Do Antidepressants Increase Breast Cancer Risk?
New Research Raises More Questions
By Dianne Partie Lange, RN
WebMD Medical News
June 16, 2000 -- Ever since some studies in animals showed that
antidepressants might increase the risk of breast tumors,
researchers have been looking for a similar link in humans. Now a
group of Canadian researchers reports that its study of more than
5,000 women found that those who had taken the drugs for at least
two months had a greater probability of having breast cancer than
those who had not.
This finding, which the researchers discussed at a meeting of the
Society for Epidemiologic Research in Seattle, adds support to a
study done by the same researchers published this spring in the
American Journal of Epidemiology. That study looked at a much
smaller number of women. In it, researcher Nancy Kreiger and her
colleagues at the University of Toronto reported that women who took
an older class of drugs, called tricyclic antidepressants, for two
years had twice the risk of breast cancer. And those taking Paxil,
one of a class of drugs called serotonin reuptake inhibitors
(SSRIs), had seven times the risk. But because of the small number
of patients in that study, the true effect of the drugs couldn't be
In the more recent study, a substantially smaller link was seen
between antidepressants and breast cancer.
"The reason we looked at this is that a psychiatrist, who is also
one of the co-investigators, noticed that in mouse studies,
antidepressants may cause mammary tumors," one of the researchers,
Michelle Cotterchio, PhD., tells WebMD.
"The results could be the result of chance alone. That's why
future studies need to be done. It takes five to 10 studies in
different subgroups before people start believing the findings."
Indeed, several critics have pointed out what they consider to be
shortcomings in the studies, or problems in the interpretation of
The animal studies were prompted by the recognition that the
antidepressant drug molecule is similar to that of other chemicals
that are known to cause cancer. These agents appear to inhibit an
enzyme associated with cancer, explains Judith Parsells Kelly, PhD.
The next step was to do so-called epidemiologic studies, in
which the incidence of cancer in women who had used antidepressants
was compared with that in those who hadn't used the medications.
"Epidemiology is really a rather crude tool, and it's effective
for identifying increases in risk when the magnitude of the risk is
quite high," Kelly says. But that is not the case with
antidepressants and breast cancer. Kelly was not involved in the
Canadian study, but she has studied links between drugs such as
SSRIs, tricyclic antidepressants, and antihistamines and cancer.
Several physicians who spoke to WebMD raised the question of
whether depression alone could have been responsible for the
increased risk Krieger and colleagues found.
"There's a general theory that depression may make people
susceptible to cancers in general, because it can decrease immune
function. There has not been any strong data to support that. On the
other hand, it hasn't been looked at in a well-designed study," says
Bruce Trock, PhD, associate professor of medicine and oncology at
Georgetown University School of Medicine in Washington.
Krieger's findings raise other several questions, Trock says,
such as: How does the number of women who took antidepressants and
didn't get cancer compare to the general population? Were the
researchers able to eliminate the impact of known breast-cancer risk
For these reasons, more studies need to be done. At this point,
Kelly says, "Women should not avoid taking antidepressants because
they're afraid of developing breast cancer. The evidence is not
strong enough to justify that type of action."
Says Charles Loprinzi, MD, an oncologist at the Mayo Clinic in
Rochester, Minn., who has studied the use of Prozac to relieve hot
flashes in breast cancer survivors: "The bottom line must be that
you can't put much credence in [these findings]. The numbers are
small and consistent with what might have occurred by chance. This
is the same sort of risk that people have talked about with alcohol
use. It's very, very small indeed."
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