Pamela A. Popper, Ph.D., N.D.
Wellness Forum Health
Accurate evaluation of a test, drug, or medical procedure depends on asking the right questions. Looking at the wrong issues can result in incorrect findings about the value of common medical practices. Take cancer screening for example. There is lots of debate about who should get screened, when screening should start, how often people should be screened. But much of this is a distraction from the real issue, which is whether or not cancer screenings actually reduce the risk of dying from cancer.
A research group at Oregon Health Sciences University in Portland reports that cancer screening has not had an effect on overall mortality, and that harms due to screening might actually contribute to increased rather than decreased mortality rates. The harms include false-positives which can result in unnecessary biopsies and treatment; and over-diagnosis which usually leads to treatment for a cancer that would be unlikely to become clinically significant or require treatment during a patient’s lifetime if left alone.
The researchers state that some studies show that cancer screening reduces cancer-specific mortality without reducing overall mortality, and that limitations in study design are the reason. For example, studies might not be designed to detect that reductions in disease-specific mortality are offset by deaths due to the effects of screening, which include over-diagnosis and over-treatment.
Cancer screening is promoted based on the assumption that early detection will lead to more opportunity for successful treatment. This then should result in lower cancer-specific death rates, which should then decrease overall mortality rates. But the Oregon State researchers say that the facts do not support this argument. They cite data from the National Lung Cancer Screening Trial as an example. Low-dose CT screening resulted in a small relative reduction in deaths from lung cancer when compared with chest X-ray, but only a tiny absolute reduction in overall mortality. Chest X-ray is now no longer the standard of care, and this change may actually have caused an increased risk of death from lung cancer. The researchers also point out that the estimated 12,000 fewer deaths from lung cancer resulting from CT scanning must be evaluated in consideration of the 27,034 major complications resulting from treatment, which include lung collapse, heart attack, stroke, and death.
The researchers encourage informed discussions between patients and doctors during which risks and benefits are evaluated, along with personal preferences. They wrote,
“Declining screening may be a reasonable and prudent choice for many people,” and added that “Doctors should be comfortable with whatever choice people make when they hear about all the potential benefits and the known harms.”
Much larger trials with millions of people would be required in order to determine if there is real value to screening tests. However, Gerd Gigerenzer, Ph.D., wrote in an accompanying article that instead of spending millions of dollars on huge trials looking for tiny reductions in mortality while inevitably harming more people, it would be better to just tell patients the truth about the limitations of screening and the existing studies. He suggests that for mammography, for example, information about screening should be presented in “fact boxes” that show the risks and benefits and state clearly how many women are affected. “It is time to change communication about cancer screening from dodgy persuasion into something straightforward,” he wrote.
Richard Schilsky, M.D., chief medical officer for the American Society of Clinical Oncology, says that the value of screening depends on three things. These are the degree of risk for the condition being screened, the sensitivity and specificity of the test, and the prognosis for the disease detected. He says there is little to be gained in screening for aggressive cancers for which there are no successful interventions because screening cannot change the outcome no matter how early the cancer is discovered. On the other end of the spectrum, there is no benefit to knowing about a cancer that is highly unlikely to become clinically significant. When all of these factors are considered, Schilsky says there is little benefit from cancer screening. He went on to say that most doctors do not understand these issues and the system does not allow them the time needed to engage in discussions about them.
This means that patients must take the initiative to find and evaluate this information in order to protect themselves against the excesses of medicine.
Prasad V, Lenzer J, Newman D. “Why cancer screening has never been shown to “save lives”—and what we can do about it.” BMJ 2016;352:h6080
Gigerenzer G. “Full disclosure about cancer screening.” BMJ 2016;352:h696
Neil Osterweil “Cancer Screening Has Not Been Shown to ‘Save Lives’”
Medscape January 07, 2016