The Association of Clinical Pathologists Molecular Pathology and Diagnostics Group recently issued guidance for RAS testing in colorectal cancer in personalized medicine settings within the United Kingdom and especially within the British National Health Service. The recommendations were included in a Journal of Clinical Pathology article, “RAS testing of colorectal carcinoma—a guidance document from the Association of Clinical Pathologists Molecular Pathology and Diagnostics Group,” and their goal, in part, is to guide anti-epidermal growth factor receptor (EGFR) therapy.
The guidelines state that primary or metastatic tissue can be used for RAS testing, and it can come from biopsy or resection specimen tissue, with resection tissue being preferred if both are available. The article also contains specific advice for laboratorians to use as a guide in handling RAS testing. For example, it says that precision and accuracy of the assay should be analyzed and recorded. “In the context of detection of RAS mutations using qualitative assays, precision refers to how reproducibly the assay can detect the same mutation, whereas accuracy refers to whether or not the assay can detect reference genotypes, whether mutant or wild-type. Precision can therefore be assessed through repeat analysis of the same DNA sample within the same run, between runs and between operators at different times and in different conditions,” the authors wrote. “Accuracy encompasses key aspects of a qualitative test (including its sensitivity and specificity), and is best assessed using clinical samples which have been genotyped either with a different, previously validated assay in the same laboratory or by the same assay in a different laboratory.”
Additionally, sensitivity of this type of testing is addressed in the new report. “The number of clinical specimens required for validation depends on the statistical power required in each laboratory and for each test. For example, a validation performed with 100% experimental sensitivity (i.e., all results are correct) using only 30 specimens will lead to a statistical chance of a false negative of 10%, and therefore the sensitivity of the assay is predicted to be 90%,” the article states. “However, the same experimental sensitivity using 300 specimens predicts for a test sensitivity of 99%.” The type of validation chosen should be based on the intention of the test, as well as the clinical setting, although “current literature lacks any firm indication of the optimal level of validation for RAS testing of CRC,” according to the article.
Read the guidance document online.