4113 Background: The single most common cause of hereditary colorectal cancer is the Lynch syndrome, which is associated with deficiency of the mismatch repair genes MLH1, MSH2, or MSH6. Most MLH1 negative tumors are sporadic in origin, and they can be identified if harbouring a BRAF V600E mutation or hypermethylation of the MLH1 promoter. If Lynch syndrome is detected in a patient and its family, screening can prevent death from new colorectal cancer. A family history should always be obtained, but in small families or patients with de-novo mutations and mutations with late or low penetrance, this is not sufficient. The aim of this study was to validate our previously suggested clinically applicable strategy based on molecular characteristics for identifying which patients to refer for genetic counselling. Methods: The strategy was validated in an unselected cohort of 287 colorectal cancer patients. All tumors was tested for MLH1, MSH2, and MSH6 with immunohistochemistry. DNA from MLH1 negative tumors was sequenced for BRAF mutations. If wild-type, MLH1 promoter was analyzed with methylation specific multiplex ligation-dependent probe amplification (MLPA). MLH1 negative tumors were considered sporadic if BRAF V600E mutation or MLH1 promoter hypermethylation was found. A follow up was done on patients with MSH2 or MSH6 negative tumors and MLH1 negative cases not shown to be sporadic. Results: Most tumors, 251 (88%), stained positive for all three proteins. Six (2%) had negative MSH2 and one (<1%) isolated loss of MSH6. MLH1 was negative in 29 cases (10%). DNA quality allowed BRAF analysis in 27 of these with 14 mutations and 13 wild-type. DNA quality allowed MLPA in four of the 13 BRAF wild-type, and all four were methylated. Subsequently, Lynch syndrome could not be ruled out in 18 patients. A follow-up at 8–10 years revealed four definite Lynch syndrome and four highly suspicious. Conclusions: An easy and clinically applicable step-wise approach with immunohistochemistry (100%), BRAF sequencing (10%), and methylation analysis (5%) identified several patients with hereditary cancer. The family history should be supplemented with a molecular screening for whom to send for genetic counselling. No significant financial relationships to disclose.
Clinicopathological Significance of BRAF V600E Mutation in Egyptian Colorectal Cancer Patients
