More than 220,000 men and women in the United States will be diagnosed with lung cancer this year. More than 160,000 will die of the disease, making it by far the number one cancer killer. Three times more men die of lung cancer than prostate cancer. More women will die of lung cancer than of breast, uterine, and ovarian cancer combined.
Despite the fact that there has been progress in the treatment of lung cancer, there has never been a proven screening test for it. Prior efforts at screening for lung cancer using chest x-ray and tests of sputum (phlegm) did not work well enough to save lives. Chest CT (computed tomography) screening for lung cancer has always held promise, but concerns regarding the potential for abnormal test results not due to cancer (false positives), as well as no evidence that CT screening prevented death from lung cancer, have delayed its use as a screening tool.
Lung Cancer Risk
Although people who have never smoked cigarettes can get lung cancer, smoking remains the strongest and most important preventable cause of this disease. Individuals who have never smoked are at relatively low risk for lung cancer, while people who have smoked but recently quit and those who continue to smoke are at ten to 20 times the risk of people who have never smoked.
Other risk factors, such as occupational asbestos and environmental radon, remain important in lung cancer causation, but their effects are small relative to the impact of smoking on lung cancer. Memorial Sloan Kettering has an online tool that people can use to determine their risk of lung cancer, but it only works for people with a substantial level of risk such as those for whom CT screening is effective.
Our Guidelines for CT Screening for Lung Cancer
Prior to the release of the National Lung Screening Trial (NLST) results in November 2010, which showed that CT screening of high-risk individuals reduced their risk of lung cancer death, no organization recommended routine screening for lung cancer.
The National Cancer Institute trial results will change many organizations' recommendations. Memorial Sloan Kettering now recommends the following:
- Persons aged 55 to 74 with no history of cancer, or who have been cancer-free for five years,* and who have smoked at least one pack of cigarettes per day for 30 years (30 pack years) should be screened with low-dose helical CT of the chest. (A “pack year” is a term used to describe the number of cigarettes a person has smoked over his or her lifetime. One pack year is defined as 20 cigarettes – one pack – smoked per day for one year.)
- Such individuals should have low-dose CT of the chest once a year for a total of three times.
* The requirement of having no cancer history or being cancer-free for five years does not apply to individuals with non-melanoma skin cancer.
Additional interventions should include smoking cessation counseling or referral for all current smokers
Special Considerations for Screening of Survivors of Cancer
There is very little data on the benefit of screening patients with cancer for other malignancies. With the steady increase in survival among people with cancer, the risks of developing another cancer and dying from it are also increasing. Patients with cancer are at high risk for developing additional cancers for a variety of reasons: exposure to environmental factors (such as cigarette smoke) predisposing them to numerous cancers; effects of cancer therapy; and, possibly, shared predisposing genetic factors among different cancers.
Therefore, patients whose cancer has been cured or brought under control and have a reasonable life expectancy should undergo screening proven to be beneficial in the general population. Modifications to the screening program (start at an earlier age, more frequent screening) may need to be made and screening modalities not necessarily recommended for the general population may be used. Such decisions must be tailored to the tumor and the patient.
Additional Information about CT Screening for Lung Cancer
CT screening for lung cancer has only been studied in people at high risk of lung cancer — those with a long smoking history and who are 55 and older. For these individuals, the ten-year risk of developing lung cancer is greater than one in 100. For younger people and those with less smoking exposure, the risks are lower.
In the National Lung Screening Trial (NLST), lung cancer mortality was decreased by 20 percent in a high-risk population of heavy smokers who underwent three scans at one-year intervals. These were low-dose helical (also known as spiral) CT scans of the chest. Trial patients had no history of cancer in the preceding five years. The CT uses x-rays to obtain a multiple-image scan of the entire chest during a single breath hold.
Individuals who are considering being screened for lung cancer with CT should know that the risks of the procedure have not been fully defined and that the benefit is relatively small.
In the study, for every 300 people who were screened, one death from lung cancer was averted. The risk that people who are screened with CT develop other cancers from the radiation was not quantified, but is likely to be far outweighed by the benefits of detecting lung cancer at an earlier, more treatable stage. Numerous studies do warn of other harms from CT screening, as CT is a highly sensitive test that identifies numerous abnormalities that are not cancer. Finding these abnormalities can cause anxiety and lead to further evaluation. In the first CT scan in the NLST study, such abnormalities were seen in one-quarter of patients. I n other studies, the frequency has been as high as 40 to 50 percent of patients. Evaluation of these abnormalities can cause complications and can sometimes lead to unneeded operations during which a portion of the lung is removed.
The low-dose chest CT used for screening delivers a much lower amount of radiation than a conventional CT. The radiation dose of a low-dose CT scan is equivalent to about 15 chest x-rays and is five times lower than the dose from a conventional CT scan. The radiation dose of a low-dose CT can also be compared to about 50 cross-country flights or six months of natural background radiation. Typically, a low-dose CT will deliver an effective dose of between 1 and 4 millisievert, whereas a conventional chest CT delivers an effective dose of about 5 to 20 millisievert, depending on the size of the patient. Studies are in progress to assess the lifetime risk of low-dose screening CT scans. In the NLST study that began in 2002, the overall death rate from all causes was lower among the patients who underwent the three low-dose helical chest CT scans than in patients who had three chest x-rays instead.
Patients with cured or active cancer undergoing standard yearly surveillance chest CTs as part of their cancer care will not need an additional low-dose helical CT of the chest. For patients with active or cured cancer requiring chest CT surveillance, a low-dose helical CT of the chest is not a substitute. Nor is PET scan a substitute for a low-dose helical CT of the chest in patients appropriate for screening.
Lung cancer screening is not a substitute for smoking cessation. Anyone considering screening who is still smoking should receive smoking cessation counseling. Current Memorial Sloan Kettering patients can ask their physicians for a referral to our Smoking Cessation Program.