Mice that received ovary tissue grafts from women with malignant lymph systems didn't go on to develop cancers, according to the report, which appears in the October issue of the journal Human Reproduction. Although not an unequivocal testament to their safety, experts who perform the transplants say the findings are reassuring and bode well for future studies of the procedures.
Transplant surgery is intended to restore fertility to women made sterile by cancer treatments or other therapy, as well as those who undergo premature menopause. It may also help delay the onset of menopause, easing its symptoms and allowing older women to get pregnant.Every year, experts estimate, between 40,000 and 50,000 American women of childbearing age undergo cancer therapies that strip them of the ability to conceive. And many women in North America and elsewhere have had their ovarian tissue frozen while they undergo sterilizing treatment for cancer and other conditions.
Scientists have shown that they can graft egg-producing ovarian tissue onto the pelvic wall of infertile women. But that site is more difficult to harvest eggs from than is the forearm, which is also easier to monitor for egg development. The operation on the arm is also somewhat less complicated than that involving the pelvis.
Although both techniques might preserve a cancer patient's fertility, earlier research has suggested that the transplanted ovarian tissue may "re-infect" her with tumors.
In the new study, an international research team led by Dr. S. Samuel Kim of the University of Washington in Seattle grafted ovary tissue from 18 cancer patients into 30 diabetic and severely immune-suppressed mice. Thirteen of the women had Hodgkin's disease and five had more serious non-Hodgkin's lymphoma, both of which are cancers of the lymph system. Three additional mice received a graft of cancerous lymph tissue from the women.
After up to four months, the mice were autopsied, and none was found to be carrying signs of human cancer, the researchers say. However, all three animals who got the cancerous lymph tissue had developed lymphomas that were determined by genetic testing to be human in origin.
"Our patients were deliberately selected for having high-risk disease and in the three years following tissue harvesting, half have died of lymphoma," Kim says in a statement. "So the study was based on worst-case scenarios of highly aggressive lymphomas that were likely to have already spread at the time the ovarian tissue was harvested."
"It looks like with Hodgkin's disease in particular, it's a safe thing to do. But we don't know about breast cancer and leukemia," says Roger Gosden, a McGill University fertility research and a co-author of the latest study.
Gosden, a pioneer in the field of ovary tissue transplants, says safety is still a significant concern. And although it's possible to preserve a woman's eggs for later use, some disease treatments may do irreparable harm to her reproductive organs and leave her unable to conceive, he adds.
Dr. Kutluk Oktay, a fertility expert at Cornell University's Weill Medical College who has performed ovarian transplants, calls the latest work "reassuring, because it shows the risk [of new cancer] is nonexistent or very, very small." Performing such a study in humans would be extremely difficult because of ethical issues, adds Oktay.
Oktay says the results are particularly comforting in light of his plans to conduct a large study, on as many as 40 women, in which he will graft their own ovarian tissue into their forearms to create a safe repository of eggs during cancer therapy or other treatments of their pelvis.
Oktay and his colleagues described two patients who successfully underwent this procedure in an article published this week in the Journal of the American Medical Association.