ST. LOUIS -- When Joy Lagos learned she had cancer, she was confident she would beat it. What brought the San Francisco resident to tears, however, was knowing that radiation and chemotherapy would lead to early menopause and rob her of the chance to have children.

Last week, that may have changed.

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A renowned infertility expert in suburban St. Louis transplanted a whole ovary from Lagos' sister into Lagos, a step that could enable her to have children. Dr. Sherman Silber completed the transplant Feb. 5, after performing the same procedure between twins last month.

The operations are believed to the first whole-ovary transplants ever done in the United States. Surgeons in China reported a successful transplant earlier this decade, but offered scant details.

The surgery could restore normal hormone function for women going through early menopause, whether because of cancer treatments or other, unexplained causes. It also could mean that one day, a woman with cancer could freeze an ovary, undergo chemotherapy and radiation, and have her own ovary returned later to restore her fertility.

Lagos, 30, is now waiting to see whether the transplant takes hold and allows her to ovulate normally, and whether she can get pregnant. The twins are also waiting to learn the outcome of their operation.

When Lagos was diagnosed with non-Hodgkins lymphoma in 2004, her older sister Maeapple Chaney, now 31, donated bone marrow. Lagos was cured of cancer, but the treatment disabled her ovaries and she went into early menopause.

"I was devastated," Lagos recalled, her voice breaking as she tried to talk about it Monday. Now married, Lagos was not with a partner at the time, and so was not able to freeze any embryos, she said.

After the cancer treatment, she wanted to have children of her own. But also, the menopause also induced osteoporosis, diminished her sex drive, and interfered with the natural "ebb and flow" of her emotions, she said.

"I think it sounds selfish, but I just wanted to feel like a woman again," she said.

Chaney was willing to donate eggs so that Lagos and her new husband, Rodrigo Lagos, could have a baby through in vitro fertilization, but then Rodrigo Lagos saw a TV report about Silber.

In 2004, Silber placed strips of ovarian tissue from a fertile twin into her prematurely menopausal sister. That woman, Stephanie Yarber, has since given birth to two children. The doctor has since done similar surgeries on six other sets of twins, all of them involving transplants of ovarian tissue, not whole ovaries.