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NEW YORK (Reuters Health) - Fertility treatment drugs may not be tied to an increased risk of developing cancer, suggests a new study of more than 24,000 Swedish women treated with in vitro fertilization (IVF).
Some prior studies had hinted at a link between fertility drug use and the development of breast, uterine and ovarian cancers, but the numbers of women followed in these studies were small, lead researcher Dr. Bengt Kallen of the University of Lund, in Sweden, noted in an email to Reuters Health.
To investigate further, Kallen and his colleagues used health registries in Sweden to identify a larger group of about 24,000 women who delivered a baby following IVF treatment performed between 1982 and 2006.
They compared the rates of cancer among these women and 1.4 million other women in the general Swedish population who had also given birth during the same time period.
The researchers found that less than 2 percent of women in the IVF group developed one or more cancers after treatment (during an average follow-up of 8 years). Nearly 5 percent of women who did not undergo IVF before giving birth later developed cancer, report the researchers in the journal Human Reproduction.
After accounting for the mother's age, number of previous children and smoking, the researchers found that the overall risk of a woman developing cancer after IVF was about a quarter lower than among women who had not undergone the treatment.
"A couple who needs IVF does not have to be afraid that the hormone treatment used -- at least those used in Sweden -- will carry a risk for the woman to develop cancer," Kallen told Reuters Health.
While the risk of ovarian cancer alone was more than double after IVF compared to untreated women, the researchers note that this was an improvement on the nearly 4-fold increased risk seen among these women before they received IVF.
Kallen suggested that this relationship is probably explained by abnormalities in ovarian function, which both increase the risk for infertility -- and therefore the need for IVF -- and the risk for cancer.
"The risk for two common cancers, breast and cervical, was significantly lower than expected," Kallen said.
Kallen also offered two possible explanations for these surprising findings: the selection of women who got IVF may have been healthier than the other women or, perhaps more likely, IVF-treated women may undergo more mammography and cervical smears, which can lead to earlier detection and treatment of precancerous conditions.
Of note, the only fertility drugs currently used with IVF in Sweden are gonadotropins, hormones that are used to stimulate the ovaries. Prior to the mid-1990s, these drugs were used in combination with another treatment, clomiphene.
Gonadotropins are also the primary fertility hormones prescribed today in IVF clinics across the U.S. Clomiphene may still be enlisted, but only in very rare cases, Dr. Helen Kim, Director of the In Vitro Fertilization Program at The University of Chicago, told Reuters Health.
Despite some concern regarding the relatively homogenous population of Sweden, in contrast to a country as ethnically diverse as the U.S., Kim still noted that the findings should be fairly generalizable.
SOURCE: link.reuters.com/jyh38q Human Reproduction, online November 18, 2010.