Usually symptoms of lung cancer don’t appear until the disease is already at an advanced, non-curable stage. Even if lung cancer does cause symptoms, many people may mistake them for other problems, such as an infection or long-term effects from smoking. This may delay the diagnosis.
Some lung cancers are found early by accident as a result of tests for other medical conditions. For example, lung cancer may be found by tests done for other reasons in people with heart disease, pneumonia, or other lung conditions. A small portion of these people do very well and may be cured of lung cancer.
Screening is the use of tests or exams to find a disease in people who don’t have symptoms. Doctors have looked for many years for a good screening test for lung cancer, but only in recent years has a study shown that a test known as a low-dose CT (LDCT) scan can help lower the risk of dying from this disease.
The National Lung Screening Trial
The National Lung Screening Trial (NLST) was a large clinical trial that looked at using LD CT scan of the chest to screen for lung cancer. CT scans of the chest provide more detailed pictures than chest x-rays and are better at finding small abnormal areas in the lungs. (Both of these tests are discussed in more detail in Exams and tests to look for lung cancer.) Low-dose CT of the chest uses lower amounts of radiation than a standard chest CT and does not require the use of intravenous (IV) contrast dye.
The NLST compared LDCT of the chest to chest x-rays in people at high risk of lung cancer to see if these scans could help lower the risk of dying from lung cancer. The study included more than 50,000 people aged 55 to 74 who were current or former smokers and were in fairly good health. To be in the study, they had to have at least a 30 pack-year history of smoking. A pack-year is the number of cigarette packs smoked each day multiplied by the number of years a person has smoked. Someone who smoked a pack of cigarettes per day for 30 years has a 30 pack-year smoking history, as does someone who smoked 2 packs a day for 15 years. Former smokers could enter the study if they had quit within the past 15 years. The study did not include people if they had a prior history of lung cancer or lung cancer symptoms, if they had part of a lung removed, if they needed to be on oxygen at home to help them breathe, or if they had other serious medical problems.
People in the study got either 3 LDCT scans or 3 chest x-rays, each a year apart, to look for abnormal areas in the lungs that might be cancer. After several years, the study found that people who got LDCT had a 20% lower chance of dying from lung cancer than those who got chest x-rays. They were also 7% less likely to die overall (from any cause) than those who got chest x-rays.
Screening with LDCT was also shown to have some downsides that need to be considered. One drawback of this test is that it also finds a lot of abnormalities that have to be checked out with more tests, but that turn out not to be cancer. (About 1 out of 4 CT scans in the NLST showed such a finding.) This may lead to additional tests such as other CT scans or more invasive tests such as needle biopsies or even surgery to remove a portion of lung in some people. These tests can sometimes lead to complications (like a collapsed lung) or rarely, death, even in people who do not have cancer (or who have very early stage cancer)
LDCTs also expose people to a small amount of radiation with each test. It is less than the dose from a standard CT, but it is more than the dose from a chest x-ray. Some people who are screened may end up needing more CT scans, which means more radiation exposure. When done in tens of thousands of people, this radiation may cause a few people to develop breast, lung, or thyroid cancers later on.
Can Non-Small Cell Lung Cancer Be Found Early?
Last Medical Review: February 18, 2016 Last Revised: February 22, 2016
https://www.cancer.org/cancer/lung-cancer/prevention-and-early-detection/early-detection.html
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