Researchers who carried out the study said that most treatments increase the long-term risk of cardiovascular disease.
"Most breast cancer therapies today - including new treatments still under development - increase long-term risk of cardiovascular disease," said Lee W. Jones, Ph.D., an exercise physiologist and assistant professor in the Department of Surgery at Duke University Medical Center, Durham, NC.
"We don't know exactly how large the added risk is, but we believe it's substantial. Recent gains in breast-cancer-specific survival could be markedly diminished by an increase in the long-term risk of cardiovascular death," he added.
The researchers point out that many middle-aged and older women who are diagnosed with breast cancer already have age-related risk factors for cardiovascular disease, such as high blood pressure.
In addition, physical inactivity and obesity have been linked to both breast cancer and heart disease. This pre-existing risk only heightens the likelihood that breast cancer therapies will harm the cardiovascular system.
Cancer therapies damage the heart and blood vessels in a variety of ways.
Conventional chemotherapeutic agents silently injure the heart muscle in as many as half of patients, diminishing the heart's pumping ability and increasing the risk of heart failure years later.
Radiation therapy can cause scarring and tissue damage in the heart and lungs.
Herceptin, a monoclonal antibody used in treating women with high-risk genetic profiles, is also associated with cardiac toxicity and heart failure.
Experimental therapies that limit the growth of blood vessels in tumours can cause abnormal blood clotting, high blood pressure and reduced cardiac function.
Even hormone therapy with aromatase inhibitors raises concern, given the long-term reduction in estrogen levels. Equally important, many women become physically inactive during cancer therapy, resulting in significant weight gain.
The researchers said that keeping heart health in mind during breast cancer therapy can be as simple as performing a baseline evaluation of standard cardiovascular risk factors including age, blood pressure, cholesterol levels, smoking history and body weight.
Therefore, depending on the results, the patient may need a prescription or a referral to a cardiologist.
Exercise is an important component of any treatment program. Even during cancer therapy, exercise will likely help a woman feel better.
Dr. Jones is now conducting research to determine whether exercise improves blood flow to the tumour, thereby enhancing delivery of cancer drugs to their intended target.
The new research is published in the October 9, 2007, issue of the Journal of the American College of Cardiology.