The new study compared tumor cells from 178 squamous cell lung cancer patients with the patients’ normal cells. More than 60 percent of the tumors had alterations in genes used to make enzymes that are particularly vulnerable to the new crop of cancer drugs. Many of the drugs are already available or are being tested on other cancers.

These enzymes function like on-off switches for cell growth, said Dr. Roy S. Herbst of Yale Cancer Center, who was not an author of the new study. When they are mutated, the switches are stuck in an on position. About a dozen companies, Dr. Herbst added, have drugs that block these mutated enzymes.

Yet even though the squamous cell cancers analyzed in the study often had mutations in genes for these enzymes, the genes and the mutations were different in different patients.

“Unfortunately, what the Cancer Genome Atlas has revealed is that everyone’s cancer could be very different,” said Dr. William Pao, a lung cancer researcher at the Vanderbilt-Ingram Cancer Center in Nashville and an author of the new paper. “The field is really moving toward personalized medicine.”

The study also found a real surprise, Dr. Meyerson said, something that had not previously been seen in any cancer. About 3 percent of the tumors had a gene mutation that might allow them to evade the immune system. By coincidence, an experimental drug that unleashes the immune system was recently tested in lung cancer patients. Some of those who did not respond might have the mutation, he said.

Now the challenge is to put the findings to clinical use.

First, researchers have to establish that the mutations in question actually are essential to the tumors’ growth, said Dr. Bruce Evan Johnson, a lung cancer researcher at Dana-Farber and an author of the new paper. There are several steps: show that if the mutated gene is added to normal cells, they turn into cancerous cells; show that if the mutated gene is added to mice, they develop squamous cell lung cancer; and show that if the gene is turned off — with a drug, for example — in cells grown in a laboratory, the cells die.

Then come drug tests in patients. But if only a small percentage of patients have each of the mutations, that poses a problem. Ordinarily a few medical centers would enroll patients with a particular type of cancer, like squamous cell. But if, instead, squamous cell patients are subdivided according to their gene mutations, there would be too few for a drug test within a single institution or even several.