Nov. 9, 1999 (Atlanta) -- Women who receive fertility drugs with in vitro fertilization (IVF) are not more likely to develop cancers of the breast or ovary five to 10 years after treatment, according to a study in the Nov. 6, 1999, issue of the journal The Lancet. Researchers say the results should be reassuring, although, additional follow-up is needed.
Fertility drugs and their link to cancers have been studied in the past due to the fact that they overstimulate the ovaries and expose women to very high levels of estrogen, which is thought to increase cancer risk. Previous studies have essentially discounted any link between fertility drugs and breast or uterine cancer. However, studies have shown conflicting results regarding the link between these drugs and ovarian cancer with some research showing no link and others showing an increase in more aggressive ovarian tumors in women who have received fertility drugs.
In a study of nearly 30,000 women, the largest of its type thus far, researchers compared the incidence of cancer in IVF patients with the general population. Women who received one or more treatment cycles with fertility drugs were included in the study.
Although more women were diagnosed with breast and uterine cancer within a year after receiving IVF treatment, the chances of acquiring cancer over a five to ten year period were comparable between those that received IVF and those who did not. Allison Venn, PhD, the chief investigator and epidemiologist with La Trobe University in Victoria, Australia, tells WebMD there are possible explanations. "Either the diagnoses were made early because these women were being followed so closely or the IVF drugs somehow promoted the development of preexisting cancers."
The impact of fertility drugs on cancer has been the subject of American research as well. In response to the Australian study, scientists at the University of Washington commented that the findings must be considered along with the limitations, although, "the results should be reassuring to IVF patients who underwent three cycles [of treatment] or less," says Janet Daling, PhD, professor of epidemiology at the University of Washington, Seattle. "In our study, we found a higher incidence of cancer among women who underwent 12 cycles or more."
Daling says that more historical information would help to interpret the data as well. "Patients often receive fertility drugs long before they are referred for IVF and that's critical for interpreting the results. Previous pregnancies and oral contraceptive use is important as well. Of course, most women [who] develop breast, ovarian, and uterine cancers [develop it] later in life, so ongoing follow-up may yield more definitive results."
In fact, the Australians are currently planning just that. "We've made a case for following these women well into the future and there seems to be support for such a project," says Venn. Of the research conducted at the University of Washington, Venn sees little application for IVF protocols in Australia. "The reality is that women in this country don't often undergo as many cycles; three or so is the norm here and most women aren't treated with fertility drugs outside of IVF. It's also important to remember that not every cycle even requires fertility drugs; often there are frozen embryos from previous cycles held in reserve."
Venn says one finding does require further explanation. "We noted that women whose infertility was not linked to a specific cause had an increased incidence of ovarian and uterine cancer whether or not they received infertility drugs. In some of these women, infertility may actually have been a ... symptom of an underlying cancer. It's definitely an area for further study."