Transvaginal ultrasound and CA-125 are not reliable or accurate enough for early-stage ovarian cancer

Gynecologic surgeon Dennis Chi discusses why screening for ovarian cancer is not as widespread as it is for certain other cancers.  Dr. Chi is Deputy Chief of the Gynecology Service, Director of the Fellowship Program for the Gynecology Service, and Co-Director of Pelvic Reconstructive Surgery in Memorial Sloan Kettering’s Department of Surgery.

Ovarian cancer is the tenth most common cancer found in women, and the fifth most common cause of cancer death (2013). Only about 15 percent of ovarian cancers are detected at the earliest stage, when the cancer is still confined to the ovary and the disease is most likely to be curable.

For other cancers, including cancers of the breast, cervix, prostate, and colon and rectum, widespread screening approaches have been introduced and shown to increase the likelihood that these diseases are detected at an early stage. And a draft recommendation from a government advisory panel in late July stated that people who are at high risk for lung cancer should receive annual low-dose CT scans.

Yet finding reliable screening methods for early-stage ovarian cancer has been challenging. Memorial Sloan Kettering gynecologic surgeon Dennis Chi explains why.

Unreliable Tests

Dr. Chi says one reason that women of average risk are not screened for ovarian cancer is that current tests are not reliable or accurate enough, especially for early-stage disease.

Transvaginal ultrasound, in which an ultrasound probe is inserted into the vagina to allow a radiologist or technician to view the organs in the pelvic region, has been shown in studies to be a promising imaging method for routine screening of ovarian cancer.

Yet many early-stage cancers are not detected by transvaginal ultrasound, and the rate of false positives — abnormalities that upon further investigation are shown not to be cancer — is very high.

Another test that is currently in use is a blood test for the serum marker CA-125. This protein is elevated in 90 percent of advanced ovarian cancers, but only in 50 percent of patients with stage I cancer. “For early-stage disease, it’s essentially no better than a coin flip,” Dr. Chi says.

Invasive Biopsies

If a woman is found to have an abnormality in a blood test or an ultrasound, performing a biopsy is more invasive than tests done when abnormalities are found on a mammogram or a Pap smear, Dr. Chi notes. “A needle biopsy of the breast or a colposcopy of the cervix can be done as a relatively simple office procedure,” he explains. “For a potential ovarian cancer, a major surgical procedure called a laparoscopy is required.”

Taking a biopsy of the ovary can lead to future infertility and other problems. “In addition,” Dr. Chi explains, “if you biopsy part of the ovary and it does contain cancer, you run the risk of spilling the cancer cells and spreading the cancer. Yet we don’t want to remove the entire ovary when the likelihood is high it does not contain cancer.”

For women who are at high risk of ovarian cancer because of mutations in the BRCA1 or BRCA2 genes or other family history, guidelines established by a team of Memorial Sloan Kettering experts do recommend such screenings, but for women in the general population, whose risk of ovarian cancer is about one in 70, Dr. Chi and others believe the risks greatly outweigh the potential benefits.

A Focus on Early Detection

There is currently much research focused on ways to better detect ovarian cancer at an early stage. Many centers, including Memorial Sloan Kettering, are looking for biomarkers in the blood that are more accurate than CA-125 at indicating early-stage disease or even precancerous conditions.

Additionally, research in recent years has shed light on the possible origins of ovarian cancer. “Many studies have suggested that ovarian cancers may start in the fallopian tubes rather than the ovaries,” Dr. Chi explains. “If this hypothesis proves to be correct, it may allow us to develop better imaging methods and more-accurate screening tests.”

“One of the reasons it’s so hard to detect ovarian cancer at an early stage is because ovaries are inside your body where small lumps cannot be felt,” Dr. Chi says. Common symptoms of the disease — such as nausea, pelvic pressure, urinary or gastrointestinal symptoms, or pain — can be caused by many conditions that are not ovarian cancer.

“If you’ve had several of these symptoms together for a duration of time greater than a few months, it’s probably a good idea to see your gynecologist,” he concludes. “He or she may recommend an ultrasound or a CA-125 test or possibly a CT scan.”