The Science of Screening Tests
The Washington Post recently reported that the US Preventive Services Task Force has issued another finding, this one about screening for ovarian cancer (http://www.washingtonpost.com/national/health-science/ovarian-cancer-scr...). Excerpts:
A federal government task force recommended Monday that women not get routinely screened for ovarian cancer because doing so can put them at increased risk for unnecessary harm, such as major surgery.
The U.S. Preventive Services Task Force, an independent group of national experts, said it continues to discourage screening in women at average risk for ovarian cancer, which has the highest mortality rate of all types of gynecological cancer and is the fifth-leading cause of cancer death among women.
Half the women in the study were screened with transvaginal ultrasounds and a blood test called CA-125, which is how screening is typically done. The other half of the women were not screened. There were 78,216 women in this trial.
“It made no difference in the outcome,” she said.
But a high percentage of women who undergo screening experience false-positive tests that then require invasive testing, such as major surgery to open up the abdomen and take out the ovary, she said.
“That puts those women at increased risk for being harmed. That’s major surgery.”
A physician comment made on the Washington Post website:
This isn't about politics, but rather about statistics. Pap Smears are great and save a lot of lives. So it would seem logical to do the same thing for breast cancer, prostate cancer, ovarian cancer and lung cancer, all of which have available screening tests. I had a PSA in 2003, when a lot less was known. It was 4.1, 0.1 above normal. Of course I wanted a biopsy to see if I had cancer, and I did. Then I, of course, wanted that cancer out of me quickly so I had a prostatectomy. Very common complications are incontinence and impotence and a few will die from any major surgery. To boil the statistics down and make them simple 45 men have to be permanently maimed with prostatectomies to save one life because the vast majority of prostate cancers are not fatal. Is it worth it? The U.S. Preventative Services Task Force says No and I agree. The only way to stop all this is to follow the current recommendation of not doing screening PSAs on those with no risk factors. Some day a good screening test for lethal prostate cancer may be developed and when it is it should be used. The PSA is not a useful test.
For breast cancer there was much political furor a few years ago when the Task Force changed its recommendations from screening every year to every two years, beginning at age 50 rather than 40. But well over 1000 mammograms have to be done in the 40 to 50 age group, along with hundreds of biopsies of suspicious lesions, to save one life. Again is it worth it? And humans are not machines that will keep coming back time after time to undergo biopsies that do not show cancer. After two or three many will just refuse further biopsies, just as they are moving into their 50s, where the risks are much higher, and how many lives will be lost that way, counteracting the occasional life saved with earlier and more frequent screening? And like prostate cancer many breast cancers will never become life-threatening.
Cervical and breast cancers do not require deep and invasive procedures to access the lesions for biopsy. That is not true for ovarian and lung cancers. So the question really is how many times would a patient be willing to undergo deeply invasive procedures in the chest or abdomen just to find out that the suspicious lesion seen on a screening test turns out not to be a cancer? And how many will suffer major complications from such procedures? If inexpensive non-invasive tests were available that could distinguish reliably between benign benign and malignant life-threatening lesions of the breast, prostate, ovary and lung then they would be recommended for everyone. At the present time they just don't exist.
And for cervical cancer, the one major success story in cancer screening, the recommendations are changing dramatically toward less frequent screening because of testing that can be done concurrently with Pap Smears for the presence or absence of human papilloma virus (HPV) that causes most such cancers.
The recommendations of the US Preventive Services Task Force about screening for prostate cancer and breast cancer were greeted with anger by some and skepticism by many. It seems that any advice which might curtail access to any medical intervention is viewed with hostility, almost paranoia. Many of the comments on the Washington Post website about this report were openly vicious towards the US Preventive Services Task Force, stating or implying that its members are mere stooges in the control of health care delivery being arranged by the Obama administration. This despite the fact that all professional organizations with an interest in the control of ovarian cancer agree with the Task Force on this issue: routine screening for ovarian cancer should not be done. The physician comment quoted from the WP website is a voice of reason. Cancer screening, which seems like such a logical, useful thing, is not as simple as the concept makes it sound. The gold standard for cancer screening is and should be whether the screening program actually makes a difference in disease specific mortality. Clearly, ovarian cancer deaths occur just as commonly in the screened and unscreened populations. We know this because a large trial of the screening test has been done, comparing the results in two randomly selected populations. Why should public dollars be used to pay for a screening test, and the resulting invasive medical interventions, when there is no clinical science to support the use of the screening test?
The major problem in US health care delivery is cost. American health care costs are roughly twice the average on a per capita basis of other first world countries. The reason is wasted money on inefficient health care financing (due to the inadequacies of the private health insurance business model) and poor quality, including paying for inappropriate care, meaning care not supported by clinical science. Americans need to stop fuming about paranoid delusions that some government agency is trying to kill them in order to save money on health care costs and start realizing that the real risk of unnecessary disease and death in our health care system is found in the use of invasive interventions where clinical science finds no possible benefit.
The Utah Healthcare Initiative proposes that Utah's health system be improved by organizing a mechanism for using public health care funding only for medical interventions which are proven by clinical science to be a benefit. For details, please click on the "Solutions" tab found on the Utah Healthcare Initiative website.
Dr. Joe Jarvis