The Benefits and Harms of Cancer Screening
Dr. Otis Brawley
Screening is looking for cancer in an asymptomatic individual only because he or she is the age or gender of people at risk for the disease.
While the wise use of screening tests can save lives, and screening is one important element in the 20 percent decline in the cancer death rate over the last 20 years, screening is complicated.
As a screening expert, I worry that many people view these issues too simplistically. Cancer screening should be practiced with some caution. In assessing the science behind common screening tests, most expert panels have advised that the patient be told about the potential risks and benefits associated with a screening test, as well as the diagnostic tests and treatments associated with a positive result.
Patients should understand that no screening test is 100 percent accurate. Any test will miss some cancers. For example, high-quality mammography misses at least 20 percent of tumors, and prostate cancer screening misses at least half of all prostate cancers. Screening can also cause anxiety. And, in rare cases, screening can lead to treatment and diagnostic interventions that can even cause an early death.
In some cases, screening can find an early cancer, yet still lead to unnecessary treatment and all of the side effects associated with the treatment. These cancers are overdiagnosed. They fulfill all the criteria for cancer and look like cancer under a microscope, but if left alone they will not progress and kill. Some studies suggest that about one-third of screen-detected localized breast cancers and up to 70 percent of localized prostate cancers are overdiagnosed. A number of other cancers, especially cancers of the thyroid and lung, are also overdiagnosed.
Because of overdiagnosis, greater survival time after diagnosis or larger proportions of patients alive 5 years after diagnosis are not necessarily evidence of benefit from screening. This is because some patients might have been overdiagnosed, and some patients may have been diagnosed earlier but not lived longer. (See “Crunching the Numbers:What Cancer Screening Statistics Really Tell Us.”)
Nevertheless, screening is an important part of the effort to reduce the number of lives lost to cancer. And, as this special issue of the NCI Cancer Bulletin highlights, a tremendous amount of research focused on improving the effectiveness and efficiency of cancer screening is under way.
Many investigators, for example, are developing the next generation of screening tests for a host of cancers. This is painstaking research that requires patience and perseverance, but the progress to date is encouraging.
Other researchers are trying to solve one of the most persistent and pernicious problems in cancer care—and our health care system as a whole: disparities. Any gynecologic oncologist will tell you that Pap and HPV testing can prevent cervical cancer. But they will also tell you that they are treating too many women—in many cases, African American women or those without health insurance—with late-stage cervical cancer who were inadequately screened or never screened at all. An innovative program, called PROSPR, is aimed at reversing that trend by improving the entire cancer screening process, with a particular focus on underserved populations.
Another effort, called CISNET, is using sophisticated computer modeling to find how best to extrapolate the results of cancer screening studies, including large randomized trials, to the general population. This work includes a deeper analysis of the results of the National Lung Screening Trial, a study that focused on people at high risk for lung cancer based on their smoking history.
This special issue of the NCI Cancer Bulletin also includes several discussions with noted screening experts about interpreting cancer screening statistics and how we think and talk about screening, especially during conversations between patients and physicians.
The breadth of the research being done to improve how we screen for cancer is extremely encouraging. Although progress may not always come as quickly as we might like, given the expertise and dedication of investigators working in this area, the future holds great promise.
Dr. Otis W. Brawley
Chief Medical and Scientific Officer, American Cancer Society
Professor of Hematology, Medical Oncology, Medicine, and Epidemiology, Emory University
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