Death rates for the most common type of lung cancer have fallen significantly in the United States in recent years, an improvement resulting in large part from new targeted treatments, according to a study by the National Cancer Institute.

The study, published Wednesday in the New England Journal of Medicine, said death rates for men with non-small-cell lung cancer declined 6.3 percent per year from 2013 to 2016. The number of cases — the incidence — also decreased but at a much slower rate. That meant, the researchers said, that a reduction in smoking, which reduces the risk of lung cancer, was not the only reason for the decline in death rates. People who developed cancer also were benefiting from better treatments.

Lung cancer remains the leading cause of cancer death in the United States. The American Cancer Society estimates that almost 230,000 new cases of lung cancer will be diagnosed in the United States this year, and 135,720 people will die of the disease.

The decline in yearly death rates was twice as large between 2013 and 2016 as for the seven years before that. Two-year survival increased from 26 percent for men diagnosed with the disease in 2001 to 35 percent for those diagnosed in 2014. Similar improvements were seen among women, the researchers said.

The trend “correlates with the [Food and Drug Administration] approval of several targeted therapies for this cancer in recent years,” Douglas R. Lowy, NCI deputy director and co-author of the study released Wednesday, said in a statement.

In recent years, new treatments for non-small-cell lung cancer have emerged that target genetic mutations or alterations, including those commonly called EGFR or ALK. Doctors also started routine testing of patients to determine the best treatments.

The study focused on non-small-cell lung cancer, which accounts for 76 percent of lung cancer cases in the United States and small-cell lung cancer, which accounts for 13 percent. The researchers found that death rates from small-cell lung cancer also decreased in recent years, but at about the same pace as decreases in new cases. That suggests that smoking reductions are responsible for those decreases in mortality rates. Scientists have had much more trouble finding successful treatments for small-cell lung cancer than for non-small-cell lung cancer.

“The key takeaway,” said Nadia Howlader, the researcher who led the study, “is that lung cancer is not one disease, it’s a collection of many diseases. It’s very important for patients to talk to their doctors about what kind of lung cancer they have.”

The researchers explored whether lung cancer screening — in which a patient undergoes a low-dose CT scan to detect possible malignancies in the lung — helped fuel the decreases in non-small-cell lung cancer death rates. But they concluded that screening rates, which remained low and stable, do not explain the mortality declines.

Roy Herbst, a lung cancer expert at Yale Cancer Center who was not involved in the study, said the data support what he has witnessed in his practice.

“We are making amazing progress in this leading cause of death,” Herbst said. “But it’s not nearly good enough. We still have a lot of work to do.”

Herbst said doctors need to encourage patients to get genetic testing. “Only about 70 percent or so of patients get the profile done,” he said. The goal, he added, is to increase the use of targeted therapies in patients who are at earlier stages of their disease.

He said he expects further improvement in death rates once they begin to reflect the impact of widespread use of immunotherapy for certain kinds of lung cancer. The arrival of immunotherapy, which is designed to marshal the body’s immune system against cancer, is not reflected in the new study’s statistics, the researchers said.

One drawback with targeted therapies is that patients’ malignancies often become resistant to those therapies, requiring a switch to another targeted medication or another type of treatment.

The targeted therapies approved in the past several years include Tagrisso, also known by the generic name osimertinib, and Xalkori, which is also known as crizotinib. Other targeted therapies also have been approved.

The death rate from cancer in the United States declined by 29 percent from 1991 to 2017, including a 2.2 percent drop from 2016 to 2017, the largest single-year drop ever recorded, the American Cancer Society reported this year.

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