Early detection and treatment can improve the prognosis of most cancers. Certain screening tests have been developed to help with early detection, such as mammograms for breast cancer and colonoscopies for colon cancer. However, for some cancers, like ovarian cancer, effective screening tests are unknown. The symptoms of ovarian cancer will often only occur in later stages and can easily be confused for more benign problems. As a result, about 70% of ovarian cancer cases are not found until the cancer has already spread and the possibility of a cure is remote.
The Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial was designed to examine the effectiveness of established and potential cancer screening tests. This portion of the study was focused on the use transvaginal ultrasound and a blood test called CA 125 to screen for ovarian cancer. The study, published in Obstetrics and Gynecology, found that the tests were more likely to create false positives than to find early ovarian cancer.
The ovarian cancer portion of the study included 34,261 healthy women 55-74 years of age. The women all received four annual screenings. One half of the group received usual gynecological care. The other half of the group also had CA 125 and transvaginal ultrasounds done every year. Of the women that had the transvaginal and CA 125, 3,388 women (10%) had one or more positive screening tests. Of these women 1,170 (35%) had biopsies done to confirm the presence of cancer. In only 60 cases (5%) did the biopsies show invasive cancer of the ovary or nearby tissue. Furthermore, 72% of the cancers that were found were already late stage on diagnosis. Study results published earlier showed that out of the 570 women that had surgery after a positive screening test, 541 had no evidence of cancer.
Screening tests are not perfect and can give false positive and false negative results. A false positive means the test indicated a disease was present when there was in fact no disease. A positive predictive value (PPV) helps to determine how accurate the results are. In this case, over the four years of the study, the PPV for the transvaginal ultrasound and CA 125 was 1%-1.3%. This means that out of all the positive tests, cancer was actually present in only about 1% of the cases.
Doctors often use test results as a tool to help them reach a diagnosis, but the two tests examined here appear to be more stressful than successful. A false cancer diagnosis can cause a significant amount of distress for the person diagnosed and can lead to unnecessary, invasive procedures like biopsies. Screening for ovarian cancer has yet to come of age.
Although a reliable screening test for ovarian cancer remains unavailable, it is still worthwhile to see your primary care doctor and gynecologist on a regular basis. Screening tests for breast and cervical cancer (mammography and Pap smears, respectively) as well as other health conditions have been shown to the lower the risk of death. Although an effective screening test for ovarian cancer will have to wait, there is some comfort in knowing that it is a relatively rare condition in the general population. However, if you have a family history of ovarian or breast cancer—particularly in young, first-degree relatives (mother or sister)—your personal risk of these cancers could be considerably higher. If this is the case, you may wish to speak with your doctor about the possibility of genetic testing.
American Cancer Society
American Congress of Obstetricians and Gynecologists
Gynecologic Cancer Foundation
Buys SS, Patridge E, Greene MH, et al. Ovarian cancer screening in the Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial: findings from the initial screen of a randomized trial.Am J Obstet Gynecol. 2005 Dec;193(6):2183-4.
Partridge E, Kreimer AR, Greenlee RT, et al. Results from four rounds of ovarian cancer screening in a randomized trial.Obstet Gynecol.2009 Apr;113(4):775-82.
Last reviewed June 2009 by Richard Glickman-Simon, MD