Trends in Cancer Screening
Trends in Cancer Screening
Advocates of regular cancer screening say that early detection can save lives through diagnosis and treatment. Cancer screening research, however, paints a more complex picture that has raised questions about screening effectiveness, benefits versus risks, and implementation. The Innovations Exchange Team discussed these issues with Stephen Taplin, MD, MPH, an internationally recognized expert in the field of cancer screening for the National Cancer Institute, and Durado Brooks, MD, MPH, an expert in colorectal and prostate cancers with the American Cancer Society.
Innovations Exchange: Is cancer screening effective and how do you measure that?
Dr. Stephen Taplin: There is a consensus among cancer researchers that a decrease in cancer-specific mortality rates is the best indicator of screening's effectiveness. Analyses of randomized controlled trials comparing mortality rates of screened populations for breast, cervical, and colorectal cancers with nonscreened populations indicate that screening is effective. For example, women ages 50 to 70 in the United Kingdom offered regular breast cancer screening had an estimated 20-percent reduction in deaths from breast cancer compared with women not offered screening.
If cancer screening is effective at reducing mortality, what is the controversy about?
Taplin: After a few decades of cancer screening, researchers know more about its benefits, harms, and limitations. We know that screening doesn't prevent cancer or death from cancer in some people. We also know that screening poses risks for people who won't get cancer. Public health entities, including the United States Preventive Services Task Force (USPSTF), that make screening recommendations have evaluated the “net benefit” of screening the whole population by weighing the benefits of screening people who will get cancer against the risks of screening people who won't get cancer. As a result, the USPSTF revised some of its screening recommendations including recommending that women from age 40-49 not automatically be screened for breast cancer. The change was controversial and not adopted by the American Cancer Society.
What are potential risks of cancer screening that the USPSTF considers in developing its recommendations?
Taplin: The potential risks for people who won't get cancer include false positives (the diagnosis is inaccurate) and overdiagnosis (the cancer would not have affected the woman's life). Both false positives and overdiagnosis can cause anxiety and subject people unnecessarily to additional tests, procedures, and treatments that can be harmful. The potential risk of cancer screening for people who will get cancer is a false negative, in which the cancer is not detected.
What other factors influence the USPSTF's cancer screening recommendations?
Taplin: The speed of cancer development is a consideration in screening frequency. The task force recently lengthened the recommended screening interval from 1 to 2 years for breast cancer and from 1 to 3 years for cervical cancer. Both of these cancers are slow to develop.
The screening method also played a role in the USPSTF's colorectal screening recommendations. Colonoscopy, which uses a long flexible instrument attached to a video camera to examine the colon and rectum, can detect more polyps than can a fecal occult blood test (FOBT). As a result, the recommended colonoscopy screening interval is up to 10 years, compared with annual intervals for FOBT screening. With greater use of screening comes more recognition that we can be a little less aggressive and cause fewer side effects and harms by screening less often.
What is the status of prostate cancer screening recommendations?
Dr. Durado Brooks: The jury is still out as to whether the benefits outweigh the harms. The risks associated with prostate cancer screening are higher than those for breast, cervical, and colorectal cancers. Broad, unselective use of prostate-specific antigen (PSA) screening leads to overdiagnosis of individuals who otherwise would remain asymptomatic or would die from other causes. As a result, USPSTF recently issued a recommendation against the routine use of PSA screening, including in African-American men who have a high risk of developing and dying from prostate cancer.
Has screening research resulted in other revisions to USPSTF screening recommendations?
Taplin: The task force conducted a meta-analysis of the research on breast cancer screening before revising the age for starting routine breast cancer screening. The task force concluded that there was stronger evidence for women to start biennial screening at age 50 than at age 40. Although screening may reduce mortality in women age 40 to 49, the breast cancer rate is small in that population. The task force left the decision to screen at a younger age to women and their doctors, depending on their risk factors. The USPSTF recommended that the screening decision “should be an individual one and take patient context into account, including the patient's values regarding specific benefits and harms.”
Should physicians involve patients in making screening decisions?
Taplin: Physicians should discuss with patients what is known about cancer screening including the benefits, risks, and limitations. The discussion should also address the patient's values and priorities. This shared decisionmaking should be implemented for all cancers in all screening settings.
Brooks: The American Cancer Society, the USPSTF, and many other organizations recommend that clinicians engage in shared decisionmaking specifically about the PSA test, to ensure that men understand the benefits, harms, and limitations of screening before consenting to such testing.
About Stephen Taplin, MD, MPH: Taplin is the Branch Chief of the Process of Care Research Branch within the Division of Cancer Control and Population Sciences, Behavioral Research Program at the National Cancer Institute. He is an internationally recognized expert in the field of cancer screening and has been conducting research funded by the National Cancer Institute for most of his career. His work has included research on determinants of mammography use, factors affecting mammography interpretation, costs of cancer care, the evaluation of screening implementation, and multilevel interventions in cancer care delivery.
About Durado Brooks, MD, MPH: Brooks is the Director of Prostate and Colorectal Cancers for the American Cancer Society, is involved with creating and implementing strategies to improve the prevention and early detection of cancer, and works to assist those who are diagnosed with the disease. He is also actively engaged in American Cancer Society initiatives designed to eliminate disparities in cancer prevention, detection, and outcomes.
Disclosure Statement: Drs. Stephen Taplin and Durado Brooks reported having no financial interests or business/professional affiliations relevant to the work described in this article.