Hormone Replacement Therapy And Breast Cancer
by Patricia T. Kelly, Ph. D.
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 hormone replacement therapy.
When differences are not significant, an increase in
risk may well be due to other factors, not the one being studied, such as
hormone replacement therapy 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 hormone replacement therapy 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 hormone replacement therapy 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 hormone replacement therapy 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
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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.
ABOUT THE AUTHOR
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.
