-Loralie Ma, M.D.
Screening Tests, Epidemiology and the Individual
Screening tests are ever increasing, whether it is a radiologic screening test such as Chest CT for lung cancer screening, screening mammography for breast cancer detection, or screening blood tests, such as PSA for prostate cancer detection. There are numerous other blood tests, with markers for numerous cancers.
Screening tests offer an opportunity for the detection of cancers at their earliest stage, thus decreasing the morbidity of cancer treatment and increasing survival. As new treatments for many types of cancer emerge, early detection becomes even more important, as new and more effective treatments are available. However, screening tests are not without cost, both in terms of monetary cost and false positive examinations, and in terms of cost for additional testing and anxiety for the patient.
The role of the medical and scientific professions of medicine and epidemiology is to determine the benefit to risk ratio, namely, is the test worth it, when and for whom? The US Preventive Services Task Force (USPSTF) has been tasked with this determination and it is now tied to mandated insurance coverage in the Affordable Care Act (ACA). Ideally, such investigations would be performed without bias as to a targeted outcome and would use only the highest quality scientific data available.
Epidemiological studies, in their purest definition, would be carried out with perfect data, in order to determine the studies with the greatest benefit/risk ratio. Even in the ideal scenario, a threshold must be drawn, so there is subjectivity to the ideal benefit/risk ratio. However, data itself can be the confounding variable. Big data is everywhere and many studies are performed which are lacking, either in the study algorithm, the quality of the equipment utilized in testing or in the population tested. Unfortunately, there may be inherent bias in the studies chosen in the determination of that benefit/risk ratio.
Recently, the USPSTF has published an initial recommendation for screening mammography for women in the 40-49 age group, with a grade of C, which does not mandate insurance coverage for screening mammography in this age group for those without risk factors. For women age 50–75, only screening every other year was given a grade of B.
In the case of screening mammography, the American College of Radiology believes that “the USPSTF limited its consideration of studies to those that underestimated the life saving benefits of mammography and greatly inflate overdiagnosis claims.” It also noted that “the USPSTF does not comply with Institute of Medicine standards, widely regarded as the medical standard.” It is widely acknowledged that, since the advent of screening mammography in the 1980’s, the mortality from breast cancer has decreased by 35 percent.
One out of 6 breast cancers occurs in women ages 40-49. Additionally, three-quarters of women diagnosed with breast cancer have no family history of breast cancer and are not considered high risk. These differing assessments by different medical/scientific entities is confusing and potentially dangerous to patients. It is uncertain whether USPSTF assessments are correct and whether the threshold for the known benefits of mammography compared to the risks of false positives and patient anxiety outweighs the risk of cancers detected later.
It is difficult for physicians to sift through this data to determine whether the correct threshold has been drawn as to whether our patients will need a screening test, and whether withholding the test could be deleterious to their health.
Recently, an acquaintance of mine was speaking to me about going through a difficult time in her life. She was just turning 40 and had personal family crises and almost did not get her first mammogram. Although she had no symptoms or family history, she went and received her first baseline mammogram. (because of the current screening guidelines for mammography)
She was diagnosed that week with breast cancer. I cannot help but say thank goodness she got her mammogram, that it was available to her and covered by insurance. Caught at an earlier stage, her chances for cure are excellent. Caught later, she would have had increased morbidity, and likely, more expensive and extensive therapy, with decreased risk of survival.
Here, epidemiology meets the individual, one that I know, and I can only hope that proper consideration is given when large entities are making decisions that affect patient lives.