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Predicting Colorectal Cancer Risk
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Prediction models that incorporate certain personal and family medical history characteristics can help identify high-risk patients who are likely to have a gene mutation associated with a type of colorectal cancer, according to two studies in the September 27 issue of JAMA.

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Lynch syndrome (also called hereditary nonpolyposis colorectal cancer) is the most common hereditary colorectal cancer syndrome in Western countries, accounting for 2 percent to 5 percent of all colorectal cancers (CRCs). Lynch syndrome is primarily associated with mutations in the MLH1 and MSH2 genes. In hereditary breast-ovarian cancer syndrome, multiple models have been developed to predict mutations in the BRCA1 and BRCA2 genes, and these models are widely implemented by health care professionals as they assess their patients’ genetic risk. For Lynch syndrome, the relative importance of specific aspects of personal and family medical history remains unclear.

Judith Balmana, M.D., formerly of the Dana-Farber Cancer Institute, Boston, and colleagues obtained data from 1,914 individuals undergoing genetic testing of MLH1 and MSH2 and developed a clinical model, the PREMM1,2 (Prediction of Mutations in MLH1 and MSH2) to predict the presence of mutations in the MLH1 and MSH2 genes based on personal and family medical history. A model was developed in an initial group of 898 individuals and subsequently validated in 1,016 patients.

Overall, 14.5 percent (130/898) of the study individuals were found to have mutations: 6.5 percent had mutations in MLH1 and 8.0 percent had mutations in MSH2. In the validation cohort, the overall prevalence of mutations was 15.3 percent. Mutations were particularly prevalent among probands (a patient who is the initial member of a family to come under study) with 2 or more separate CRCs, endometrial cancer, other Lynch syndrome–associated cancers, and multiple diagnoses. The prevalence of mutations in the probands increased with increasing numbers of first-degree relatives with CRC or endometrial cancer. Probands with mutations had a younger average age at CRC diagnosis than those who did not have mutations, and the age at diagnosis of CRC and endometrial cancer was also younger among the relatives of probands with mutations.

“How these risks are translated into clinical decision making depends on a variety of factors, including the availability of comprehensive genetic testing services (sequencing and large rearrangement analysis), the timelines of testing information for clinical management decisions, insurance coverage for testing, and the availability of tissue for analysis. Based on the risk estimate generated from the model and the above factors, a clinician may choose whether genetic evaluation should be pursued, as well as the approach to testing …” the authors write.

“Our prediction rule includes specific and discrete variables and does not rely on complex combinations of diagnoses across generations. The PREMM1,2 model has been externally validated and is available as a user-friendly Web-based model to provide clinicians with an objective tool to estimate the likelihood of finding mutations in the MLH1 and MSH2 genes and to help guide the strategy for molecular evaluation,” the researchers conclude.

JAMA. 2006;296:1469-1478

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