Cancer screening guidelines can be confusing on their own, with different recommendations for different groups. Add on a contentious political climate around healthcare and emerging private services, and the whole process can feel overwhelming. In the United States, controversy surrounding healthcare coverage includes preventive screenings. According to an , Medicare is adding restrictions to coverage of breast ultrasound screening. Cases like this encourage us to revisit the concept of preventive screening in its full complexity.
In come private companies with a shiny solution: scans to detect for cancer, just in case you want to go beyond the cancer screening tests that your doctor recommends. Is the $2500 price tag worth it? With claims that the comprehensive MRI can detect over 500 conditions across 13 organs, it might be. But as with many too-good-to-be-true health claims, the nature of these scans is troublesome. Not only are they unregulated, but it鈥檚 possible to do more harm than good. Dr. Richard Bruno describes the concept of an in which a test uncovers a finding that necessitates more testing (often much more invasive) that would have never caused symptoms or health problems for the patient. It鈥檚 like finding a tiny scratch on your car and deciding to replace the entire bumper, even though the scratch would鈥檝e never caused a real problem.
Now, you may be thinking, 鈥榳hat鈥檚 the harm in being extra cautious?鈥� Well, screening tests are rarely 100% accurate. If a test results in a false positive, it can lead to unnecessary stress and even risky treatments. On the flip side, a false negative can result in an incorrect sense of security. The lack of complete certainty in screening can be described by a foundational concept in epidemiology: specificity and sensitivity.
Sensitivity of a test refers to the probability of having a positive test given that the disease is present.
Sensitivity = (# of people who have the disease AND a positive test) / (# of people who have the disease)
On the other hand, specificity of a test refers to the probability of having a negative test given that the disease is absent.
Specificity = (# of people who do not have the disease AND have a negative test) / (# of people who do not have the disease)
Photo from
If a test has 90% sensitivity, that means 10% of those with the disease will not have a positive screening test and consequently might face delays in diagnosis and treatment. For a specificity of 90%, that means that 10% of people are expected to have false positive and face increased stress and further testing for a disease that is not present. In a way, screening tests are like a going fishing with a net that allows some fish to escape and sometimes catches too many fish.
To illustrate the complexity of screening, consider cervical cancer. Human papillomavirus (HPV) is a virus associated with cervical cancer. Nearly all women with dangerous cervical cancer have . DNA testing and pap smears are two methods of screening for cervical cancer. The development of dangerous cervical cancer takes , so early detection via screening is a good strategy to try to catch and manage cases early. However, since many positive screening tests do not develop into full-blown cancer, testing can also lead to false positives. Researchers have observed that cervical cancer declines more in areas with better screening programs. In Canada, cervical cancer deaths have declined dramatically, likely due to widespread participation in pap smear testing starting .
Even though cervical cancer screening has been very successful but still has some risks. The pap smear test has which is great, but since a high number of females get screened, that means that 1% of positive tests will be incorrect. The slight imprecision of these tests is why it鈥檚 recommended for women to start testing in their twenties because before that age, there鈥檚 less risk for dangerous cervical cancer.
Screening tests are simply tools to identify people who don鈥檛 have symptoms but might be at risk for a health problem. They are not perfect, and a positive screening test is not a diagnosis in and of itself: it will lead to further diagnostic tests, such as a biopsy. In certain cases, population-level screening programs have been shown to reduce the number and severity of a disease, but they are not supported for all conditions. In some cases, the cost-benefit ratio is in favor of waiting until an individual has symptoms of a disease to perform comprehensive testing.
What to be done? Should you order a full-body MRI scan? No. Perform the tests that are recommended for your demographic and consult your doctor to determine screening tests you would benefit from. A great resource to consult for which screening tests to undergo is the which provides evidence-based screening recommendations for common diseases. And remember- instead of spending $2500 on an overpromising MRI, you are more likely to prevent cancer by developing healthy eating and exercise habits.
Paige is a 黑料不打烊 Masters of Science student studying Epidemiology with a focus on exercise and ovarian cancer.
Part of the OSS mandate is to foster science communication and critical thinking in our students and the public. We hope you enjoy these pieces from our聽Student Contributors聽and welcome any feedback you may have!
