Tiny ovarian tumors lurk in the Fallopian tubes for an average of four years before they grow large enough to be detected, researchers reported on Monday in a study that explains why diagnosis usually comes too late to save a woman's life.

They said they were trying to find ways to improve testing for the cancer, one of the deadliest because it is so hard to detect before it has spread.

Reliable early detection would save so many more lives than many new blockbuster anticancer drugs, Howard Hughes Medical Institute researcher Dr. Patrick Brown of Stanford University in California, who led the study, said in a statement.

There is a long window of opportunity for potentially life-saving early detection of this disease, but the tumor spreads while it is still much too small to be detected by any of the tests that have been developed or proposed to date.

Ovarian cancer kills 140,000 women every year globally and 15,000 in the United States alone. Genetic mutations are known to raise the risk, but most patients do not have a clear genetic risk, and no good screening test exists.

Blood tests for a compound called CA-125 may help guide therapy but cannot tell a doctor and a patient if a seemingly healthy woman has a tumor.

Brown's team analyzed tumors discovered in women who had their Fallopian tubes and ovaries removed because they had a high family and genetic risk of ovarian cancer.

They found little tumors that had not been detected in many of the women -- most less than 3 millimeters across, smaller than a small peppercorn -- they reported in the online Public Library of Science journal PLoS Medicine >here

We are miles away from detecting the most deadly ovarian tumors at this early stage, but now we have a chance of actually designing an effective test that will allow us to treat them before they become deadly, Brown said.

New imaging methods that can detect such a tiny tumor might be one way to go, or perhaps finding compounds produced only by the tumors that could be detected in the blood or in a vaginal swab.

California Medicine Cancer