Doctors and hospitals love to talk about the cancer patients they’ve saved, and reporters love to write about them. But deaths still vastly outnumber the rare successes. “There are very few instances in which we can look at a genomic test and pick a drug off the shelf and say, ‘That will work,’” said Dr. Nikhil Wagle, a cancer specialist at Dana-Farber Cancer Institute in Boston who helped develop precision-medicine tests. “That’s our goal in the long run, but in 2018 we’re not there yet.” There has been real progress, of course. Testing for genetic mutations has become standard in lung cancer, melanoma and a handful of other tumor types. But the number of people with advanced cancer eligible for these approaches is just 8 percent to 15 percent, experts estimate. And these targeted therapies help about half of patients who try them, said Dr. Vinay Prasad, an associate professor at Oregon Health and Science University. Some experts, like Dr. David Hyman of Memorial Sloan Kettering Cancer Center in New York, say that such testing should be available to everyone with advanced cancer, because no one can predict which patients will have results that make them eligible for beneficial treatment. When patients respond to these drugs, they tend to do very well, and some survive much longer than expected.