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Despite fewer smokers, poor screening criteria may raise lung cancer mortality
The decline in smoking rates will translate to fewer people qualifying for lung cancer screening with low-dose CT, thereby potentially leading to higher rates of lung cancer mortality, according to researchers at Mayo Clinic.
The U.S. Preventive Services Task Force issued a recommendation in December 2013 that annual lung cancer screening with low-dose CT be offered to adults aged 55 to 80 years who have a 30 pack-year smoking history and either still smoke or quit within the past 15 years. In February, CMS agreed to cover screening for Medicare beneficiaries aged 55 to 77 years who meet the same smoking criteria outlined in the USPSTF recommendation.
However, the percentage of American adults who smoke declined from 20.9% in 2005 to 17.8% in 2013, according to CDC.
“As smokers quit earlier and stay off cigarettes longer, fewer are eligible for CT screening, which has been proven effective in saving lives,” Ping Yang, MD, PhD, an epidemiologist at Mayo Clinic Cancer Center in Rochester, Minnesota, said in a press release. “Patients who do eventually develop lung cancer are diagnosed at a later stage when treatment can no longer result in a cure.”
In a retrospective study, Yang and colleagues evaluated data on about 140,000 people aged older than 20 years who lived in Olmstead County, Minnesota. They identified 1,351 individuals who developed incident primary lung cancer between 1984 and 2011.
Among that group, those who had a minimum 30 pack-year history of smoking declined during the study period, whereas the proportion of those diagnosed with lung cancer who had quit smoking more than 15 years prior increased during the study period.
This translated to a steady decline of patients with lung cancer who would have been eligible for lung cancer screening under current criteria.
From 1984 to 1990, 56.8% (95% CI, 50.8-62.9) of those in the study cohort diagnosed with lung cancer would have been eligible for low-dose CT scans. From 2005 to 2011, 43.3% (95% CI, 38.4-48.2) would have been eligible for screening.
The proportion of men who would have met smoking history criteria for screening declined from 60% to 50% during the study period, and the proportion of women who would have met smoking history criteria declined from 52.3% to 36.6%.
Policymakers and researchers must collaborate to change screening criteria to ensure a higher percentage of lung cancer cases are detected in early stages, Yang and colleagues concluded.
“The existing screening program will become less effective at reducing lung cancer mortality in the general population if they continue to use the same criteria,” Yang said. “We don’t want to penalize people who succeeded in smoking cessation.”
However, the researchers acknowledged there are potential dangers associated with relaxing lung cancer screening criteria too much. Those risks include higher costs, unnecessary radiation exposure and higher rates of false-positive results, which could lead to overtreatment.
“There are ways to screen at-risk patients while still avoiding false alarms,” Yang said in the release. “Researchers need to discover biological markers, such as genetic or physiological traits, to help them better identify high-risk patients.” – by Anthony SanFilippo
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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The majority of lung cancer deaths occur in people who do not meet the criteria for screening and, as we continue our efforts to decrease smoking rates, this proportion will inevitably increase. This is not, however, a reason to broaden the criteria so that more individuals are screened. To detect lung cancer in lower-risk individuals, we would have to screen increasing numbers, with higher and higher numbers needed to screen to detect one cancer.
The American Academy of Family Physicians has serious concerns about the potential harms of lung cancer screening using low-dose CT. These harms include effects of radiation from repeat CT scans, as well as false-positives, overdiagnosis and incidental findings, all of which lead to unnecessary evaluation, intervention and treatment.
The National Lung Screening Trial, upon which the screening recommendations are based, had a false-positive rate of approximately 30% with three annual CT tests, and an individual’s risk of eventually getting a false-positive increases with ongoing screening. If the criteria are broadened to include those at a lower risk for lung cancer, this false-positive rate will grow even larger and more patients will be put at risk. There also is a financial consideration. More lives would be saved by increasing efforts to help patients quit smoking, without the harms of false-positives and overdiagnosis.
Lung cancer is the leading cause of cancer death in both men and women, and catching it early can increase the likelihood of long-term survival. But there are tradeoffs. For example, research has revealed that past screening protocols for cervical, prostate and breast cancers contributed to unanticipated harms, thus leading us to less intensive screening protocols or stopping screening altogether. This history should inform our future decisions so that we don’t make the same mistakes.
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The study by Yang and colleagues points out that patients included in the National Lung Screening Trial — a randomized trial that evaluated annual low-dose spiral CT screening — excluded a number of patients who are at high risk for lung cancer. Among these might be patients who have had a lung cancer resected and are at risk for a second primary, and patients with a considerable smoking history who have chronic obstructive pulmonary disease (COPD), or patients who are more than 15 years since stopping smoking or who are outside the 55- to 75-year age group. Yang’s group showed that the number of patients who fit the NLST criteria may be decreasing, whereas the number of individuals at high risk who quit smoking more than 15 years prior to presentation may be increasing due to changes in smoking patterns in the United States.
Many studies have shown that patients with resected lung cancer have a higher-than-1% per year incidence of second primary lung cancer. In my opinion, these patients who were not included in NLST should receive annual low-dose CT. Yang’s letter indicates that heavy smokers who quit 15 years or more after smoking cessation are increasing in number and have a high rate of developing lung cancer. Because such individuals were not included in the NLST, we cannot be certain that low-dose CT would reduce lung cancer mortality in these patients. It is unlikely that a new randomized screening trial will be conducted. Thus, we will not be certain whether to offer low-dose CT screening to these patients. On the other hand, there are large efforts being undertaken to identify high-risk individuals, including blood, sputum or oral brushing analyses of protein signatures, gene signatures, miRNA signatures, or exhaled breath volatile organic compound signatures. Others are evaluating clinical risk features, including age at onset and cessation of tobacco smoking, presence of COPD or prior pneumonia, number of pack-years and other features. Until the results of such trials are completed, physicians must assess the risks and benefits of low-dose CT and have discussions with their patients in the decision process for who to screen.