Infant monkey BRENDA was born from transplanted ovarian tissue. Credit: Oregon Health & Science University

Conventional cancer treatments such as chemotherapy and radiation often carry one lasting side effect: sterility. But recent advances offer some hope in preserving the fertility of young female cancer patients.

Belgian researchers reported in June that, for the first time, a woman had become pregnant after receiving transplanted ovarian tissue. The results were presented at the annual meeting of the European Society for Human Reproduction and Embryology.

“If this was indeed a pregnancy that resulted from frozen grafted tissue, then it is an amazing accomplishment,” says David Lee, assistant professor of obstetrics and gynecology at the Oregon Health & Science University in Portland. “It is the ultimate proof of principle—this validates what many people have been working on for many years.”

Many in vitro fertilization clinics routinely freeze embryos. In the US, about ten clinics also freeze the oocytes or eggs. Worldwide, nearly 200 pregnancies have resulted from frozen eggs.

Freezing ovarian tissue offers one alternative that could be used any time a medical treatment might harm ovaries, says Kutluk Oktay, associate professor of obstetrics and gynecology at Weill Cornell Medical College in New York. In March, Otkay and his colleagues reported that they had used the method to restore fertility in a breast cancer survivor (Lancet 363, 837–840; 2004).

Three months after transplantation, the ovarian tissue began to produce hormones and eggs. In the eight months following, Oktay collected 20 eggs, 8 of which looked healthy enough to fertilize in vitro. Of the resulting two embryos, only one was genetically normal. Oktay transferred that embryo to the woman's uterus when it reached the four-cell stage, but the woman did not become pregnant.

Lee and his colleagues have had more success with a similar technique in monkeys. To simulate the loss of fertility and the changes in hormone production in women battling cancer, the researchers removed the ovaries of seven anesthetized female monkeys.

They transplanted some of each monkey's own ovarian tissue back into its body and monitored hormone production and the development of follicles—cavities in the ovarian tissue where the eggs develop. Within a few months, the monkeys' hormone cycles resumed and they began producing eggs.

The eggs were fertilized through intracytoplasmic sperm injection and the resulting embryos transferred to surrogate monkey mothers. Following the normal five-month monkey gestation period, a healthy female infant was born (Nature 428, 137–138; 2004).

The next step would be to try this procedure using frozen ovarian tissue, says Lee.

Most techniques used to safeguard the fertility of cancer patients are relatively new and in need of refinement, but there is a great need for such techniques, says Lynn Westphal, director of Stanford University's oocyte donor program. “Since cancer survivors are doing much better and living longer lives,” she says, “this is much more of an issue than it was in the past.”