CHICAGO: New cancer drugs that target genetic mutations regardless of where the tumor is growing should expand the practice of testing patients for such glitches, oncology experts say. Such 'tumor-agnostic' drugs from companies including Merck & Co and Loxo Oncology may help overcome misgivings by health insurers, who have balked at covering large-scale tests looking for genetic mutations in tumors, and quell concerns of some top cancer doctors who question whether enough patients benefit from such tests. Last month, Merck's immunotherapy Keytruda became the first cancer treatment ever to win US approval based on whether the tumor carried a specific genetic glitch, irrespective of the tumor's location. More recently, Loxo showed that its drug larotrectinib helped shrink tumors in 76 percent of patients with a wide variety of advanced cancers who carried a specific genetic defect. The surprising results suggested a benefit of testing many patients for the same defects. 'Insurance companies had an easy out' before the Merck approval and Loxo data, said Dr. David Hyman of Memorial Sloan Kettering Cancer Center in New York. Hyman presented the Loxo results at the American Society of Clinical Oncology annual meeting last weekend. 'They have asked, 'Show me the evidence this helps patients.' It didn't exist,' he said. 'Now we have these data.' A second company, Ignyta Inc, has developed a drug that targets the same genetic glitch as Loxo’s larotrectinib, and both treatments are under expedited review by US regulators. At the US Food and Drug Administration, cancer chief Dr. Richard Pazdur said he is 'very supportive' of the tumor-agnostic approach and believes more such approvals are likely. 'What we're seeing is the result of a lot of work that has been done to determine how these drugs work,' Pazdur told Reuters. Such evidence may begin to sway insurers, but it's not clear how quickly. Aetna Inc said it is studying the Keytruda approval and will base its decision about testing based on the medical evidence and whether the treatments improve quality, reduce waste and provide members with access to affordable care. Dr. Jeffrey Hankoff of Cigna Inc said the company 'generally does not cover multi-gene panels' unless they are recommended by the National Comprehensive Cancer Network, a nonprofit group that sets cancer treatment guidelines. 'Ultimately, it's a matter of having actionable information from genetic testing that is based on evidence, not on conjecture,' Hankoff said. ENTHUSIASM WANING In 2001, Novartis drug Gleevec transformed the treatment of chronic myelogenous leukemia (CML) from a fatal blood cancer to a treatable condition for most patients. The drug takes aim at a single genetic defect, raising hopes for a new age of targeted drugs that work better and more safely than traditional chemotherapy. Since then, gene sequencing has become exponentially faster and cheaper. Five years ago, companies such as Foundation Medicine introduced genetic profiling tests that look for a range of cancer-causing genes to match patients to a handful of targeted drugs for lung, skin and breast cancer or to clinical trials testing new agents. Many doctors have embraced the practice, hoping to find a treatment for patients with advanced cancers who were out of options. But insurers have been slow to pay for the tests, which cost $1,000 to $5,000 and can result in the off-label use of targeted drugs with no evidence that they work. In late 2015, a randomized trial showed such testing yielded no survival advantage compared with conventional therapy. The finding triggered a fierce debate in medical journals, with some experts questioning whether hype has gotten ahead of the science. 'There are patients that benefit, but it's very much a minority of the patients,' said Dr. Scott Kopetz, a colorectal cancer specialist at the University of Texas MD Anderson Cancer Center. Hyman argues that the Keytruda approval based on a single genetic defect 'changed the field overnight' and will gain momentum with the likely approval of larotrectinib, which targets a defect called TRK fusions. Experts estimate up to 1 percent of all cancer patients have TRK fusions. Dr. John Heymach, an oncologist from MD Anderson Cancer Center in Texas who was not involved in the Loxo study, said it underlines 'the importance of expanding what we're looking for.'