Women getting fertility treatments can be reassured that in vitro fertilization (IVF) does not increase their risk of breast and gynecological cancers, according to a US study of Israeli women.
"The findings were fairly reassuring. Nothing was significantly elevated," said lead author Louise Brinton, chief of the Hormonal and Reproductive Epidemiology Branch at the National Cancer Institute in Rockville, Maryland.
Ovulation-stimulating drugs or puncturing of the ovaries to retrieve eggs can be part of IVF treatments, procedures that researchers have suspected may increase women's risk of cancer. Indeed, previous studies did link IVF early in life to heightened risks of breast cancer and borderline ovarian tumors.
But other studies have found little connection between fertility treatments and cancer.
The association has been difficult to untangle, experts say, in part because it's hard to know whether unmeasured factors not realized to IVF may affect the risk of cancer in women who have trouble conceiving. In addition, so far there haven't been a lot of women who developed cancer after fertility treatment included in studies.
"We all want answers, but it's a very difficult exposure to study, particularly when we don't have the numbers we would really like," Brinton, whose results appeared in the journal Fertility & Sterility, told Reuters Health.
She and her colleagues examined the medical records of 67,608 women who underwent IVF treatments between 1994 and 2011 and 19,795 women who sought treatment but never received IVF.
The researchers linked those files to a national cancer registry and found 1,509 of them had been diagnosed with cancer through mid-2011.
There was no difference in women's chances of being diagnosed with breast or endometrial cancer based on whether they were treated with IVF. The researchers did find that a woman's risk of ovarian cancer slightly increased the more rounds of treatment she received, but that finding could have been due to chance.
Brinton said her study was too small conclusively link IVF and ovarian cancer - and that it remained very rare, with 45 cases in the entire study.
A similar association was found in a study headed by Bengt Kallen, director of the Tornblad Institute at Lund University, Sweden, who said that any increased ovarian cancer risk might be due to the dysfunctional ovaries themselves.
"Infertile women have a primary problem with their ovaries and IVF has nothing to do with it," Kallen told Reuters Health. "It's a rather difficult thing to disentangle if there is an effect from the hormones or from the IVF procedure."
Others warned of biases that may make the results of studies like this difficult to interpret, nothing that women undergoing IVF are watched very closely, which would likely increase the chance that ovarian cancers are detected.
"You have to be extraordinarily cautious about this kind of a study," said Sherman Silber of the Infertility Center of St. Louis. "If anything. It's reassuring. One doesn't see any real increase in cancer."