In general, getting screened for cancer seems like the responsible thing to do, since preventing the disease is always better than treating it once it takes hold. But the latest research shows that screening women for ovarian cancer does not reduce women’s risk of dying from the disease.
As cancer goes, ovarian cancer is not common. An estimated 177,000 American women are currently living with the disease and 1.4% of women can expect to be diagnosed with ovarian cancer during their lifetime. But because ovarian cancer is typically not diagnosed until it has advanced and spread to other parts of the body, it is among the deadliest cancers in women, with only 30% of women surviving five years after diagnosis. Nearly 14,000 women die from ovarian cancer each year. Earlier diagnosis and treatment of the disease could potentially help improve women’s chance of survival.
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In the new trial involving more than 78,000 women aged 55 to 74, some were randomly assigned to undergo two types of ovarian cancer screening, a blood test once a year for six years along with an ultrasound annually for four years; the remainder did not get screened. The participants were then monitored for about 13 years for ovarian cancer.
At the end of the trial, researchers found, both groups had about the same chance of dying from the disease. Screening also did not help detect tumors at earlier stages. What’s more, 6%, or 3,285 women who were screened had false-positive results leading to unnecessary invasive procedures, including surgery to remove one or both ovaries; 15% of those who had screening-related oophorectomies suffered major complications.
The study’s lead author, Dr. Christine Berg, chief of the early detection research group at the National Cancer Institute, says the results highlight the fact that broad-based screening may not always be useful for cancer. At least in the case of ovarian cancer, widespread screening using current methods appears not to be useful.
At the moment, the best tests for picking up tumors in and around the ovaries include a blood test for a marker known as CA-125, which is expressed on ovarian cancers (as well as by other tissues), and an ultrasound of the tissue to identify potentially malignant lesions. In the current study, about 77% of all tumors found in the two groups were advanced — Stage 3 or Stage 4.
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“That was very disappointing,” says Berg of the fact that the screening failed to detect tumors at earlier stages. When ovarian cancer is discovered before it has spread beyond the ovary, some 90% of patients survive five years. “That indicates that we really have to have a better understanding of the biology of ovarian cancer,” she says.
Most ovarian cancers originate on the surface of the ovary, but there is emerging evidence that some tumors may begin in the neighboring fallopian tubes, which connect the ovaries with the uterus. Both the ovaries and the fallopian tubes have openings into the abdomen, and it may be possible that cancerous cells also break off and seed tumors in the abdominal cavity. It may be that both the CA-125 and ultrasound tests are picking up tumors only after they have reached the abdomen. “We’ve got to get a diagnostic or blood test that can detect growths when they are sill extremely small, and before any cells break off,” says Berg. “And that’s a real challenge.”
The new findings suggest that existing ovarian-cancer screening methods will not help women if used more widely. Only 2% to 3% of healthy women are now screened for ovarian cancer with the CA-125 test; that percentage may be slightly higher among women with a history of breast cancer or who have the BRCA1 or BRCA2 gene mutations, which have been linked to a higher risk of ovarian cancer. Expanding screening beyond that population may lead to too many false-positive results without a benefit in survival.
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In women who have previously been diagnosed with ovarian cancer, doctors currently use CA-125 to monitor their treatment — tracking changes in the cancer marker helps determine whether the disease is getting worse. The new results, says Berg, don’t shed much light on the usefulness of the tests in these women, but an ongoing study in the U.K. might. In that trial, women with elevated levels of CA125 are getting more frequent blood tests to see whether the variations in marker levels correlate with an increased risk of disease or disease progression.