Expanding lung cancer screening for ex-smokers
27 JANUARY 2016
Expanding lung cancer screening to include people who quit smoking more than 15 years ago could detect more cases and further reduce associated mortality, according to a study by Mayo Clinic researchers.
“A decline in smoking rates has been, and continues to be, a critical step to reduce lung cancer risk and deaths,” says the study’s lead author Dr Ping Yang, an epidemiologist at Mayo Clinic Cancer Centre. “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.”
The current lung cancer screening criteria set by the US Preventive Services Task Force (USPSTF) recommends CT screening for adults between the ages of 55 and 80 who have smoked at least one pack a day for 30 years and are still smoking, or have quit within 15 years.
In the current study, Yang and her colleagues set out to identify which specific populations of individuals are at risk, but are being missed by the current lung cancer screening criteria. Researchers retrospectively tracked two groups of people with lung cancer: a hospital cohort made up of 5,988 individuals referred to Mayo Clinic and a community cohort consisting of 850 residents of Olmsted County, Minnesota.
They found that, compared to other risk categories, patients who quit smoking for 15 to 30 years accounted for the greatest percentage of patients with lung cancer who didn’t qualify for screening. The newly defined high-risk group constituted 12% of the hospital cohort and 17% of the community cohort.
“We were surprised to find that the incidence of lung cancer was proportionally higher in this subgroup, compared to other subgroups of former cigarette smokers,” says Yang. “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 for 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.
Yang and her colleagues showed that expanding the criteria to include this risk category could add 19% more CT examinations for detecting 16% more cases. They calculated the expansion would result in minimal increases in false-positive results (0.6%), over diagnosis (0.1%), and radiation-related lung cancer deaths (4%).
“Lung cancer rates are dropping, because smoking is decreasing, but that doesn’t mean that our current screening parameters are good enough,” Yang says. “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.”
She recommends additional research to confirm if similar trends are being seen in populations beyond Olmsted County Minnesota. If confirmed, she recommends that policymakers consider changing the lung cancer screening guidelines to include people who quit smoking more than 15 years ago. She also recommends that policymakers continue to re-examine lung cancer screening criteria to account for changes in groups that are most at risk.
Two-thirds of patients in the United States with newly diagnosed lung cancer would not meet the current U.S. Preventive Services Task Force (USPSTF) screening criteria, which suggests a need for amendment of the definition of high risk. To provide evidence of additional high-risk subpopulations and estimated gains and losses from using different criteria for screening eligibility, we conducted a two-step study using three cohorts.
The two prospective cohorts comprised 5988 patients in whom primary lung cancer was diagnosed between 1997 and 2011 (the hospital cohort) and 850 defined-community residents (the community cohort); the retrospective cohort consisted of the population of Olmsted County, Minnesota, which was observed for 28 years (1984–2011). Subgroups of patients with lung cancer who might have been identified using additional determinates were estimated and compared between the community and hospital cohorts. The findings were supported by indirect comparative projections of two ratios: benefit to harm and cost to effectiveness.
Former cigarette smokers who had a smoking history of 30 or more pack-years and 15 to 30 quit-years and were 55 to 80 years old formed the largest subgroup not meeting the current screening criteria; they constituted 12% of the hospital cohort and 17% of community cohort. Using the expanded criteria suggested by our study may add 19% more CT examinations for detecting 16% more cases when compared with the USPSTF criteria. Meanwhile, the increases in false-positive results, overdiagnosis, and radiation-related lung cancer deaths are 0.6%, 0.1%, and 4.0%, respectively.
Current USPSTF screening criteria exclude many patients who are at high risk for development of lung cancer. Including individuals who are younger than 81 years, have a smoking history of 30 or more pack-years, and have quit for 15 to 30 years may significantly increase the number of cases of non-overdiagnosed screen-detected lung cancer, does not significantly add to the number of false-positive cases, and saves more lives with an acceptable amount of elevated exposure to radiation and cost.