乳癌治療薬（Tamoxifen）による乳癌患者の排卵誘発

乳癌治療薬のtamoxifenは排卵誘発効果のある合成ホルモン剤としても知られている。コーネル大学の研究者は、乳癌患者で将来の妊娠のために胚凍結を希望する女性にtamoxifenで卵巣を刺激し採卵を試みたところ、対照群よりも多くの胚を凍結できたという。さらに一名の女性に２個の胚移植を行ったところ双胎妊娠が成立したという。

Breast Cancer Drug Could Treat Infertility
Jan 8, 2003
By Pat Hagan
LONDON (Reuters Health) - Researchers say the breast cancer drug tamoxifen may help cancer patients retain their fertility after a woman who took it to stimulate egg production gave birth to twins.
According to doctors at Cornell University in New York, this is the first recorded case of a successful pregnancy and birth arising from the use of tamoxifen as an in vitro fertilization (IVF) treatment.
In a study looking at its effectiveness as a fertility drug, researchers discovered it boosted egg production in 12 women who had survived breast cancer.
Although tamoxifen has been known to be an ovarian stimulant for the past 30 years, its use in IVF treatment has been neglected because of its success as a breast cancer therapy, according to the report.
The new findings, published in the journal Human Reproduction, suggest it could play a key role in helping breast cancer patients who want to freeze embryos because they risk ovarian failure due to the toxic effects of chemotherapy.
"Sometimes the best ideas are the obvious ones and tamoxifen seemed the obvious choice of drug to test, although to my knowledge no one has tried it before in breast cancer patients," lead researcher Professor Kutluk Oktay said in a statement.
"We hypothesized that tamoxifen stimulation would result in higher numbers of embryos compared with natural cycle IVF, while theoretically shielding breast cancer cells against estrogen." Many doctors are reluctant to use traditional methods to stimulate the ovaries of breast cancer patients to produce more eggs, for fear that the drugs could trigger cancer growth.
Tamoxifen was originally developed back in the mid-1960s as a contraceptive before finding favor in Europe as an ovarian stimulant. But after its anti-cancer properties were discovered in 1976, its use as a fertility aid declined.
Oktay, from the Center for Reproductive Medicine and Infertility at Cornell's Weill Medical College, said the study arose from a desire to find a safe way of preserving fertility among the 15% of breast cancer patients who are still of reproductive age when diagnosed with the disease.
Even if their fertility survives chemotherapy, many of these women can simply run out of time to have a child because they are advised to wait up to five years before trying to conceive.
"These women can try natural cycle IVF without ovarian stimulation, but typically, no more than a single embryo can be achieved for immediate use or freezing," said Oktay. "So we need to find a safe way of increasing the number of embryos."
Twelve breast cancer patients were given 40 to 60 milligrams of tamoxifen for seven days, starting two or three days into their menstrual cycle, and monitored for egg production.
To gauge the effects, researchers compared them with a group of five cancer patients who had undergone natural cycle IVF.
The results showed the women taking tamoxifen produced an average of 1.6 mature eggs compared to 0.7 in the non-tamoxifen group, or control group. All 12 then went on to generate embryos to freeze for later attempts at pregnancy, compared to three out of the five controls. None of the women has since suffered a recurrence of their cancer.
One patient who had two embryos transferred has successfully given birth to twins, the researchers announced.
Oktay added: "We exploited tamoxifen's dual action as an ovarian stimulant and an anti-cancer agent.
"It would be especially fitting if a drug that has saved so many women's lives should also turn out to be a means of preserving their fertility."
Dr. Mark Johnson, a specialist in assisted conception at the Imperial College of Science, Technology and Medicine in London, said tamoxifen's benefits as an IVF treatment came as no big surprise. Other doctors in the UK, he said, have used the drug to stimulate the ovaries in women with polycystic ovary syndrome but this was the first documented case of a successful birth. Polycystic ovary syndrome is a condition marked by infertility, excess facial hair and obesity.
"I'm sure they are right to say that but the numbers of women who will benefit are quite small," Johnson said. "The numbers of people with breast cancer who have fertility problems are not that great."
SOURCE: Human Reproduction 2003;18:90-95.