A new finding challenges what has been considered common wisdom among doctors: The earlier you treat cancer, the better.

Researchers found no increase in the survival rate of patients whose relapsed ovarian cancer was found by screening tests before symptoms developed, and whose chemotherapy was started early, over that of patients whose cancer was found later when symptoms developed.

"The absolute benefit of that close surveillance has not been tested before, which is why this is a landmark paper," said Dr. Bradley Monk, a gynecologic oncologist at Creighton University School of Medicine in Arizona, who was not affiliated with the study.

Ovarian cancer is the fifth leading cause of cancer deaths in women in the United States. Up to 90 percent of women with ovarian cancer will relapse, according to Johns Hopkins University.

Ovarian cancer relapse can be found early by monitoring blood levels of a protein called CA125, produced by ovarian cancer cells. CA125 levels may be elevated months before symptoms appear.

The study followed 529 European women who were in complete remission from ovarian cancer , and had elevated CA125 levels at the start of the study. Half were given early chemotherapy treatment, and the other half received treatment only if symptoms appeared.

After nearly five years, there was no difference in survival rates between the groups 186 of the women who received early treatment died, and 184 of those who received treatment after symptoms appeared died.

However, the findings may not directly apply to today's U.S. ovarian cancer patients, Monk said.

Because the trial started in 1996, ovarian cancer treatment in the trial may not have been as modern or effective as today's options. And European protocols for cancer relapse treatment don't usually include surgery, whereas American ones do, he said.

The best message ovarian cancer survivors can take away from the study is to monitor their CA125 levels, and if they're high, to know that they have options for timing their treatment, he said.

"You just have to ask yourself, 'If you had an advanced ovarian cancer, would you like to know if it's growing out of control, or not?'" he said.

The study was published Sept. 30 in the journal The Lancet.