Researchers led by Dr. Toshiyasu Taniguchi of the Fred Hutchinson Cancer Research Center said they've identified a new mechanism that explains why some recurrent ovarian tumors become resistant to treatment with commonly used platinum-based chemotherapy drugs such as cisplatin and carboplatin.

The findings were based on the study of ovarian-cancer cells from women with inherited mutations in the BRCA2 gene.

However, Taniguchi said, "Because BRCA1 and BRCA2 have similar functions in terms of DNA repair, we may be able to generalize these findings for women with either mutation."

While ovarian tumors initially respond very well to platinum-based chemotherapy, eventually between 70 percent and 80 percent of advanced-stage ovarian-cancer patients develop a resistance to these drugs.

"The majority of advanced-stage ovarian-cancer patients die due to acquired resistance to platinum-based drugs," said Taniguchi. "It is a serious problem."

The study that included scientists from the University of Washington, Cedars-Sinai Medical Center and the Mayo Clinic is described in the online issue of the journal Nature.