EXECUTIVE SUMMARYAn original evidence review examined screening and diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) and the subsequent outcomes in a population of newly diagnosed cases of colorectal cancer (CRC). This supplementary evidence review focuses on five issues of further interest to the Evaluation of Genomic Applications in Practice and Prevention (EGAPP) Working Group (EWG), as summarized below.
Clarifying how to define the clinical disorder-Lynchsyndrome. In this supplementary review, Lynch syndrome refers to individuals with a predisposition to CRC and certain other malignancies as a result of a germline mismatch repair (MMR) gene mutation-including those with an existing cancer and those who have not yet developed cancer. This definition allows planned analyses of clinical validity and utility to be more straightforward. Several recent editorials and publications recommend that the ambiguous term HNPCC be abandoned and that this clarified definition of Lynch syndrome should be used instead.
Removing family history from consideration as a preliminary test.A previous evidence review showed that screening performance of both the Amsterdam and the Bethesda criteria to identify individuals with Lynch syndrome were highly heterogeneous, possibly due to differences among the populations tested. In a general population, Amsterdam criteria are associated with relatively low sensitivity (28 -45%), but high specificity (99%), whereas Bethesda criteria are associated with higher sensitivity (73-91%), but at the cost of lower specificity (82-77%). Neither provides the necessary high sensitivity/specificity in a reliable and consistent manner. There are also gaps in knowledge relating to the time required to collect family history, the consistency with which it is collected, and the accuracy of the information. Inadequate evidence was available to determine the distribution of mutations in the MMR genes, but the limited data suggest 32% will be in MLH1, 38% in MSH2, 14% in MSH6, and 15% in PMS2. Adequate evidence was available to estimate sensitivity (69%) and specificity (point estimate of 100%) for identifying Lynch syndrome using a specific mutation in the BRAF gene among those with absent IHC staining for MLH1. An alternative to BRAF mutation testing might be direct testing of MLH1 methylation status, but this was not evaluated.
Benefits and harms to probands and relatives with Lynchsyndrome. Between 2 and 12 first-degree relatives of probands (newly diagnosed CRC cases with Lynch syndrome, or index cases) can be contacted, based on resources and methodology. There was adequate evidence to document uptake of counseling among these firstdegree relatives who were contacted (52%) and subsequently targeted for MMR gene mutation testing (95% however, may be subject to family history bias. The U.S. Multisociety Task Force on Colorectal Cancer recommends colonoscopy every 1 or 2 years for first-degree relatives of individuals diagnosed with Lynch syndrome, and uptake among this group is about 80%. Th...