The risk of death from heart disease caused by radiation therapy for breast
cancer has declined steadily over the past 25 years, according to a new study.
Journal of the National Cancer Institute, March 16, 2005 (see abstract of journal article).
About four out of every 10 women with breast cancer in the United States
receive adjuvant (additional)
radiation therapy
after surgery. Studies have
shown that giving radiation after
lumpectomy
reduces by two-thirds a woman's
risk that her cancer will recur in the same breast. Survival rates for women
treated with lumpectomy and radiation are the same as for women who have a
mastectomy.
Radiation may also be recommended after a mastectomy to reduce the
risk of cancer recurrence.
Observational studies
suggest that radiation therapy is underused in breast
cancer patients, in part because of concerns about its adverse effects. In
particular, several studies have shown that women treated with radiation have a
higher risk of death from heart disease. These studies mostly involved patients
treated in the 1960s and 1970s. Since that time, however, new techniques for
giving radiation therapy have allowed doctors to minimize the radiation dose to
the heart.
Radiation therapy to the left breast may deliver a higher dose of radiation to
the heart than radiation therapy to the right breast. Previous studies have
shown higher death rates from heart disease in women treated with radiation for
cancer in the left breast than in those who received radiation to the right
breast.
The current study was conducted to find out whether breast cancer patients'
risk of death from heart disease caused by radiation therapy had changed over
time.
Researchers analyzed information about more than 27,000 women who were
diagnosed with breast cancer between 1973 and 1989 and were treated with
radiation therapy in addition to surgery. The information was obtained from the
National Cancer Institute (NCI's)
Surveillance, Epidemiology, and End Results
program.
The investigators grouped the women according to when their cancer was
diagnosed and whether it was in the left or right breast. They then calculated
death rates from heart disease both for the entire study population and for the
subgroups.
The study's lead author is Sharon H. Giordano, M.D., MPH, of the University of
Texas M.D. Anderson Cancer Center in Houston.
In total, 8.7 percent of women with left-sided cancers died of heart disease
within 15 years of their breast cancer diagnosis, compared with 7.5 percent of
women with right-sided cancers. This difference was so small that it was not
statistically significant - that is, it could have occurred by chance.
The overall death rate from heart disease among study participants declined
steadily over the period of time covered by the study. The additional risk for
women with left-sided cancers also fell steadily, dropping by six percent per
year between 1979 and 1988. Among women diagnosed in 1988, death rates from
heart disease were the same for women with left-sided and right-sided cancers.
The researchers counted deaths from heart disease that occurred within 12 to 15
years of a breast cancer diagnosis. However, previous studies have shown that
the risk of death from heart disease caused by radiation therapy persists for
at least 20 years, points out Jack Cuzick, Ph.D., of Cancer Research UK in
London, England, in an accompanying editorial. Longer
follow-up
is needed to
show definitively whether or not radiation therapy still increases the risk of
death from heart disease.
Also, the recent trend toward diagnosing more breast cancers early could have
affected the study's findings, the authors note. Women whose cancer was
detected before it had spread to the
lymph nodes
may have received less
extensive radiation therapy and, for that reason, had a lower risk of heart
disease.
"This is a well-done study which shows that the careful application of modern
radiotherapy techniques reduces the risk of heart complications," says C.
Norman Coleman, M.D., associate director of the radiation research program of
the National Cancer Institute. "As with all studies of long-term outcome,
additional follow-up data are important. These results mean that the decision
to use or not use radiation as part of breast cancer therapy can be based on
the clinical and biological features of the patient's disease and not on the
fear of inducing a heart complication."
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