P.Mean: Controversies with a test for ovarian cancer (created 2008-08-27).

A recent article in the New York Times,

raises some interesting questions about diagnostic testing.

The article describes OvaSure, a test developed to detect ovarian cancer.

The need for such a test is immense. When ovarian cancer is detected at its earliest stage, when it is still confined to the ovaries, more than 90 percent of women will live at least five years, according to the American Cancer Society. But only about 20 percent of cases are detected that early. If the cancer is detected in its latest stages, after it has spread, only about 30 percent of women survive five years.

Another concern about this test is that it will produce too many false positives.

The biggest concern is not that the test will miss cancers but that it will say a cancer is there when it is not. That would then subject women to needless surgery to have their ovaries removed. Dr. Berchuck of Duke said only 1 of 3,000 women has ovarian cancer. So even if a screening test had a 1 percent rate of false positives, it would mean that 30 out of 3,000 women tested might be subject to unnecessary surgery for every one real case of cancer.

One concern is that the test has not been evaluated in an appropriate population.

In a study published in the journal Clinical Cancer Research in February, the test correctly classified 221 of 224 blood samples taken from women with ovarian cancer or from controls. It identified 95 percent of the cancers, and its false positive rate — detecting a cancer that was not there — was 0.6 percent. But Dr. Beth Y. Karlan, director of the Women’s Cancer Research Institute at Cedars-Sinai Medical Center in Los Angeles, said the samples tested were not representative of what might be encountered in routine screening. There were very few blood samples from women with early stages of the most deadly type of ovarian cancer. “That’s really what we want to find,” she said.

Another concern about this test is that it will produce too many false positives.

The biggest concern is not that the test will miss cancers but that it will say a cancer is there when it is not. That would then subject women to needless surgery to have their ovaries removed. Dr. Berchuck of Duke said only 1 of 3,000 women has ovarian cancer. So even if a screening test had a 1 percent rate of false positives, it would mean that 30 out of 3,000 women tested might be subject to unnecessary surgery for every one real case of cancer.

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