Cancer Research Lab

As a treatment for breast cancer, radiotherapy, even modern regimens, appears to increase the risk of cardiovascular disease, according to a report in the Journal of the National Cancer Institute for March 7.

Earlier reports have indicated that radiotherapy regimens used in the 1970s elevate cardiovascular risk, but it has been less clear if more recent regimens also increase the risk.

“Apart from the clear benefits of adjuvant radiotherapy, physicians should still be aware of the potentially increased risk of cardiovascular disease following specific radiotherapy regimens in long-term breast cancer survivors,” senior author Dr. Flora E. van Leeuwen, from the Netherlands Cancer Institute in Amsterdam, and colleagues note.

To investigate, the researchers evaluated 4414 breast cancer patients who survived for 10 years after treatment radiotherapy between 1970 and 1986. The rates of cardiovascular disease in these patients were compared with those seen in the general population.

A total of 942 cardiovascular events were logged during a median follow-up period of 18 years, yielding a standardized incidence ratio of 1.30.

Radiotherapy limited to the breast did not increase the risk of cardiovascular disease. Inclusion of the left or right internal mammary chains, however, did increase the risk.

Internal mammary chain radiation in the 1970s appeared to increase the risk of myocardial infarction and congestive heart failure by 2.55- and 1.72-fold, respectively, compared with no radiation. By contrast, radiotherapy in the 1980s did not raise the risk of myocardial infarction, but was associated with 2.66- and 3.17-fold increased risks of heart failure and valvular dysfunction, respectively.

In the 1980s, adding adjuvant chemotherapy to radiotherapy increased the risk of congestive heart failure by 1.85-fold. Moreover, a 3-fold increased risk of myocardial infarction was seen radiotherapy-treated patients who also smoked.

In a related editorial, Dr. Sharon H. Giordano and Dr. Gabriel N. Hortobagyi, from the M.D. Anderson Cancer Center in Houston, comment that the study “provides important new information on the cardiac toxicity of radiation therapy.”

They also praise the study’s methodology, calling the 18-year follow-up period “impressively long” and citing certain unique features, including evaluation of both morbidity and mortality, and comparison of toxicity by radiation fields.