BOSTON – Here’s heartening news that physicians can convey to breast cancer survivors: Modern breast irradiation did not appear to cause late-term cardiac toxicity in a study that examined women a quarter of a century after they were treated.

Investigators found no significant differences in Framingham Heart Study risk scores, hemodynamic parameters, pericardial thickening, or heart failure among 50 women who had been randomized in the 1970s and 1980s to either mastectomy or breast-conserving surgery (BCS) and radiation, Dr. Charles B. Simone II reported at the annual meeting of the American Society for Radiation Oncology.

Although the survival rate was slightly lower among patients treated with breast-conserving therapy, the difference does not appear to be related to radiation dose to the heart, said Dr. Simone of the Hospital of the University of Pennsylvania in Philadelphia. There were no differences in survival among women treated with BCS and radiation to left- or right-sided tumors.

"Based on this study, in the era of 3D planning, patients with early-stage breast cancer treated with radiotherapy do not have a higher risk of long-term cardiac morbidity compared with patients having mastectomy," he said.

The patients studied included 50 of 102 survivors from an original cohort of 237 women who had participated in the National Cancer Institute’s Breast Conservation Trial (79-C-0111), with randomization from 1979 to 1986. In that trial, women with stage I or II breast cancer received modified radical mastectomy with axillary node dissection or they underwent lumpectomy plus node dissection and a radiation dose of 45-50.4 Gy to the whole breast; the latter came with or without treatment of regional nodes, followed by a boost of 15-20 Gy with either iridium 192 brachytherapy or electrons.

All node-positive patients underwent 6-11 cycles of chemotherapy with doxorubicin and cyclophosphamide, and beginning in 1985 postmenopausal women with positive nodes were given tamoxifen.

The trial was unique at the time in that it used CT simulations for treatment planning and dose inhomogeneity corrections, Dr. Simone noted.

Diverging Survival Curves

At a median of 25.7 years after randomization, 43.8% of mastectomy patients were still alive, compared with 37.9% of BCS patients. Although the difference was not significant, it appeared to represent a divergence of survival curves that had been virtually identical for the first 25 years.

The trend could not be accounted for by secondary malignancies, changes in distant metastasis, or any other breast cancer–related causes, leading the investigators to question whether it might be due to radiation toxicity to the heart, as some studies have suggested.

In all, 26 patients who had had BCS and 24 who underwent mastectomy agreed to come back for the cardiac toxicity study.

The investigators took a detailed cardiac history, and subjected the women to exams, cardiac labs, cardiac MRI with a 3 Tesla magnet to look for anatomic and functional abnormalities, and CT angiogram to look for stenotic coronary disease and determine coronary arterial calcium score (CAC) of atherosclerotic burden.

They also looked at radiation technique parameters such as central lung distance, field size, dose, and boost dose.

On cardiac MRI, they only saw two significant between-group differences. Time to peak filling rate was shorter for BCS patients (487 milliseconds vs. 647 ms for mastectomy patients; P = .02), but there was no difference in the peak filling rate itself. Left ventricular mass was smaller for BCS patients (mean 90.5 gm vs. 111 gm for mastectomy patients), but this difference was no longer significant after adjustment for systolic blood pressure, Dr. Simone noted.

"Interestingly, we didn’t see any evidence of myocardial fibrosis in any patient assessed, and only one patient in each arm had any degree of pericardial thickening," he said.

Reassuring Data

Additionally, investigators saw no significant differences on CT angiography in the presence of visible plaque or significant or severe vascular stenosis. There were also no differences in plaque or stenosis in the left anterior descending arteries of women treated with radiation for tumors on the left or the right side of the body.

"For each and every vessel we looked at, there was no difference in the degree of stenosis," Dr. Simone said.

Median CAC scores were low and in the normal range, but patients who had received chemotherapy had a trend toward increased atherosclerosis and plaque formation, Dr. Simone noted.

The study "gives some reassurance to our patients that, after 25 years of follow-up, using modern radiation techniques the delivery of radiation to the left does not cause cardiac toxicity," Dr. Bruce Haffty, chair of radiation oncology at the Cancer Institute of New Jersey, New Brunswick, said at a briefing.

The study was supported by the National Cancer Institute. Dr. Simone and Dr. Haffty reported no relevant disclosures.

Cardiac Toxicity Not Seen 25 Years after Breast Radiation