. No biallelic germline mutations were identified. One patient was a heterozygous carrier for the p.G382D missense mutation, and another patient was a heterozygous carrier for the novel missense mutation p.Q484H. We identified six common variants, three in the coding region (p.V22M, p.Q324H, and p.S501F) and three in adjacent intronic regions (c.157+30A>G, c.462+35G>A, and c.1435-40G>C). In summary, biallelic germline mutations of MYH are unlikely to cause colorectal cancer in patients sharing clinical features with hereditary nonpolyposis colorectal cancer families without mismatch repair defect and therefore cannot fill the molecular diagnostic gap in this subgroup of Bethesda-positive patients.

Ten novel MSH2 and MLH1 germline mutations in families with HNPCC.

Hereditary nonpolyposis colorectal cancer (HNPCC) is one of the most common hereditary cancer-susceptibility syndromes. Germline mutations in mismatch repair genes are associated with the clinical phenotype of HNPCC. We report ten novel germline mutations, three in MSH2 and seven in MLH1. All but one mutation have been found in families fulfilling criteria of the Bethesda guidelines; four of them additionally fulfilled the Amsterdam criteria I or II. Eight mutations were considered pathogenic and predictive diagnostics in healthy family members at risk shall be undertaken; these include five frameshift mutations leading to premature stop codons, in MSH2: c.1672delT (p.S558Xfs) and c.2466_2467delTG (p.C822X) and in MLH1: c.1023delG (p.R341Xfs), c.1127_1128dupAT (p.K377Xfs) and c.1310delC (p.P437Xfs); three mutations leading to splice aberrations, in MSH2: c.1661G>C (r.1511_1661del) and in MLH1: c.677+3A>C (r.589_677del) and c.1990-2A>G predicted to result in a splice site defect. The remaining two mutations are unclassified variants with assumed pathogenicity: one missense mutation in the highly conserved ATPase domain of MLH1 (c.122A>G [p.D41G]) and one in-frame insertion of twelve nucleotides in MLH1 (c.2155_2156insATGTGTTCCACA [p.I719delinsNVFHI]). These two mutations were not found in 102 alleles of healthy control individuals. The corresponding tumors from all patients showed a high level of microsatellite instability (MSI-H). Immunohistochemistry (IHC) revealed complete loss of expression of the affected protein in the tumor cells from all but three patients. The tumors from the patients with the mutations c.1127_1128dupAT and c.1990-2A>G showed a reduction of expression of the MLH1-protein, rather than complete loss. In the tumor from the patient with the missense mutation c.122A>G [p.D41G] a normal expression of the proteins coded by MLH1 and MSH2 was noticed.

Occult endometrial cancer and decision making for prophylactic hysterectomy in hereditary nonpolyposis colorectal cancer patients.

BACKGROUND AND OBJECTIVE: Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent form of hereditary colorectal cancer. In addition to the high lifetime risk for colorectal cancer in mutation carriers, there is also a remarkably increased risk for endometrial cancer (EC). METHODS: In this retrospective study, clinical and molecular approach to the individual decision making as to whether or not to perform a prophylactic hysterectomy in a subset of HNPCC patients is discussed. 147 female patients meeting at least one criterion of the Bethesda guidelines were included in this analysis between 1995 and 2003. After clinical and genetic counseling, patients gave informed written consent and microsatellite analysis, immunohistochemistry and sequencing of the mismatch repair genes MLH1, MSH2 and MSH6 was performed. RESULTS: 11 of the analyzed patients had a personal history of EC and had undergone previous hysterectomy at ages 26 to 62 years. Prophylactic hysterectomy with oophorectomy was considered in postmenopausal women meeting the Amsterdam criteria and/or carrying a disease causing mismatch repair gene mutation who were operated on because of diagnosed colorectal cancer in our center for hereditary cancer. This procedure was performed in 4 patients. None of them had shown any symptoms of a gynecologic malignancy. Preoperative gynecological examination showed no evidence for EC or ovarian cancer in these patients. Postoperative histological examination showed EC stage T1b N0 M0 in 2 patients. CONCLUSIONS: Since the efficiency of gynecological surveillance is uncertain, prophylactic hysterectomy could be an option for a subset of HNPCC patients and mutation carriers.