What you need to know about health screening tests
By Michael Rabovsky, M.D.
Recently, during her annual “well woman” exam, Mary, a healthy 50-year-old schoolteacher, asked me about screening her for ovarian cancer.
Tragically, one of Mary’s friends recently died from ovarian cancer. Mary has no risk factors for ovarian cancer and no family history of ovarian cancer or other cancers. I explained to Mary that, unfortunately, there are no reliable screening tools to diagnose ovarian cancer.
We went on to have a discussion about screening and the characteristics of reliable medical screening tests. The purpose of screening is to identify an unrecognized disease or condition in people who feel well and have no symptoms.
Screening tests should be applied to those conditions that meet the following criteria:
1. Consider the treatment options. Acceptable methods of treatment must be available.
2. Look at the impact of the illness. The disease or condition must have a significant effect on the quality of life and life expectancy.
3. Determine whether treating asymptomatic disease will help. The disease must have a period during which there are no symptoms, when detection and treatment will significantly reduce illness and/or death. Furthermore, treatment in this asymptomatic phase must yield a therapeutic result superior to that obtained by delaying treatment until symptoms appear.
4. The disease incidence must be high. The incidence, or the number of new cases identified, must be significant to justify the cost of screening to a population of people.
5. Screening must be easy to do. The screening tests must be simple to perform, simple to interpret and relatively comfortable to people.
6. The costs must be reasonable. The tests must be available at a reasonable cost. This not only applies to the monetary cost of performing the tests, but also to the evaluation of false positive tests, the psychological impact on a person of a false-positive test, and consideration of the medical risk incurred in performing the test as well as further testing required in the workup of a positive test.
Ovarian cancer screening: Why you may not need it
Ovarian cancer is the leading cause of gynecologic cancer deaths in the United States. Approximately 22,000 U.S. cases of ovarian cancer are diagnosed annually, with 14,000 deaths each year.
If diagnosed in an earlier stage, the five-year survival rate (the percentage of people alive five years after diagnosis) can be as high as 90 percent. The five-year survival rate drops to 25 percent if the diagnosis is made at a later stage.
The goal of screening would, therefore, be to diagnose ovarian cancer in its earlier stages, when treatment would have a beneficial effect on outcomes. Several tests have been used to screen for ovarian cancer. But three large studies failed to show that screening resulted in earlier diagnosis of ovarian cancer.
So, although there is evidence to show that diagnosing ovarian cancer at its earlier asymptomatic stages leads to better survival, there have been no tests shown to detect ovarian cancer in these earlier stages.
Furthermore, positive tests for ovarian cancer generally lead to surgical procedures. One study revealed that 15 percent of women undergoing a surgical procedure for a false-positive screen experienced a serious complication related to the surgery.
So I explained to Mary that not only was there no evidence that screening led to better outcomes, but that with the tests currently available to diagnose ovarian cancer, screening could lead to significantly more potential harm than good.
Colorectal cancer screening: Why you need it
In contrast, colorectal cancer is a condition that meets the aforementioned screening criteria.
Most colorectal cancers develop slowly over several years; before a cancer develops, a growth of tissue or tumor usually begins as a noncancerous polyp on the inner lining of the colon or rectum.
A polyp is a benign, noncancerous tumor. Some polyps can progress into a cancer but not all do. There are generally no symptoms associated with polyps. When a precancerous polyp is identified by a screening test, progression to cancer is prevented, and there is no effect on health or life expectancy.
However, when colorectal cancer is diagnosed after symptoms develop, the five-year survival rate can range from 6 percent to 74 percent, depending on the stage of the cancer at the time of diagnosis.
Colon cancer affects a significant number of people, there are acceptable screening methods and treatments, and identifying and treating precancerous or early-stage cancer in the asymptomatic period leads to better outcomes.
Because it meets screening criteria and the incidence of colorectal cancer starts to increase at age 50, I recommended that Mary get screened.
Other critical screening tests
In addition to screening for colorectal cancer, I also advised Mary to be screened for breast cancer, with an annual mammogram, and for cervical cancer, with a Pap smear, and HPV, or human papillomatous virus, test every five years. We reviewed the warning signs of skin cancer, as well, and I also counseled Mary to have a blood test, to check her lipid profile, and a fasting blood sugar test as a screen for diabetes.
The message here is that screening recommendations vary, and it’s important to discuss the appropriate screening tests with your doctor.
(WhatDoctorsKnow is a magazine devoted to up–to–the minute information on health issues from physicians, major hospitals and clinics, universities and health care agencies across the U.S. Online at www.whatdoctorsknow.com.)
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