Lung cancer is the number one cancer killer of both men and women. 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. This makes early detection key and lung cancer screening so important for those at risk, particularly for those who have smoked heavily and for a long time.
It is important to first understand what cancer screening is about. Screening is looking for cancer in its early stages before a person has symptoms. The idea is that if a disease is found very early then a treatment can prevent the disease from developing. If a person has symptoms of lung cancer, 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 looks for lung cancer in high-risk individuals who don't have any symptoms of lung cancer. The group targeted for screening in the U.S. is people between the ages of 55-80 years of age, who have a 30-pack-per-year history of smoking and are current smokers or have quit within the last 15 years. Early detection with low-dose CT screening can decrease lung cancer mortality by up to 20 percent among high-risk populations. So, if screening works with this high-risk group, why not screen everyone?
How Screening Tests are Developed
In order 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 to find the disease. The NLST included more than 50,000 people who met the age and smoking status criteria listed above. "The criteria were intended to assure that the trial would have a high-risk study group so that it could meet the overall scientific goal of testing whether low-dose CT screening reduces mortality," said Jonathan M. Samet, M.D., M.S., a pulmonary physician and epidemiologist and professor and chairman at the University of Southern California Keck School of Medicine. "Never smokers were not included because of their comparatively low risk for lung cancer, about 20 times less."
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 of the NLST. The results from the NSLT show that we finally 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.
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? 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. Dr. Samet notes that in this low-risk population, "There is far more likelihood of turning up something that may look like lung cancer and require a potentially invasive and expensive work-up, and there are risks from work-up, particularly bronchoscopy, needle aspiration, and surgery." Dr. Samet goes on to say the main reason not to screen for groups outside the recommended high-risk population is the "low predictive value" of the test. "The test is not likely to capture ‘real' disease but yield false positives." Dr. Samet also said that "costs, not only economic, but the risks of work-up and the stress from needlessly being told that there may be a cancer" are reasons not to screen people that are not at a high risk. The predictive value of a test declines as the disease it looks for becomes less common. If we screen large groups of people who do not meet the high-risk criteria, we will get too many false positives and could divert much needed resources from the population that could benefit from the screen.
Public Health vs. Individual Health
One key word that often appears in discussions of screening is "population." The development and implementation of screening guidelines falls into the field of public health. This can be a difficult concept to understand because cancer feels so personal. It can be challenging to think about how screening can affect the health of the larger public.
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, 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 actually 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, there are additional research studies going on to examine if those with a lower risk of lung cancer would benefit from screening. But Dr. Samet doesn't predict any immediate expansion of the guidelines. "Perhaps, if we ever have a much deeper understanding of the genetics of lung cancer, there may be some genetically at-risk groups for whom risk is high enough to warrant screening," he said. He goes on to say that the same rational might be able to be used for other risk factors like high radon exposure.
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 Lung.org/lcscreening.
Thanks to Jonathan M. Samet, M.D., M.S., for his expertise and guidance on this blog post.