Early screening saves lives:
In conversation with Dr. Alain Tremblay medical lead, Alberta Early Screening for lung cancer Pilot project. University of Calgary
by Diane Colton, December 19, 2023
For many years now there have been screening protocols for breast, colon, and cervical cancers and it has made a big difference. For lung cancer where we know that early diagnosis will make as much of a difference as it has for the three above; it seems to be moving forward but always with barriers. Why is that? Why is the lung being looked at and treated so differently?
There are multiple reasons why lung cancer screening has taken so long to be implemented. From the scientific point of view, the main issue is that until 2011, we lacked evidence that low-dose cancer screening reduced mortality from this condition. Several large studies were done in the 1970s looking at chest X-rays and looking for abnormal cells in people's phlegm that did not demonstrate the effectiveness of these approaches. CT scans changed this; they can detect small lung cancers much earlier than a chest X-ray. In 2011 the National Lung Screening Trial in the United States demonstrated a 20% reduction in lung cancer mortality after screening for only 24 months. This was confirmed with the European NELSON trial published in 2019. These two trials changed the narrative on lung cancer screening and are why we're seeing all this progress today.
I know one of the areas of "concern" is the low-dose CT scan, but isn't the upside enough to offset the risk?
Many screening tests can have downsides. Some might relate to the test itself such as a radiation exposure associated with the CT scan in this case, or from downstream investigations resulting from false positive findings on the screen exams. For lung screening, this could involve additional scan appointments even biopsies or surgeries. Randomized trials show us that in high-risk individuals the upside of screening offsets the risk.
With the program in Alberta (and across the country) the qualifications seem to be limited in scope as to who can be screened. Why is that? It resolves around smokers/smoking, but the dynamics of lung cancer are changing, more people are being diagnosed who never smoked and at younger ages.
Lung cancer screening programs focus on high-risk individuals for a few reasons First lung malignancies remain overwhelmingly due to smoking cigarettes and tobacco. So, by screening high-risk individuals, we're much more likely to detect cancers and avoid the rare downsides of screening. This also makes programs much more cost-effective. Canadian programs are implementing sophisticated risk prediction models to enroll people in screening. This means that in addition to age and smoking history, other factors are also considered such as family history, race and ethnicity, and social demographic status to better define an individual's risk of lung cancer.
Unfortunately, these modern risk prediction models only capture approximately 60% of all lung cancers. However, we should remember that this is still a significant improvement compared to screening zero percent of the Canadian population as we had been doing previously.
We see lung cancers in younger patients, and in people that have minimally or never smoked cigarettes. Unfortunately, currently, we do not have an accurate way to identify these at-risk populations up front to offer screening. Screening 10,000 people or more to detect one lung cancer is not feasible in our system because it would be extremely expensive and potentially cause harm.
To deliver screening for a wider group of individuals a combination of two things would have to happen. First, our risk prediction model will have to improve and there is work ongoing to try to achieve this in Alberta and elsewhere. Second, screening intervention could also improve significantly to be more precise and eliminate the already minimal radiation exposure so that downsides become negligible and therefore the screening could be offered to a broader group of people with less concerns of harm.
Radon is also known to be a leading cause of lung cancer, yet it is not included in the criteria.
The main issue with radon is we don’t know how to quantify someone's exposure over long periods and incorporate that into risk modeling. You can test yourself but it is the last few decades of exposures that are important. Some online tools exist to try to quantify this which is a good start to figuring this out. Other researchers are looking at biomarkers that might allow us to estimate lifetime or long-term radon exposure. As these tools are validated, they could be incorporated into risk prediction models and lung cancer screening criteria. Ultimately, the solution to radon exposure is likely a building code and engineering one rather than a screening one.
Breast screening continues to evolve and the definition of who qualifies for screening is widening faster than for lung cancer. How does the stigma of lung cancer and smoking play a role in that?
The stigma around lung cancer and the marginalization of high-risk groups for this disease play a big factor in the slow pace of implementation of lung cancer screening. We've known for a long time that lung cancer research gets a tiny fraction of the dollars dedicated to other cancers such as breast and prostate. Even with clear evidence it is taking many years to convince funders (governments) to get behind this. One of the issues has been the lack of advocacy which also relates to the stigma associated with this disease. People with lung cancer, especially smokers, tend to blame themselves and do not speak out, or demand better care or research dollars. At the end of the day, governments respond to what the population demands of them. Researchers and clinicians can ask for funding all day long but until people ask their healthcare systems and governments to fund this, politicians and administrators can easily ignore the requests.
What should our screening programs look like and how can we get there?
The first and most urgent step is to start lung cancer screening on a wide scale across the country in an organized fashion. Once we're doing that, we need to continue improving the process and broadening the reach of screening. Of course, we can't forget about primary prevention – we should focus on the elimination of tobacco and other forms of smoking from our society and the mitigation of other risk factors such as radon exposure.
What will the impact of the radon clinical trial be on the screening landscape?
The radon work will allow us to better identify people at risk for lung cancer related to this exposure and perhaps allow us to screen such individuals. We do need to keep pressuring our governments to improve building codes in construction standards so that this becomes a nonissue in the first place.
The last word:
Lung cancer screening represents a breakthrough in our approach to lung cancer with a 20 to 25 percent reduction in mortality rates after a few years of screening which is likely to reach closer to a 75 percent reduction in mortality if people get screened over the entire age of their eligibility. It is not a perfect intervention and will not detect all lung cancers in our society, but we need to recall that currently almost no screening is going on and this disease remains the number one cause of cancer death in Canada. Even reaching 50% of individuals at risk would dramatically shift the landscape of this disease. The time to start broad-scale lung cancer screening in Canada is now.
ALCSI Podcast: Dr. Alain Tremblay
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