A decline in smoking rates may mean that many people who could have benefited from early detection of lung cancer are dying because they don’t qualify for low-dose CT scans, according to a group of Mayo Clinic researchers. Their research appears in the Feb. 24 issue of JAMA, the journal of the American Medical Association.
“As smokers quit earlier and stay off cigarettes longer, fewer are eligible for CT screening, which has been proven effective in saving lives,” says Ping Yang, M.D., Ph.D., an epidemiologist at Mayo Clinic Cancer Center. “Patients who do eventually develop lung cancer are diagnosed at a later stage when treatment can no longer result in a cure.”
Dr. Yang says researchers and policymakers need to re-examine screening criteria to identify a greater proportion of patients who develop lung cancer.
“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,” Dr. Yang says.
The study retrospectively tracked residents of Olmsted County in Minnesota who were older than 20 years from 1984 through 2011 - about 140,000 people. Lung cancer cases were identified using the Rochester Epidemiology Project database and confirmed by pathology definition of the World Health Organization.
Researchers determined the proportion of lung cancer patients who would have met CT scan screening criteria set by the U.S. Preventive Services Task Force. Those criteria, used by doctors and insurance companies, recommend CT screening for asymptomatic adults age 55 to 80 who have smoked at least 30 pack-years (one pack a day for 30 years), and are still smoking or have reduced consumption in the last 15 years.
A total of 1,351 people in the study developed primary lung cancer between 1984 and 2011. Researchers found that the incidence of primary lung cancer fell overall during the study period - but only for men by about one-third. Among women, the incidence of lung cancer rose 8 percent.
The cigarette smoking rate among adults in the U.S. dropped from 20.9 percent in 2005 to 17.8 percent in 2013, according to new data published by the Centers for Disease Control and Prevention in today’s Morbidity and Mortality Weekly Report (MMWR).
That is the lowest prevalence of adult smoking since the CDC’s National Health Interview Survey (NHIS) began keeping such records in 1965. The report also shows the number of cigarette smokers dropped from 45.1 million in 2005 to 42.1 million in 2013, despite the increasing population in the U.S.
“There is encouraging news in this study, but we still have much more work to do to help people quit,” said Tim McAfee, M.D., M.P.H., director of the CDC’s Office on Smoking and Health. “We can bring down cigarette smoking rates much further, much faster, if strategies proven to work are put in place like funding tobacco control programs at the CDC-recommended levels, increasing prices of tobacco products, implementing and enforcing comprehensive smoke-free laws, and sustaining hard-hitting media campaigns.”
While smoking rates have dropped, there is a significant need to help those who continue to smoke. Cigarette smoking remains especially high among certain groups, most notably those below the poverty level, those who have less education, Americans of multiple race, American Indians/Alaska Natives, males, those who live in the South or Midwest, those who have a disability or limitation, and those who are lesbian/gay/bisexual. Data specific to sexual orientation were collected for the first time by the NHIS in 2013.
Among current cigarette smokers, the proportion of those who smoke every day decreased from 80.8 percent in 2005 to 76.9 percent in 2013. The proportion of cigarette smokers who smoke only on some days increased from 19.2 percent in 2005 to 23.1 percent in 2013. Among daily smokers, the average number of cigarettes smoked per day declined from 16.7 in 2005 to 14.2 in 2013. The proportion of daily smokers who smoked 20 to 29 cigarettes per day dropped from 34.9 percent in 2005 to 29.3 percent in 2013, while the proportion who smoked fewer than 10 cigarettes per day rose from 16.4 percent in 2005 to 23.3 percent in 2013.
According to Dr. Yang, the data with greatest relevance to CT screening is the proportion of lung cancer patients who smoked at least 30 pack-years which declined over the study period. And the proportion of cancer patients who had quit for more than 15 years increased. “While more people have quit for a longer period of time, they are still getting lung cancer,” Dr. Yang says, “and they make up a larger proportion of newly diagnosed lung cancer patients.”
As a result, the proportion of lung cancer patients who would have been eligible for screening fell steadily during the study period - from 57 percent in 1984-1990 to 43 percent in 2005-2011. The proportion of women who would have been eligible under the criteria decreased from 52 percent to 37 percent, and among men from 60 percent to 50 percent.
That trend has important consequences, says Dr. Yang.
Why Smoking Rates Are at New Lows
The smoking rate among adults in the United States has dropped again, an encouraging trend that experts on smoking cessation attribute to public policies like smoke-free air laws and cigarette taxes, as well as media campaigns and less exposure to smoking in movies.
Eighteen percent of American adults were cigarette smokers in 2012, according to a report released last week by the National Center for Health Statistics, down from 18.9 percent the previous year. From 2009 to 2012, the rate dropped to 18 percent from 20.6 percent, the first statistically significant change over multiple years since the period spanning 1997 to 2005, when the rate fell to 20.9 percent from 24.7 percent.
“The fact that we’re below this theoretical sound barrier of 20 percent is important,” says Stanton A. Glantz, a professor of medicine at the University of California, San Francisco, and director of the university’s Center for Tobacco Control Research and Education. “This data shows that the whole premise that there is this hard-core group, where no matter what you do you can’t get them to quit, is just not true.”
First, many more patients will miss out on early detection, when treatment of lung cancer is most successful. “That means more patients are going to be diagnosed at a later stage, because they could not take advantage of early detection,” she says. As a result, more patients will die.
Second, Dr. Yang hopes to see screening criteria adjusted to include smokers who have smoked less than 30 pack-years and those who quit more than 15 years ago. “We don’t want to penalize people who succeeded in smoking cessation,” she says.
Dr. Yang says she is aware of many smokers who are cancer-free but continue to smoke in order to be eligible for CT screening.
Third, CT screening - the only screening technology proven to save lives among patients with lung cancer - will become less and less effective unless screening criteria are revised to include more patients who are likely to develop cancer.
Dr. Yang acknowledges there is a danger in relaxing CT-screening criteria too much, citing concerns about cost, radiation exposure and overtreatment due to false positives that increase patient pressure on physicians to remove tumors even if they do not appear dangerous.
“There are ways to screen at-risk patients while still avoiding false alarms and overtreatment,” says Dr. Yang. “Researchers need to discover biological markers, such as genetic or physiological traits, to help them better identify high-risk patients.” She says screening criteria might also be adjusted to include some smokers who have smoked less than 30 pack-years or quit more than 15 years ago. Dr. Yang says she and her colleagues are preparing papers on these issues to develop proposals for more effective CT screening that will save more lives from lung cancer.
The study was supported by grants from the National Institutes of Health, a grant from the National Institute on Aging, and funding from the Mayo Clinic Foundation.
Co-authors include David Midthun, M.D., Jason Wampfler, B.S., of Mayo Clinic; and Yi Wang, M.D., of Medical University, Whenzhou, China.
About Mayo Clinic Cancer Center
As a leading institution funded by the National Cancer Institute, Mayo Clinic Cancer Center conducts basic, clinical and population science research, translating discoveries into improved methods for prevention, diagnosis, prognosis and therapy. For information on cancer clinical trials, call 1-855-776-0015 (toll-free).