Understanding Ovarian Cancer Screening Results from the PLCO Trial

At the 2006 SGO Annual Meeting on Women’s Cancers™ results from the ovarian cancer screening arm of the Prostate, Lung, Colon and Ovarian (PLCO) trial were presented.  Researchers reported new criteria that allowed for the detection of 87% of early ovarian cancers and 93% of advanced ovarian cancers in asymptomatic postmenopausal women who participated in the study.

The PLCO trial is a randomized trial in which subjects are assigned to usual medical care versus annual screening for Prostate, Lung, Colon and Ovarian cancer.  In this clinical trial, over 28,000 women, ages 55 – 74, were screened for ovarian cancer using a transvaginal ultrasound and serum CA 125 test.  

The study results provoke an obvious question for women:   Should I have an annual ultrasound and CA 125 test?  In this brief communication we will attempt to guide women and their families in answering this question.

Ovarian cancer screening is difficult.  The main difficulties arise because ovarian cancer is relatively uncommon.  Roughly one in seventy women will be affected during their lifetime.  At any point in time there are few cases in an asymptomatic population.  With low prevalence diseases like ovarian cancer, a positive test is more likely to be a false alarm rather than a true warning of disease. 

A second problem with ovarian cancer is that there is no safe and simple means to sort out false positive screening results from true positive results.  Surgical removal of the ovaries is the only sure way to find out if a positive test means that you have ovarian cancer or if it’s a false alarm.  So if an inaccurate test causes too many women to have unnecessary surgery, the test may cause more bad health effects than it prevents.

The researchers involved in the PLCO trial are still watching and measuring to determine the gains and losses that occurred as a result of the screening tests performed in this trial.   They are also still watching what’s happening in the group that is not being screened.  Ultimately they will be able to provide high quality information to guide the debate as to whether any of the screening methods used in this trial saved lives and were “worth it” in terms of financial costs and overall health.  From the ovarian cancer screening portion of the trial one downside is already clear.  More than 500 women underwent surgery to remove one or both ovaries as a result of abnormal screening results in this trial, and only 20 cases of ovarian cancer were diagnosed among these women.  In the future, these numbers may improve as researchers employ new guidelines for interpretation of CA 125 and ultrasound results.  However, even women who are able to avoid surgery will suffer considerable worry as a result of false positive tests.

Physician members of the Gynecologic Cancer Foundation recommend that ovarian cancer screening continue to be evaluated in the context of clinical trials.  We await final analyses from the PLCO and other trials, and we continue to hope for a better, non-invasive diagnostic test when screening abnormalities are detected.  Women with a positive family history of breast or ovarian cancer, and women with known mutations in the cancer associated BRCA1 and BRCA2 genes should speak with a knowledgeable specialist about cancer screening.  For average risk women we recommend continued monitoring of this debate and further education about risks, prevention, signs and symptoms of gynecologic cancers.  Log on to the Women’s Cancer Network at www.WCN.org for more information and for an assessment of your individual risk for gynecologic cancers.

March 24, 2006