"With little fanfare the Food and Drug Administration did something this week that its never done before The agency approved a single prescription drug pembrolizumab marketed by Merck as Keytruda for treatment of solid tumors in any organ so long as the malignancy bears a specific genetic signature. In the fastmoving field of cancer treatment the FDAs announcement  https an important milestone close to two decades in the making. Increasingly cancer will no longer be identified categorized and treated by the organ it inhabits or in which it first gained its foothold. In a shift that is already underway cancers will be known by  and treated for  the common genetic mutations that nurture and sustain them. In clinical trial evidence cited by the FDA this week pembrolizumab induced complete or partial tumor shrinkage in about  of patients with one of  endstage malignancies. And for  of those patients that response lasted six months or more. A trial reported earlier this year found that in  of  advanced cancer patients pembrolizumab stopped or reversed the progression of cancer and  patients were still alive a year after starting the drug. All of those subjects of course had cancers with the genetic mutation that pembrolizumab is designed to target. In the treatment of patients with metastatic cancers that have failed all other treatments that record of success constitutes a home run said Dr. Bert Vogelstein of Johns Hopkins Universitys Kimmel Cancer Center. Vogelsteins  research laid the groundwork for the discovery of pembrolizumabs broad cancerfighting powers. With the FDAs announcement drugs like pembrolizumab have also begun to change the way that physicians patients and government regulators think of cancer. No longer will they see all cancers of the lung breast colon brain liver pancreas and prostate as distinct from one another. Instead they will look for the common genetic mutations that give rise to cancers no matter where theyre found. And theyll treat those cancers with a drug that uses that common signature as a homing beacon either for the immune system or for targeted cancer drugs to attack. Its a key principle of whats called precision medicine  the idea that cancer therapies should zero in on a tumors specific molecular fingerprint and not as most chemotherapies do harm healthy cells in the process of attacking malignant ones. In the cancers pembrolizumab treats the mutations occur in the complex of genes that govern DNA repair. Deficiencies in the DNAs mismatch repair system generate mutant proteins on the surface of cancer cells and pembrolizumab trains the immune system to attack those targets. The mutations that make pembrolizumab effective had already been found in melanoma nonsmallcell lung cancer head and neck cancer and Hodgkins lymphoma and the FDA had already approved the drug for those cancers before this week. But this weeks FDA approval goes further It makes clear that the drugs molecular targets are also common in colorectal endometrial and gastrointestinal cancers and less frequently present in cancers of the breast prostate bladder and thyroid gland. All told scientists believe about  of advanced cancers bear the genetic signature that would make them treatable by Keytruda. The appearance of such a cancer workhorse will bring about profound changes on the cancer landscape  not just for patients but for researchers and drug regulators as well. Organizations representing say people with pancreatic cancer will make common cause with groups that advocate for colorectal cancer patients. In cancer centers specialists in say melanoma will start in fact have already started treating patients with a range of other cancers. When drug companies and their academic partners set out to test the effectiveness of a prospective cancer drug theyll have to recruit trial subjects using a new and much less obvious criterion than theyve used in the past the genetic signatures their tumors bear. Even before the FDAs announcement this week all these processes were underway. The FDAs decision recognizes that fact said Dr. Svetomir Markovic an immunologist at the Mayo Clinic in Rochester Minn. who specializes in treating melanoma. But the decision also puts cancer physicians  as well as insurers who will be called on to pay Keytrudas peryear price tag  on notice that a new era is at hand said Markovic. The field of cancer medicine is changing at lightning speed he said. Physicians are having a hard time keeping up and I can only imagine that people who are regulating it are doing the same he added. But this decision by the FDA is really wonderful It has made it easier for us to secure treatment for our patients who may have run out of options that may help. Two other immunotherapy drugs have been approved for cancer treatment  nivolumab marketed as Opdivo and ipilimumab Yervoy  but neither has been shown to treat cancers across such a broad spectrum. Several other immunotherapy drugs are in early trials and could yet prove to be the sort of workhorse that pembrolizumab appears to be. In many ways were at the end of the beginning of immunotherapy Theres clear benefit but its still a minority of patients that get longterm benefit said Markovic of the Mayo Institute. We will get better at this. Markovic suggested that the newly recognized powers of pembrolizumab as well as the FDAs new openness to cancer drugs that blur traditional distinctions could prompt drug companies physicians and patient groups to take a second look at some abandoned cancer drugs. With a clearer idea of which patients they might help and a willingness to design and conduct innovative clinical trials some failures may look more promising he said. We just needed to take the first step in showing that this longbelieved theory  that the immune system can kill cancer  is true Markovic added. It indeed can."