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Current Cancer Genetic Testing Guidelines May Miss Actionable Heritable Mutations

NEW YORK (GenomeWeb) – Current genetic testing guidelines for cancer patients, which are primarily based on family history, may miss actionable, heritable mutations, according to a new study published today in the Journal of the American Medical Association.

Researchers at Memorial Sloan Kettering Cancer Center analyzed 76 cancer predisposition genes in 1,040 patients with advanced cancer whose oncologists referred them for germline testing, finding actionable heritable mutations in 182, or nearly 18 percent. Of those patients, almost 55 percent, or 101, would have been missed had current standard guidelines been followed for testing.

Kenneth Offit, chief of clinical genetic services and the Robert and Kate Niehaus Chair in inherited cancer at MSKCC, said in a statement that it was "surprising" to find such a a "large number of individuals with inherited mutations who would not have been aware of the risk to their families" without testing. "At the time of a diagnosis of advanced cancer we have a vital opportunity, through comprehensive genetic testing, to set the stage for precision prevention for patients' families," he added.

The study adds to a growing body of evidence that more comprehensive germline testing of cancer patients can identify actionable inherited mutations that may have implications not only for the patient's own treatment, but family members as well.

For instance, MSKCC researchers reported last year in JAMA Oncology that for patients in whom it identified germline mutations, around half had mutations not typically associated with their cancer type.

Genetic testing firm Counsyl also reported last year following a three-month program in which it offered free inherited cancer screening to women in the San Francisco Bay Area that nearly half of the women who were found to have inherited mutations did not meet the National Comprehensive Cancer Network's guidelines for screening.

In the study published today, the MSKCC team reported that they tested more than 10,000 patients who had advanced cancer with the center's MSK-IMPACT test, a 410-gene next-generation sequencing panel, between January 2014 and May 2016. Oncologists subsequently referred 1,040 of those patients for germline testing in 76 cancer predisposition genes.

Of the 1,040 patients, the most common diagnoses were prostate, renal, pancreatic, breast, and colon cancers. Just over 17 percent, or 182 patients, had actionable germline mutations, including 149 patients who had moderate- to high-penetrance variants. More than half of the patients with actionable germline mutations, 101, would not have been referred for testing based on clinical guidelines, including 65 who had moderate- to high-penetrance mutations.

As a result of the findings in inherited cancer genes, treatment was changed or physicians began discussing a potential change in treatment in 38 patients. In addition, the family members of 13 patients were subsequently tested for the cancer risk mutations identified.

In a corresponding editorial also published today in JAMA, Eliezer Van Allen, a clinical computational oncologist at the Dana-Farber Cancer Institute, wrote that the results "raise multiple provocative questions for the precision cancer medicine field." The study highlights the challenges both of determining the appropriate test, as well as the appropriate patients to test, Van Allen wrote.

In addition, further study of germline testing in cancer patients would require investment in "pretest counseling, interpretation, and downstream clinical management." Variants of unknown significance, of which the MSKCC team reported finding on average two per patient, will pose additional hurdles. Van Allen noted: "These ambiguous findings may result in higher rates of emotional stress, unnecessary testing, and overtreatment in an already encumbered advanced cancer population."

Nonetheless, Van Allen wrote that the clinical utility of germline analysis in cancer patients "should be tested in prospective clinical studies" and "compared to standard-of-care guideline-driven genetics on patient outcomes."