Several types of cancers have effective screening approaches that are used to regularly check people who are at high risk for developing those cancers, including mammograms for breast cancer and colonoscopies for colon cancer. A low-dose computed tomography (CT) scan is a screening that can be done for people who are at an increased risk of developing lung cancer.
Lung cancer is the second most common type of cancer in the United States for both men and women, and it is the leading cause of cancer deaths. Lung cancer is best treated when it is found at an early stage, when the cancer is still localized (stage 1 lung cancer in non-small cell lung cancer or limited-stage cancer in small cell lung cancer).
Unfortunately, less than 20 percent of lung cancers are diagnosed before the tumor has spread. At an early stage, many people do not experience any symptoms of lung cancer, making detection even more difficult. Early lung cancer screenings that can help catch cancer before symptoms develop offer the best chance of diagnosing and treating cancer early.
Not everyone will benefit from screening — for example, screening won’t identify all types of cancer in their early stages. Guidelines also advise what ages and what kind of smoking exposure qualify people for lung cancer screening. If you are at an increased risk for lung cancer, talk to your doctor about early screening and if you qualify.
Early screening for lung cancer is done using a low-dose CT scan (LDCT), also known as a helical CT scan or a low-dose spiral CT scan. The LDCT scan exposes you to less radiation than a traditional CT scan and does not require contrast dye. The LDCT is highly sensitive and can create detailed images of the lungs to look for abnormalities.
The National Lung Screening Trial (NLST) was a large, randomized clinical trial that studied the difference between low-dose CT and X-ray as screening methods for lung cancer.
The NLST included more than 50,000 people between the ages of 55 and 74 who had currently or previously smoked and were generally in good health, without symptoms of lung cancer. In order to be eligible for the study, the participants had to have at least a 30 pack-year smoking history.
Overall, the study found that people who were screened using LDCT were 20 percent less likely to die from lung cancer than those who had chest X-rays.
CT scans can be used to take detailed images of the chest and are better for finding small, abnormal spots in the lungs compared to chest X-rays. The study also found that specific subtypes of non-small cell lung cancer, such as squamous cell carcinomas and adenocarcinomas, were more likely to be detected early using LDCT compared to chest X-rays. On the other hand, small cell lung cancers are much more aggressive and less likely to be detected early by either LDCT or chest X-rays.
Screening is typically recommended only for people who are at a high risk of developing lung cancer. The people who are at the highest risk are current smokers and former smokers who have smoked a certain number of cigarettes per year. Smoking history is quantified using pack-years. One pack-year is equivalent to smoking one pack (20 cigarettes) per day for one year. For example, a 30 pack-year smoking history can mean a person smoked one pack a day for 30 years, or two packs a day for 15 years.
Several organizations have developed guidelines indicating who should be screened. These guidelines rely mainly on the results from the National Lung Screening Trial.
The U.S. Preventive Services Task Force (USPSTF) recommends annual screenings using LDCT for adults who meet all of these criteria:
The USPSTF recommends stopping lung cancer screening once a person meets any one of these criteria:
The American College of Chest Physicians recommends annual screening with LDCT for adults who meet all of these criteria:
The National Comprehensive Cancer Network divides its recommendations for annual lung cancer screening with LDCT into two groups for adults who are either:
Other risk factors that increase your risk of developing lung cancer include exposure to asbestos, having a family history of lung cancer, and having chronic obstructive pulmonary disease.
Your LDCT scan will be performed and then analyzed by a radiologist, a doctor who specializes in reading imaging tests. If they do not find any abnormalities, your doctor will likely recommend you continue annual screening tests to monitor your lungs.
The radiologist may also find lung nodules, which look like small spots in the lungs. These nodules are not always cancer and could be from other conditions, such as benign (noncancerous) growths or scarring from past infections.
Fortunately, only around 4 percent of lung nodules found in screenings are cancerous. Many small nodules can be monitored with annual screening. In some cases, your doctor may ask you to return for a scan in a few months to check if the nodule has grown, which may be a sign of cancer. Then, it would be biopsied to find the definitive answer.
If your scan shows larger nodules, you may be referred to a pulmonologist — a doctor who specializes in the heart and lungs. This doctor can perform additional tests on the nodule, such as a biopsy, to see if it is cancerous. A biopsy involves removing a piece of the nodule and looking at it under a microscope for cancer cells.
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