Ordinarily one would think that a decline in smoking rates would be beneficial from a public health perspective. But, according to a research letter published in the Feb. 24 issue of JAMA, such a decline could actually increase lung cancer mortality.

The problem, the researchers say, is that smokers who quit early and continue to abstain from smoking may not be eligible for low-dose lung cancer screening.

"As smokers quit earlier and stay off cigarettes longer, fewer are eligible for CT screening, which has been proven effective in saving lives," said co-author Ping Yang, MD., PhD., an epidemiologist at Mayo Clinic Cancer Center, in an announcement. "Patients who do eventually develop lung cancer are diagnosed at a later stage when treatment can no longer result in a cure."

In the study researchers retrospectively tracked residents of Olmstead County in Minnesota older than 20 between the years 1984 and 2011 and identified lung cancer cases using the Rochester Epidemiology Project database. They then determined the proportion of lung cancer patients who would have met the screening criteria established by the United States Preventive Services Task Force (USPSTF).

The USPSTF recommends screening for individuals aged 55 to 80 who smoked at least 30 pack-years and are still smoking, or have reduced consumption in the last 15 years.

According to the study, the proportion of lung cancer patients who would have been eligible for screening fell during the study period from 57% in the years 1984-1990 to 43% in 2006-2011, which means, Yang said, that many more patients are succeeding in quitting smoking, but also are missing out on the possibility of early detection of lung cancer.

Consequently, a change in screening criteria to include persons who smoked less than 30 pack-years and quit more than 15 years ago could be warranted, according to Yang.  "We don't want to penalize people who succeeded in smoking cessation," she said.