HAMBURG, Germany—Radiotherapy for breast cancer increases the risk of death from cardiovascular disease (CVD), compared with patients who did not receive such treatment, according to data from a large retrospective cohort study. Maartje Hooning, MD, a clinical epidemiologist from the Netherlands Cancer Institute, Amsterdam, and lead investigator of this study, presented the findings at the 4th European Breast Cancer Conference (abstract 291).
Dr. Hooning’s research team studied data from 7,247 patients with early breast cancer, who ranged from 17 to 71 years of age. These patients had been treated for stage I-III breast cancer and had been admitted to the Netherlands Cancer Institute or the Daniel den Hoed Cancer Center in Rotterdam between 1970 and 1987. Patients have been followed for a median of 14 years, and 34% have been followed for more than 20 years. For 92% of the patients, a complete medical status was available up to January 1998.
The investigators compared mortality from cardiovascular disease in patients receiving radiotherapy and nonirradiated patients. The study population’s cardiovascular mortality rates were than compared with those of the general female population. The team also clearly documented the sites of the radiation fields.
Compared with the general female population, the number of cardiovascular deaths in the study population was within the normal range of expectancy. Further analysis showed a 2.2-fold increase in cardiovascular deaths among patients who had received radiotherapy, compared with those who had not (range of risk, 1.4 to 3.6). "In terms of absolute excess risk, this means 12 extra cardiovascular deaths per 10,000 irradiated patients per year," Dr. Hooning said.
The nonirradiated group actually had a significantly lower cardiovascular mortality at 0.6-fold (range, 0.3 to 0.8) than the general female population, suggesting that the risk profile for breast cancer is protective against cardiovascular disease. Dr. Hooning explained this apparent anomaly by saying that a healthier life style after breast cancer may play a role.
"When you analyze the data, it is not such an unexpected development after all," Dr. Hooning said. "Breast cancer is linked with a higher socioeconomic status, which is associated with better nutrition, a lower risk of hypertension, and less obesity. So, as a result, breast cancer patients might indeed have a lower risk profile for cardiovascular disease." The diagnosis of cancer may also have led patients to improve their lifestyle. "Stopping smoking and losing weight through exercise and a healthy diet may contribute to the lower cardiovascular mortality rate," Dr. Hooning said.
The radiation-related risk increased dramatically among patients who had more than 10 years of follow-up. Patients treated before the age of 45 had an even greater radiation-related increased CVD risk [Standardized Mortality Ratio (SMR) = 2.6]. This increased risk is thought to be caused by the lower background risk of CVD in younger woman, compared with older woman.
