Heavy smokers who kicked the butt as long as 15 years ago may continue to be at high risk of lung cancer, according to scientists who suggest that screening criteria for the disease should be adjusted to include such people.
Expanding lung cancer screening to include people who quit smoking more than 15 years ago could detect more cases and further reduce associated mortality, researchers said.
"A decline in smoking rates has been, and continues to be, a critical step to reduce lung cancer risk and deaths," said lead author Ping Yang, from the 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," Yang said.
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.
Previously, researchers had found that two-thirds of patients in the US 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, the 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 Minnesota in US.
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 did not qualify for screening.
The newly defined high-risk group constituted 12 per cent of the hospital cohort and 17 per cent of the community cohort.
"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," Yang said.
"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," Yang said.
"Lung cancer rates are dropping, because smoking is decreasing, but that doesn't mean that our current screening parameters are good enough," she said.
"We need to adjust screening criteria periodically, so we can catch more lung cancers in a timely fashion," she said.
The study was published in the Journal of Thoracic Oncology.
