Researchers at Yale School of Medicine have succeeded in identifying, characterizing and cloning ovarian cancer stem cells.

In fact, the research team headed by Gil Mor, M.D., associate professor in the Department of Obstetrics, Gynecology & Reproductive Sciences at Yale School of Medicine, has also demonstrated that these stem cells are the reason behind ovarian cancer's recurrence and resistance to chemotherapy.

"These results bring us closer to more effective and targeted treatment for epithelial ovarian cancer, one of the most lethal forms of cancer," said Mor.

Cancerous tumors comprise of both cancerous and non-cancerous cells and the cancerous cells have a further subclass called cancer stem cells, which has the capability of replicating indefinitely.

"Present chemotherapy modalities eliminate the bulk of the tumor cells, but cannot eliminate a core of these cancer stem cells that have a high capacity for renewal. Identification of these cells, as we have done here, is the first step in the development of therapeutic modalities," said Mor.

For the study, the researchers isolated cells from 80 human samples of either peritoneal fluid or solid tumors. They also identified cancer stem cells that were positive for traditional cancer stem cell markers including CD44 and MyD88. These cells also showed a high capacity for repair and self-renewal.

The isolated cells almost always formed tumors, in which 10 percent of the cells were positive for cancer stem cell marker CD44, while 90 percent were CD44 negative.

The researchers could isolate and clone the ovarian cancer stem cells and found these cells to be highly resistant to conventional chemotherapy while the non-cancer stem cells responded to treatment.

"Isolating and cloning these cells will lead to development of new treatments to target and eliminate the cancer stem cells and hopefully prevent recurrence," said Mor.

The findings of the study were presented recently at the annual meeting of the American Association for Cancer Research (AACR) Meeting in San Diego, California.