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."