Background and aims: Mutations in BRAF have been linked with colorectal cancers (CRC) showing high level microsatellite instability (MSI-H). However, the distribution of BRAF mutations in MSI-H cancers remains to be clarified with respect to precursor lesions and the CpG island methylator phenotype (CIMP). Methods: Forty three hyperplastic polyps (HP), nine mixed polyps (MP), five serrated adenomas (SA), 28 conventional adenomas (AD), 18 hereditary non-polyposis colorectal cancers (HNPCC), and 127 sporadic CRC (46 MSI-H and 81 non-MSI-H) were collected from patients undergoing colectomy for either CRC or hyperplastic polyposis. Twenty five of 57 serrated lesions were derived from four patients with hyperplastic polyposis. HP were further subdivided according to recently documented morphological criteria into 27 classical HP and 16 variant lesions described as ''sessile serrated adenoma'' (SSA). All tumours were screened for BRAF activating mutations. Results: The BRAF mutation was more frequent in SSA (75%) and MP (89%) than in classical HP (19%), SA (20%), and AD (0%) (p,0.0001), and also in sporadic MSI-H cancers (76%) compared with HNPCC (0%) and sporadic non-MSI-H cancers (9%) (p,0.0001). The BRAF mutation was identified more often in CIMPhigh serrated polyps (72%) and CIMP-high CRC (77%) than in CIMP-low (30%) and CIMP-negative (13%) polyps (p = 0.002) as well as CIMP-low (18%) and CIMP-negative (0%) CRC (p,0.0001). Conclusions: The BRAF mutation was frequently seen in SSA and in sporadic MSI-H CRC, both of which were associated with DNA methylation. Sporadic MSI-H cancers may originate in SSA and not adenomas, and BRAF mutation and DNA methylation are early events in this ''serrated'' pathway.

Lynch syndrome, also known as hereditary nonpolyposis colon cancer syndrome (1), is a rare, autosomal, dominantly inherited syndrome caused by germline mutations in DNA mismatch repair genes, which confer substantial risks for cancers of the colorectum and endometrium and increased risks for cancers of the stomach, small intestine, hepatobiliary system, kidney, ureter, ovary, and sebaceous tumors (2,3). Mutations in the mismatch repair genes, MLH1 and MSH2, account for 70%-80% of all Lynch syndrome colorectal cancers (ie, colorectal cancers occurring in people with germline DNA mismatch repair gene mutations) (4-7).Mutations in MSH6 account for 10%-20% of Lynch syndrome colorectal cancers and 0.4% of all colorectal cancers (4-7), with the greater proportion of colorectal cancer diagnosed at a younger age (4,6). The prevalence of MSH6 mutations in women with endometrial cancer who were not selected for family history is less well established with estimates ranging from 1.0% to 3.8% (8-12).Few studies have attempted to estimate the age-specific cumulative cancer risk for carriers of germline mutations in MSH6 (penetrance) (13-18), so information on the consequences of such mutations remains uncertain. Most of these studies (13-16) have analyzed data from families that were ascertained because of a strong family history of cancers related to Lynch syndrome, or preferentially mutation-tested individuals with colorectal cancer over individuals without colorectal cancer, and appear not to have correctly taken into account the ascertainment when deriving their penetrance estimates. Recruiting families from family cancer clinics will result in oversampling of family members who have been diagnosed with colorectal or other cancers, and such recruitment has been shown to result in inflated estimates of cancer risks

Purpose Clinicopathologic data from a population-based endometrial cancer cohort, unselected for age or family history, were analyzed to determine the optimal scheme for identification of patients with germline mismatch repair (MMR) gene mutations. Patients and Methods Endometrial cancers from 702 patients recruited into the Australian National Endometrial Cancer Study (ANECS) were tested for MMR protein expression using immunohistochemistry (IHC) and for MLH1 gene promoter methylation in MLH1-deficient cases. MMR mutation testing was performed on germline DNA of patients with MMR-protein deficient tumors. Prediction of germline mutation status was compared for combinations of tumor characteristics, age at diagnosis, and various clinical criteria (Amsterdam, Bethesda, Society of Gynecologic Oncology, ANECS). Results Tumor MMR-protein deficiency was detected in 170 (24%) of 702 cases. Germline testing of 158 MMR-deficient cases identified 22 truncating mutations (3% of all cases) and four unclassified variants. Tumor MLH1 methylation was detected in 99 (89%) of 111 cases demonstrating MLH1/PMS2 IHC loss; all were germline MLH1 mutation negative. A combination of MMR IHC plus MLH1 methylation testing in women younger than 60 years of age at diagnosis provided the highest positive predictive value for the identification of mutation carriers at 46% versus ≤ 41% for any other criteria considered. Conclusion Population-level identification of patients with MMR mutation-positive endometrial cancer is optimized by stepwise testing for tumor MMR IHC loss in patients younger than 60 years, tumor MLH1 methylation in individuals with MLH1 IHC loss, and germline mutations in patients exhibiting loss of MSH6, MSH2, or PMS2 or loss of MLH1/PMS2 with absence of MLH1 methylation.

The total number of genes and MINTs methylated in HNPCC was lower than in MSI-H colorectal tumours. No HNPCC tumour showed evidence of widespread promoter hypermethylation or BRAF mutation suggesting this feature could be used as a discriminator between familial and sporadic cases.