Screen smokers who quit 15 or more years ago

Volume 5, Issue 2, 2016


Researchers urge expansion of national lung cancer screening guidelines.

Photograph of Ping Yang, M.D., Ph.D.

Ping Yang, M.D., Ph.D.

Expanding lung cancer screening to include people who quit smoking more than 15 years ago could detect more cases of lung cancer and further reduce associated mortality, according to a study by Mayo Clinic researchers published in the February 2016 issue of the Journal of Thoracic Oncology.

"A decline in smoking rates has been, and continues to be, a critical step to reduce lung cancer risk and deaths," said the study's lead author, Ping Yang, M.D., Ph.D., an epidemiologist with the Mayo Clinic Cancer Center, Rochester, Minnesota. "But it also means that fewer people have benefited from early detection of lung cancer, because more patients don't qualify for low-dose CT scans."

Current lung cancer screening criteria set by the U.S. Preventive Services Task Force (USPSTF) recommend CT screening for adults between the ages of 55 and 80 who have smoked at least one pack a day for 30 years and still smoke, or who have quit smoking for 15 years or less.

In a study published Feb. 24, 2015, in JAMA, Dr. Yang and her colleagues found that two-thirds of patients in the U.S. with newly diagnosed lung cancer would not meet the current USPSTF screening criteria, suggesting a need to adjust the definition of patients at high risk.

In the current study, Dr. Yang and her colleagues set out to identify which specific populations are at risk but are being missed because of the current lung cancer screening criteria. Researchers retrospectively tracked two groups of people with lung cancer: a hospital cohort of 5,988 people referred to Mayo Clinic, and a community cohort of 850 residents of Olmsted County, Minnesota.

The researchers found that patients who quit smoking for 15 to 30 years accounted for the greatest percentage of patients with lung cancer who didn't qualify for lung cancer screening. The newly defined high-risk group constituted 12 percent of the hospital cohort and 17 percent of the community cohort.

"We were surprised to find that the incidence of lung cancer was proportionally higher in this subgroup compared with other subgroups of former cigarette smokers," Dr. Yang said. "The common assumption is that after a person has quit for so many years, the lung cancer rate would be so low that it wouldn't be noticeable. We found that assumption to be wrong. This suggests we need to pay attention to people who quit smoking more than 15 years ago, because they are still at high risk of developing lung cancer."

Equally important, the current study found that expanding the criteria for CT screening would not significantly add to the number of false-positive cases and would save more lives with an acceptable amount of radiation exposure and cost.

Dr. Yang and her colleagues showed that expanding the criteria to include this risk category could add 19 percent more CT examinations for detecting 16 percent more cases of lung cancer. They calculated that this expansion would result in minimal increases in false-positive results (0.6 percent), over diagnosis (0.1 percent) and radiation-related lung cancer deaths (4 percent).

"Lung cancer rates are dropping because smoking is decreasing, but that doesn't mean that our current screening parameters are good enough," Dr. Yang said. "It is understandable, because the relative importance of risk factors changes over time. We need to adjust screening criteria periodically, so we can catch more lung cancers in a timely fashion. Based on our data, which are more recent and come from a well-defined population, I think that we should take action to screen this group, which is at high risk of developing the disease."