What is Screening?
Lung cancer is the leading cause of cancer deaths in the U.S. Why is the disease so fatal? One reason is that lung cancer does not often show symptoms until later stages when it has already spread and, therefore, has become difficult to cure. This makes early detection key and is why lung cancer screening so important. For those at risk, particularly for those who have smoked heavily and for a long time, screening could be a lifesaver.
It is important to first understand what cancer screening is about. Screening looks to identify cancer in its early stages before a person has symptoms. The hope is that, if a disease is found very early, then treatment may be curative. If a person has lung cancer symptoms, such as a cough that won't go away or coughing up blood, he or she may receive a CT scan. Receiving a CT scan once someone has symptoms is considered a diagnostic procedure instead of screening.
Lung cancer screening specifically targets high-risk individuals who don't have any symptoms of lung cancer. As of 2022, that group includes people between 50-80 years of age, who have a 20 or higher pack-per-year history of smoking and who currently smoke or have quit within the last 15 years. Early detection with low-dose CT screening can decrease lung cancer mortality by at least 20 percent among high-risk populations. So, if screening works with this high-risk group, why not screen everyone?
How Screening Tests are Developed
To address the above question, we need to think about the benefits and risks of screening and how they line up for different groups. Because there are risks to all screening tests and the procedures that may follow them in evaluating findings, physicians only recommend this test for populations most likely to benefit from it.
The process of recommending a screening test starts with large research studies, such as the National Lung Screening Trial (NLST). These studies compare what happens in a group randomly assigned to be screened in comparison to a group randomly assigned to the usual way of finding the disease. The NLST included more than 50,000 people who were at high risk for lung cancer. “The trial was designed to answer the question of whether an annual low-dose CT scan of the chest reduces death due to lung cancer,” says Andrea McKee, MD, a radiation oncologist and Lung Association volunteer medical spokesperson who specializes in the treatment and early detection of lung cancer. “A personal history of tobacco use and age are the two greatest risk factors for the development of lung cancer.”
The NLST found that the group who got low-dose CT had a 20 percent lower mortality rate from lung cancer than those who received chest x-rays. This is exciting news for people who meet the high-risk criteria. The results from the NSLT show that we have a way to detect lung cancer early in people who are at a high risk. Importantly, it shows that screening lowers the risk of death from lung cancer. “A screen detected stage IA lung cancer has a 90% chance of being successfully treated with surgery alone,” states Dr. McKee.
Focusing on the High-Risk Population
But what about other people who don't meet the criteria and are concerned about their risk because of exposure to radon at home or a family history of lung cancer? Currently the United States Preventive Services Task Force (USPSTF) defines the high-risk lung cancer population as individuals between the ages of 50 and 80 who have smoked at least 20 pack-years and currently smoke or have quit within the past 15 years. Dr. McKee notes “Screening this high-risk population in clinical practice has demonstrated a 2-3% risk of lung cancer detected in the baseline round of screening with a 1-2% chance of discovering new lung cancers in the later rounds of screening.”
Although people who don't meet the high-risk criteria can develop lung cancer, there is not enough evidence to know whether screening would be helpful or harmful for them. “The risk of finding lung cancer in those not at high-risk is considerably less than 1% and therefore the yield of cancer diagnosis resulting from the exam is quite small, offering minimal benefit. In this scenario, the risks from work-up, particularly bronchoscopy, needle aspiration, and surgery in those at low risk for the disease, outweigh the possible benefits of the exam."
One way to think about this is comparing lung cancer screening to screening for breast cancer in men. Men do get breast cancer, but they are at a much lower risk than women. If all men received mammograms, we would likely find many false positives or breast nodules that are harmless. Not only would this be a huge burden on the healthcare system, but this population would be exposed to radiation and potentially need invasive follow-up procedures, not to mention the emotional toll the process would take. When you weigh this against the chances that the test would correctly detect something that is cancer, it becomes clear the risks outweigh the potential benefits.
The Future of Lung Cancer Screening
As experts have more data, screening recommendations are often adjusted. This has happened in recent years with mammography and prostate and cervical cancer screening. In fact, additional research beyond the NLST has already contributed to our understanding of who is at high risk for lung cancer resulting in expansion of the USPSTF lung cancer screening guidelines to a broader population than what was studied in the NLST.
It is reasonable for people who have been touched by lung cancer in some way to be curious about their own risk, and many are because lung cancer is so common. However, it is also important to recognize that the lung cancer screening recommendations are in place to provide the largest health benefits to the greatest number of people possible. If you don't meet the high-risk criteria but are still concerned, it is best to talk to your doctor about ways you can reduce your risk. If for some reason other than smoking, you think that you are at high lung cancer risk, then ask your physician about whether you could benefit from screening. Your physician may need to consult an expert in this area. If you know people who are at a high risk, tell them about lung cancer screening and why it might be right for them. For more information, visit SavedByTheScan.org.
Thanks to Andrea McKee, M.D. for her expertise and guidance on this blog post.
Blog last updated: August 25, 2023