Each year, more people die of lung cancer than the other three cancers combined. Until recently, however, lung cancer screening efforts have not been effective.
Mammograms, colonoscopies, fecal occult blood testing and PSA testing are different approaches to achieve a common goal: detect and surgically remove a cancer before it spreads and takes a life. The benefits of screening have not been lost on lung specialists, but they have not had a reliable test.
Lung cancer also has few early symptoms. Only after the tumor is advanced do patients experience things like recurrent pneumonia, bloody sputum, shortness of breath or enlarged lymph nodes.
The early identification problem finally was tackled in the National Lung Screening Trial (NLST) by the National Cancer Institute. Researchers knew screening worked best in patients at high risk for developing lung cancer. They defined a set of characteristics common to lung cancer patients for selecting those included in the study.
The target population was identified as current or former smokers ages 55 to 75 who reported a 30-pack-year smoking history (30 pack years represents tobacco exposure of smoking a pack daily for 30 years, two packs per day for 15 years, etc.). Former smokers were included in the NLST study if they had quit in the past 15 years.
Low-dose CT imaging studies without contrast were used to limit known risks from radiation and contrast administration. (Contrast is a substance used to enhance the visibility of internal structures and occasionally can create problems.) Study participants received three low-dose CT scans or three chest X-rays annually to search for abnormal areas that could represent cancer.
Researchers pursued concerning abnormalities and identified many early-stage cancers. After years of screening, the group screened with low-dose CT imaging had a 20 percent lower chance of dying from lung cancer as compared to patients screened with a chest X-ray.
This trial was a screening breakthrough in a disease that had defied early detection.
While other cancer screening tests are recommended at certain ages, lung cancer screening is based on smoking history. That is why screening is not recommended for everyone.
Also, screening has distinct risks, including radiation exposure associated with CT imaging and risks with follow-up procedures. It will identify abnormalities that may not represent cancer. In fact, 1 in 4 of the imaging studies in the NLST trial exhibited such abnormalities. Pursuing abnormalities could lead to invasive procedures such as a bronchoscopy, CT-guided biopsy or even surgical procedures that may not have been needed.
Low-dose CT imaging and chest X-rays result in some radiation exposure. It is a small amount of radiation with each test, but a screening CT exposure is more than a chest X-ray and is about equal to the normal amount received from the sun in a year.
Considering the tens of thousands of people who fit screening criteria, a few will develop cancers associated with radiation from the imaging. These include breast, lung or thyroid cancers that develop many years later.
After considering these risks, it is clear that lung cancer screening is not meant for everyone. Those chosen need to receive the most benefit from the screening to justify the modest level of risk.
Does this mean that if you are not included in the groups above, you should not consider screening? The answer is a clear and resounding no. If you think you may be at high risk, raise those concerns with your doctor during your next visit.
The NSLT study was a breakthrough in screening, but is far from perfect. The study raises further concerns, such as how to screen patients at risk from second-hand smoke, environmental exposures, occupational exposures and those who may have smoked less than the 30-pack-year requirement.
As demonstrated with recent changes in prostate cancer screenings, screening recommendations remain fluid. The more we learn, the more we can refine our screening and the better we can serve our patients.
David W. Croy, MD, is department chair of Mercy Clinic Oncology and Hematology, 100 Mercy Way, Joplin. The clinic can be reached at 417.782.7722. Mercy Hospital Joplin is a Screening Center of Excellence by the national Lung Cancer Alliance for its ongoing commitment to responsible lung cancer screening.