Former and ‘light’ smokers who fall outside lung cancer screening guidelines are still at risk compared to never-smokers.
Older smokers who fall outside lung cancer screening recommendations in the US have a 10-fold higher risk of lung cancer compared with never smokers, research has found.
The study in JAMA Oncology calculated the risk of lung cancer in former smokers and “light” smokers, who are not normally eligible for annual low-dose computed tomography (LDCT) lung screening in the US.
The cohort study included more than 4000 people aged 65 or older with a history of smoking who were followed up for 13 years.
During the study period, lung cancer occurred in 10 of 1973 never smokers (0.5%), 5 of 100 current nonheavy smokers (5%), and 26 of 516 former heavy smokers with 15 or more years of smoking cessation (5%).
The researchers said their findings suggest that prediction models were needed to identify high-risk subsets of smokers for screening.
“Former smokers with a 20 pack-year or greater smoking history who quit 15 or more years before baseline and current smokers with less than 20 pack-years of smoking (2 groups not recommended for lung cancer screening) had a 10-fold greater risk of lung cancer than never smokers,” the researchers wrote.
“Although this risk was lower than that of smokers for whom annual LDCT screening is recommended, a 10-fold higher risk suggests that future studies should assess whether LDCT screening may reduce lung cancer mortality in this population.”
Under the US Preventive Services Task Force’s guidelines, annual LDCT lung cancer screening is not recommended for current smokers with less than 20 pack-years of smoking, or for adults aged 50 to 80 who are former smokers with 20 or more pack-years of smoking who quit 15 or more years ago.
Cancer epidemiologist Associate Professor Marianne Weber, who leads the lung cancer policy and evaluation stream at The Daffodil Centre, said the paper highlighted that smoking at any intensity for any length of time significantly increased the risk of lung cancer.
“However, the study doesn’t directly assess how these smoking-related lung cancer risks play out in an actual screening program or screening study,” Professor Weber told Oncology Republic.
The benefits of a screening program need to be weighed against the risks and potential distress of false positives and incidental findings, she said.
“We would want to know at what point do the benefits of screening outweigh the harms for these individuals.
“It’s important to target the appropriate population for a lung screening program. It’s important for maximising the potential benefits of screening and minimising the unwanted harms, added costs of false positive findings over treatment of indolent lesions, unnecessary radiation exposure and increased use of primary and secondary care resources.”
Professor Weber said randomised controlled trials of lung cancer screening had found that 22-50% of participants had lung nodules, but only 1-3% developed lung cancer.
“It makes sense to screen everybody who’s ever smoked a cigarette, but there has to be a cut point somewhere. It’s a matter of determining your definition of high risk.”
Professor Weber said that even with risk tools, there would still be people diagnosed with lung cancer who were not eligible for screening.
“At the moment, based on current evidence, lung cancer screening is not recommended for people that have never smoked, and about a third of lung cancers occur among women who have never smoked,” she said.
“A lung cancer screening program using a low-dose CT scan isn’t for everybody, but it will do a lot of good for those who are at high risk or who are eligible.”
Professor Weber said the evidence for a lung cancer screening program was slowly accumulating.
“Hopefully Australia will be in a good position to roll out something that’s effective and acceptable.”
What about the risks of ‘so-called light smoking’?
“Pack-years is not a great way to gauge risk from smoking – exposure in terms of cigarettes per day and risk are by no means linearly related,” said Professor Matthew Peters, Head of Respiratory Medicine at Concord Hospital.
The Sydney-based respiratory physician said the paper highlighted the importance of early smoking cessation and of not dismissing the harms of “so-called light smoking”.
Professor Peters told Oncology Republic that lung cancer screening, or “case detection”, was justified in patients with an absolute risk of lung cancer of 1.5% or more in a projected six-year period.
“This threshold is based on proven benefits and proven or reasonably estimated harms. Composite risk prediction models incorporate some factors other than smoking.
“There are certainly ‘lighter’ smokers and ex-smokers who have higher risk than never smokers but are below the absolute risk threshold,” Professor Peters said.
Under the Medical Services Advisory Committee’s recommendation of a national lung cancer screening program, Australians aged between 50 and 70 with a significant history of smoking and who were continuing smokers or had quit within 10 years would be eligible for LDCT screening every two years.
“These parameters are not ideal and I strongly favour using composite risk prediction,” Professor Peters said.
“That said, now may not be the time to be fiddling with thresholds because it feeds into the ‘thin edge of the wedge’ concerns. Implementation could be further delayed and the opportunity to save lives missed.”
Professor Weber also noted the challenge of attracting people to screening programs, especially priority populations who experienced barriers to health services.
“Participation rates in other screening programs aren’t optimal, that’s for sure. And if people suffer stigma from smoking, they are probably less likely to go and see a doctor,” she pointed out.
“Bowel cancer screening has not been shown to reduce overall mortality and there is another paper just out in NEJM that shows exactly that for colonoscopy-based bowel cancer screening. Don’t start me on prostate cancer ‘screening’ using PSA,” said Professor Peters.
“Lung cancer screening in high-risk persons reduces lung cancer specific mortality and overall mortality. But lung cancer is not sexy and it has been a huge battle to get even this far.”