Monday, May 18, 2009
Screening Tests for Cancer often Wrong
A study has been published in the Archives of Internal Medicine that shows there is a high incidence of "false-positive" tests when adults undergo the usual screening tests for cancer.
Keep in mind that these are not tests that are done to diagnose specific symptoms or concerns, but the tests that are part of health maintenance and screening.
The researchers found that for men receiving these tests: chest X-ray, flexible sigmoidoscopy, digital rectal exam and serum prostate-specific antigen (PSA), the false positive rate (no cancer) after undergoing all four exams for 3 years was 60.4%. Of these men, 28.5% would go on to have an invasive procedure.
For women the false positive rate was 48.8% for these tests: CA-125, transvaginal sonograms, Chest X-ray and flexible sigmoidoscopy. 22.1% of these women would undergo an invasive procedure to further work up the false abnormality.
They did not include mammograms for women, but they calculated that after 3 examinations the incidence of a false positive rate would be 18%.
I found these results rather surprising and there are some important facts here. First of all, we do not recommend screening chest X-rays (for lung cancer) or Ca-125 tests (for ovarian cancer) for these very reasons. They are not good screening tools and are not specific enough to give us valid information that saves lives. The key word here is SCREENING. If a patient has symptoms or genetic risk factors, that changes the decision of which tests to use.
The ability to detect cancer early and cure it has been advanced by the recommended screening tools. This is why doctors harp on patients to get these tests at the recommended ages. Patients often think we can detect all forms of cancer early with tests and that, unfortunately, is not the case. But mammography, colonoscopy and pap tests are proven to save lives.
It is important, however, to know that all tests come with a risk of false positives and the need to do further testing, sometimes invasive, to determine if it is really cancer or just a benign abnormality that will not affect the patient's health.
Posted by Toni Brayer, MD at 7:35 AM