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HORMONE REPLACEMENT THERAPY AND BREAST CANCER: THE
RISKS IN PERSPECTIVE
Janet M., a fifties-something woman, entered my
office and said as she sat down, "I've read that if I take hormones
I'll increase my breast cancer risk. I'm going crazy without sleep and
with these mood swings, but I don't want to increase my breast cancer
risk by taking hormones."
Like many women, Janet had heard that a recent
study, the Women's Health Initiative (WHI), definitively showed that
hormone replacement therapy (HRT) increases breast cancer risk. Janet,
like most people, didn't realize that this study found no statistically
significant increase in breast cancer risk to women who took HRT.
When differences are not significant, an increase
in risk may well be due to other factors, not the one being studied,
such as HRT use. As often happens when a medical story is reported, the
emphasis was on the increase in risk, not whether the increase was
likely to be due to the agent being studied or to the size of the risk.
The actual size of a risk is important in any
woman's decision making process. In this case the risk was exceedingly
small -- only 8 in 10,000 women a year -- which is 0.08% or eight
hundredths of one percent! Janet was amazed to learn the actual size of
the increase, and said, "You mean I was getting all concerned for a
risk that small!"
"And," I pointed out, "even this very small
difference in risk may not be due to hormone use." I explained that
breast cancers take an average of eight years to reach about half an
inch in size. This means that breast cancers started in the first year
of the study would not be detected for eight or more years. The study
followed women for only about five years, so all or most of the breast
cancers found were probably present in an undetected state before the
study began.
Janet asked if HRT use might have caused some
breast cancers to grow more rapidly and therefore be detected sooner
than eight years. This is unlikely. A number of studies find that
breast cancers in women who were using HRT were not larger and were not
dividing more rapidly than breast cancers in non hormone users. Since
breast cancers grow more slowly in older women and the average age in
this study was 63, breast cancers in this group would tend to grow more
slowly and so take even longer than the eight year average to be
detected.
Women in the WHI study used a particular type of
hormone Prempro. The results of this study therefore do not apply to
other, newer approaches in which more natural hormones are used and a
woman's menstrual cycle is more closely approximated.
Janet was surprised to learn that many studies
find that women who use HRT do not have an increase in breast cancer
risk compared to women who don't use hormones, even when hormones are
used for twenty years. Also, in another large study in which some women
were assigned to take Prempro and others not, women who used Prempro
had no significant increase in breast cancer risk.
As Janet left, she said, "I can see now that when
I hear about a study I need to know how big a risk is and not just that
it is increased. I'll also ask how long a study it was. This discussion
has given me a whole different perspective."
Understand and manage your cancer risk. Visit http://www.ptkelly.com
and sign up for our free teleforum.
Patricia T. Kelly, Ph.D. is a medical geneticist
who specializes in providing information about cancer risk to
individuals and health professionals. She is affiliated with Saint
Francis Memorial Hospital in San Francisco. Information about her book,
Assess Your True Risk of Breast Cancer, can be found on her web site: http://www.ptkelly.com.
Dr. Kelly is a medical geneticist who has been a
Diplomate of the American Board of Medical Genetics since 1982. In 1993
she became a Founding Fellow of the American College of Medical
Genetics. She received her Ph.D. in genetics from the University of
California, Berkeley. | 