Women who receive radiation therapy as part of their treatment for very early breast cancer do not have an elevated risk of developing or dying from cardiovascular disease later in life, new data suggest.
In a population-based cohort study, researchers assessed cardiovascular outcomes among 10,468 women in the Netherlands given a diagnosis of ductal carcinoma in situ (DCIS) before the age of 75 years during 1989-2004.
Overall, 28% of the cohort received radiation therapy after their surgery (lumpectomy or mastectomy), lead investigator Naomi B. Boekel reported in a press briefing held in advance of the breast cancer symposium sponsored by the American Society of Clinical Oncology, where the findings will be presented in full.
During a median follow-up of 10 years, about 9% of the patients received a diagnosis of cardiovascular disease.
There was no significant difference in the rate between patients who did vs. did not receive radiation, or between patients who received left-sided radiation (in which the heart gets a low direct dose) vs. right-sided radiation (in which the heart gets only a scatter dose).
Specifically, the rate of cardiovascular disease diagnosis was 9% in patients who received surgery alone, compared with 8% in patients who received surgery plus radiation, a nonsignificant difference. The CVD rate was 7% in patients who received left-sided radiation therapy vs. 8% in their counterparts who received right-sided radiation therapy, another nonsignificant difference.
Furthermore, DCIS survivors as a whole had a 23% lower risk of dying from cardiovascular disease, compared with peers in the general Dutch population.
"This lower risk might be due to lifestyle adaption after DCIS diagnosis," proposed Ms. Boekel, a doctoral student at the Netherlands Cancer Institute in Amsterdam. "It could be due to conflicting risk factors between DCIS and cardiovascular disease, such as age at menopause. Or it could also be due to differences in health consciousness in that DCIS patients are probably more health conscious than the general population."
The risk of all-cause mortality was essentially the same between the DCIS cohort and the general population.
"We also looked at this for specific cardiovascular diseases and there were similar results, so there is no risk difference between these treatment groups," Ms. Boekel reported.
"Although these results are reassuring, longer follow-up is necessary before definitive conclusions can be drawn," she commented.
There is no established upper limit for such follow-up, she said. "But other studies have shown that the increased risk of cardiovascular disease starts after 5 to 10 years. ... We do have half of the cohort at more than 10 years, but [estimates] are less precise. So we need another 5 to 10 years before we are sure."
Strengths of the study, according to Dr. Steven O’Day, director of clinical research at the Beverly Hills (Calif.) Cancer Institute and moderator of the press briefing, included its occurrence in a time period in which more modern radiation therapy techniques were used. Also, the follow-up was fairly lengthy, although he agreed that more is needed.
"This is an important study that allows us to feel comfortable continuing our aggressive treatment of DCIS, with screening and trying to reduce overall mortality from breast cancer," Dr. O’Day maintained.
Ms. Boekel disclosed no relevant conflicts of interest. Dr. O’Day disclosed no relevant conflicts of interest.