Molecule may reveal ovarian cancer

Scientists trying to find warning signs of ovarian cancer have identified several proteins that sometimes turn up loud and clear in the early stages of this cancer. Unfortunately, they don’t appear consistently, so the search for more such markers continues.

In the Oct. 3 Journal of the National Cancer Institute, researchers report that blood from ovarian cancer patients harbored nearly double the amount of a protein called prostasin that blood from similarly aged women free of cancer had.

Samuel C. Mok, a molecular biologist at Brigham and Women’s Hospital in Boston, and his colleagues used so-called microarray technology to find genes that are especially active in ovarian-tumor cells. They found 30 such genes and zeroed in on a few that encode certain kinds of proteins with known links to cancer, including prostasin.

Luckily, other scientists already had identified an antibody to prostasin. So Mok and his colleagues used this antibody to test blood from 64 ovarian cancer patients and 137 women free of cancer. The team noted how often the antibody bound to its target. The results revealed that the cancer patients had prostasin concentrations of 13.7 micrograms per milliliter of serum, the clear, protein-rich component of blood. The women without cancer averaged only 7.5 g/ml.

Ovarian cancer patients also had higher prostasin concentrations before their ovaries were removed than after. This suggests that the tumor cells produce the substance, Mok says.

A protein called CA 125 is currently the best marker for ovarian cancer. However, since some women have the cancer but do not have elevated concentrations of CA 125, this protein is an imperfect signpost by itself. Similarly, “prostasin alone is not ready for prime time,” says Sudhir Srivastava, a molecular biologist at the National Cancer Institute in Rockville, Md. But combining a CA 125 test with one for prostasin and possibly for other markers could increase the accuracy of ovarian cancer screening and catch more cancers earlier when they are still treatable, he says.

A woman getting surgery and other treatment for ovarian cancer that hasn’t spread has a 90 percent likelihood of surviving 5 years after diagnosis. In most women, however, the cancer is found only after it has spread outside the ovaries. Only 28 percent of these women live more than 5 years after diagnosis.