In 2011, the New England Journal of Medicine published the primary results from the National Lung Screening Trial (NLST), which reported that patients who received low-dose helical computed tomography (CT) scans had a 20% lower risk of dying from lung cancer than participants who received standard chest x-rays.
Based on those results, the U.S. Preventive Services Task Force recommended annual low-dose CT screening for lung cancer in adults ages 55-80 who have a smoking history of at least 30 pack-years and who currently smoke or have quit within the past 15 years. And in 2015 the Centers for Medicare & Medicaid Services announced that Medicare would cover lung cancer screening with low-dose CT for eligible Medicare beneficiaries.
With the door open for both private and Medicare insurance coverage of lung cancer screening, it appeared that a mechanism was in place to reduce the high mortality associated with lung cancer.
But, according to a recent report from the American Lung Association (ALA), lung cancer screening rates among those who are at high risk for lung cancer remain low — 4.2% nationally, with rates that range from as high as 12.3% in Massachusetts to a low of 0.5% in Nevada.
The ALA report mirrors the findings of a recent study out of the University of Louisville, which showed an even slower uptake of lung cancer screening.
“We found out that the screening rate in the United States is extremely low,” study author Shruti Bhandari, MD, of the University of Louisville School of Medicine, told MedPage Today. Specifically, the team found that in 2016 just 2% of eligible smokers were screened, ranging from 1.1% in the West to 3.9% in the Northeast.
So, the obvious question is why, 8 years after the NLST reported its results, are lung cancer screening rates so low?
According to Andrea McKee, MD, a scientific advisor to the ALA and chair of radiation oncology at Lahey Hospital and Medical Center in Burlington, Massachusetts, there are several explanations, including the fact that lung cancer screening is still relatively new. “And it does take time for big changes in medical practice to make their way up through the ranks,” she said.
McKee told MedPage Today that she also believes that misconceptions about the potential harms of lung cancer screening are suppressing screening rates.
For example, “there is misinformation out there in the medical literature surrounding the false-positive rate of the exam,” she said. In particular, she noted that many articles have latched onto the figure of 96.4% as the exam’s false-positive rate.
This figure comes from the NLST, which reported that “across the three rounds, 96.4% of the positive results in the low-dose CT group and 94.5% of those in the radiography group were false positive results.”
The NLST also reported that of the total number of low-dose CT screening tests in the three rounds, “24.2% were classified as positive and 23.3% had false positive results.”
The 96.4% figure is actually the false discovery rate, said McKee, and along with false-positive rates are “both highly specific math equations and statistical definitions.”
“They are not open to interpretation,” she said. “It is a question of being very precise with language.”
As noted, the NLST’s false-positive rate was 23.3%, and when the Lung CT Screening Reporting and Data System (Lung-RADS) criteria were applied to the NLST’s results retrospectively, as it was in this study, the rate was reduced to 7.8%. A more recent study that applied Lung-RADS to an underserved urban lung cancer screening cohort reported a false-positive rate of 10.4%.
Accordingly, McKee said that when a physician is communicating with patients about false-positive rates, the conversation should go something like this: “For every 100 individuals undergoing CT lung screening, 90 will be negative, 10 are positive. Of the 10 that are positive, eight or nine turn out to be negative for cancer primarily with follow-up imaging alone.”
McKee said there have also been concerns about the issue of overdiagnosis. “But the rate is actually quite low for lung cancer, which makes sense since we know that lung cancer is quite deadly,” she said.
In fact, a recently published long-term follow-up of the NLST found that the overdiagnosis rate had decreased from 18% in the original analysis to just 3.1% with extended follow-up — “which is quite low,” McKee observed.
She also noted that there are “a lot of moving parts” when it comes to implementing lung cancer screening programs. These can include the need to train radiologists, educate partners such as primary care physicians and pulmonary and thoracic surgeons, set up smoking-cessation programs, and implement systems for tracking patients. “All of this takes time for centers to get straight, and we are in the process of seeing that right now,” she said.
According to Bhandari, there may be other reasons that the utilization rates of low-dose CT lung cancer screening are so low.
“Lung cancer screening can be complicated,” she said. “Many patients who are smokers and present in primary care offices have other issues that can be pressing, such as [chronic obstructive pulmonary disease] or diabetes, or hypertension. But for lung cancer screening specifically, primary care providers have to go into detail about eligibility criteria, and they have to do this shared decision-making that is required by Medicare and must be documented before they can be reimbursed.”
This is a process that has not been imposed for other forms of cancer screening, such as for mammography or colonoscopy, said Bhandari, and can be an additional barrier to increased screening.
In the meantime, other trials are showing an even greater mortality benefit from low-dose CT lung cancer screening than the NLST did.
For example, the Multicentric Italian Lung Detection (MILD) trial showed a 39% reduced risk of lung cancer mortality at 10 years with low-dose CT lung cancer screening, compared with the control arm, and a 20% reduction in overall mortality.
And the NELSON trial has reported that low-dose CT screening reduced the risk of death from lung cancer by 26% at 10 years, with an even higher reduction in women.
McKee serves as a scientific advisor to the American Lung Association.