Women who were treated with radiation for breast cancer during the 1980s may be at an increased risk for heart disease compared with the general population, according to a new study in the March 7 Journal of the National Cancer Institute. Despite this increased risk of heart disease, radiation therapy has been previously shown to improve the chances of surviving breast cancer.
Breast cancer patients treated with radiation therapy during the 1970s are thought to have an increased risk of cardiovascular disease, but those treatment procedures are now considered obsolete. However, studies on the association between more modern radiation therapies and cardiovascular disease in breast cancer survivors have been inconclusive.
Maartje Hooning, M.D., of the Netherlands Cancer Institute in Amsterdam, and colleagues compared radiation treatment options, looking for differences in heart disease incidence among 4,414 10-year survivors of breast cancer who were treated between 1970 and 1986. Approximately half of the patients were treated for breast cancer between 1970 and 1980 and half were treated after 1980.
After a median follow-up of 18 years, the researchers identified 942 cases of cardiovascular disease, heart failure being the most common (382 out of 942). The breast cancer patients had an increase in the risk of heart attack, angina (chest pain due to an oxygen shortage in the heart), and congestive heart failure, compared with the general female population. The incidence of angina seemed to increase over time.
The researchers found differences in cardiovascular disease incidence depending on the type of treatment. Overall, patients who received radiation therapy had a greater risk of cardiovascular disease compared with those who received only surgery. In fact, the women who received only surgical treatment had a lower risk of heart attack than the general female population.
To examine the effects of changes in radiation therapy techniques over time, the researchers compared cardiovascular disease incidence in patients who were treated before and after 1980, when a new therapy to conserve breast tissue was introduced. From 1970 to 1979, patients who received radiation therapy had nearly 1.5 times the heart disease risk of patients who did not receive radiation. That rate fell to 1.35 (and was not statistically significant) for patients treated between 1980 and 1986.
The region of the body that received radiation influenced the risk of heart disease as well. For the period from 1970 to 1979, women who had radiation therapy to either the left or right side of the area between the ribs and the breastbone had an increased risk of heart attacks as well as congestive heart failure compared with patients who received little or no radiation to the heart. After 1980, patients treated with radiation to the same area had an increased risk for congestive heart failure, but not heart attacks.
The researchers were surprised to find that smoking had an unexpectedly large effect on the risk of heart disease. "We found that the joint associations between radiotherapy and smoking and [heart attack] risk were greater than expected when individual risks were summed. Consequently, the advice to stop smoking appears to be even more important for irradiated patients and should be given at the time of treatment," the authors write.
An accompanying editorial by Sharon Giordano, M.D., and Gabriel Hortobagyi, M.D., of the M.D. Anderson Cancer Center in Houston, points out another surprising finding. A certain type of chemotherapy treatment, known as CMF, was associated with a greater risk of congestive heart failure among patients in the study. "Although anthracycline-based chemotherapy is known to cause congestive heart failure, heart failure is not an expected outcome for patients who were treated with CMF chemotherapy. "This association could represent a long-term toxicity of which we were previously unaware, or, as noted by the authors, could possibly be related to induction of menopause," the authors write. "More plausibly, it could be either a spurious finding or related to residual confounding [variables] because all patients who received chemotherapy were also treated with radiation."
Article: Hooning MJ, Botma A, Aleman BMP, Baaijens MHA, Bartlelink H, et al. Long-Term Risk of Cardiovascular Disease in 10-Year Survivors of Breast Cancer. J Natl Cancer Inst 2007; 99: 365-375
Editorial: Giordano SH, Hortobagyi GN. Local Recurrence or Cardiovascular Disease: Pay Now or Pay Later. J Natl Cancer Inst 2007; 99: 340-341
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