Ovarian cancer can be hard to track because it spreads more diffusely through the body than other types of cancers that often grow as solid tumors. The standard method for tracking ovarian cancer and measuring how well the cancer is responding to treatment has been to use CT scans, ultrasounds, or other imaging techniques. However, a new report from researchers in Denmark suggests that, at least in later-stage ovarian cancer, a blood test may be more a more accurate measure of whether the cancer is growing or shrinking.

What the researchers wanted to know: Do imaging techniques or blood tests better measure the progress of late-stage ovarian cancer?

What they did: Women with ovarian cancer who were registered in the Copenhagen Database for Ovarian Carcinoma were included in the study if they had later-stage ovarian cancer, were tested with both imaging and blood screening, and had been treated at least twice with specific, commonly used chemotherapy drugs. Sixty-eight patients in the registry fulfilled the inclusion criteria. The scientists analyzed the results of imaging scans and blood tests done on each woman after her second round of chemotherapy. Specifically, they looked at a blood test that measures the levels of a substance called cancer antigen 125 (CA-125); 90 percent of women with ovarian cancer have high levels of this antigen. The researchers followed women who had both of these tests for several years to see which better predicted their chance of survival.

What they found: Using the CA-125 blood test to measure the response of the cancer to therapy was a better way to predict how long the women would survive than the imaging scans. When women who had been through several rounds of chemotherapy had both of these tests done, a blood test showing decreased levels of CA-125 better predicted whether the women would live longer than imaging scans showing a decrease in tumor size.

What it means to you: This study argues for the use of blood tests instead of imaging scans, which are what an international panel of cancer experts recommends. Both can be good tools, but the blood test is much cheaper and less time consuming. However, levels of CA-125 can be elevated for other reasons than ovarian cancer, for example pregnancy, so it is more often used in postmenopausal women and as a marker for treatment rather than as a diagnostic tool. Also, some women with ovarian cancer don't have elevated levels of CA-125.

Caveats: These women were all treated with a specific chemotherapy regimen, paclitaxel and platinum compound in the first round and topotecan and paclitaxel in the second round. Because the therapy used can skew the blood test results, this study may not apply to women treated with a different regimen. In addition, a reduction in CA-125 levels does not always mean that tumors have shrunk and thus may not be a reliable predictor of the cancer's remission all the time.

Find out more: The National Ovarian Cancer Coalition has information about ovarian cancer, including how it is detected.

For more information about CA-125, check out the Mayo Clinic's explanation.

Read the articles: Gronlund, B. et al. "Should CA-125 Response Criteria Be Preferred to Response Evaluation Criteria in Solid Tumors (RECIST) for Prognostication During Second-Line Chemotherapy of Ovarian Carcinoma?" Journal of Clinical Oncology. Oct. 15, 2004, Vol. 22, No. 20, pp. TK

Rustin, G.J.S. et al. "Can We Now Agree to Use the Same Definition to Measure Response According to CA-125?" Journal of Clinical Oncology. Oct. 15, 2004, Vol. 22, No. 20, pp. TK

Abstracts online: Gronlund: http://www.jco.org/cgi/content/abstract/JCO.2004.10.028v1

Rustin: http://www.jco.org/cgi/reprint/JCO.2004.06.628v1 (full text)