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 Nearly 10,000 women who received drugs to stimulate
ovulation were no more likely to develop breast cancer during 30
years of follow-up than those who never used the drugs, researchers
report.
Lead author Louise Brinton, chief of the Hormonal and Reproductive
Epidemiology Branch at the National Cancer Institute in Bethesda,
Maryland, said the findings are reassuring.
Previous studies have raised concerns over the drugs because women
are exposed to higher levels of estrogen during fertility
treatments. Extended exposure to extra estrogen could increase the
risk of breast cancer.
"The other worry is that (these drugs) cause increased ovulation and
. . . that could be linked to an increase in breast cancer risk,"
Brinton told Reuters Health.
For the new study, the researchers analyzed records for 9,892 U.S.
women who were followed for some 30 years after having been
evaluated for infertility between 1965 and 1988.
About 38 percent of the study participants were exposed to the
fertility drug clomiphene and about 10 percent were exposed to drugs
known as gonadotropins.
Over the three decades of follow-up, 749 breast cancers were
diagnosed among the study participants.
Overall, women who were exposed to either type of fertility drug
were no more likely to develop breast cancer than those who didn't
use the medicines to stimulate ovulation.
The researchers did find an increased risk of breast cancer among a
small subset of women who were prescribed the highest doses of
clomiphene, however.
Current practice limits treatment with the drug to just three to six
cycles. But women who were exposed to 12 or more cycles of
clomiphene treatment had a 70 percent higher risk of developing
breast cancer compared to women not exposed.
Also, women who took gonadotrophins, usually in combination with
clomiphene, but were still never able to become pregnant were about
twice as likely to develop breast cancer.
Some of that increased risk may be the result of whatever underlying
problem caused those women's persistent infertility, the researchers
speculate.
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For the small group of women who took clomiphene for more than a
year, the reasons for the increased risk are less clear, the authors
conclude in their report, published in Cancer Epidemiology,
Biomarkers & Prevention.
"It's reassuring that if women desire pregnancy and unfortunately
have infertility that they can undergo treatment without
modification of their overall risk for cancer later," Dr. Kurt
Barnhart, president of the Society for Reproductive Endocrinology
and Infertility, told Reuters Health.
Barnhart, who was not involved in the new study, is based at the
Perelman School of Medicine at the University of Pennsylvania in
Philadelphia.
It's important to note that the new study shouldn't change how women
are screened for cancer in any way, he added.
The researchers also caution that continued study of women who
receive fertility treatments is needed, because many women included
in the current study were still fairly young (in their early 50s) by
the end of the follow-up, so they had not reached the age range when
breast cancer diagnoses are most common.
"We'll be looking at other results as they emerge and keeping our
eye on IVF (in vitro fertilization), which is the more common
treatment nowadays," Brinton said. ___
Source: http://bit.ly/1dS3oqO
Cancer Epidemiology, Biomarkers & Prevention, online April 3, 2014.
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