According to research presented at the American Society for Radiation Oncology's (ASTRO's) 55th Annual Meeting, early-stage breast cancer patients who undergo external beam therapy (XRT) are not at a greater risk for serious long-term side effects in the chest region, consisting of an increase in deaths via cardiac disease and secondary malignancies.
The study made significant use of patient information from the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) database. It examined women recognized as having primary Stage T1aN0 breast cancer (tumor of 5mm or less that has not yet spread to the lymph nodes), who underwent surgery, with or without post-operative radiation therapy, between 1990 and 1997.
The analysis was performed in order to determine if XRT was connected with a rise in mortality due to breast cancer, secondary cancer in the chest region, or cardiac conditions for these patients; only patients with breast cancer (BC) identified as the first malignancy were included. The women had an average age of 55-59 and were split into two groups: 2,397 who were administered XRT following surgery, and 2,988 who were not administered XRT following surgery.
Cause of death (COD) codes were employed to classify cardiac mortality, breast cancer mortality, and deaths from secondary chest cancers in order to evaluate overall survival (OS), breast cancer survival (BCS), second-tumor specific survival and cardiac-cause specific survival (CCS), and then draw a comparison between the XRT and non-XRT groups.
The occurrence of mortality was compared between the XRT and non-XRT groups using the Chi-Square test; and, the relative risk (RR) and allied 95 percent confidence interval (CI) were determined. Kaplan-Meier survival analysis and log-rank test were performed to evaluate OS, BCS, second-tumor specific survival and CCS.
At 10 years following treatment, OS rates were 91.6 percent for the XRT patients and 87 percent for the non-XRT group; BCS rates were 97 percent for the XRT patients and 95.7 percent for the non-XRT group; and CCS was 96.7 percent for the XRT patients and 92.7 percent for the non-XRT group.
Analysis of the results further illustrates that, with an average follow-up of 14 years there was no statistically significant difference in deaths from succeeding non-breast cancers in the chest area, the greater part of which were lung cancers. The number of deaths from cardiac causes was not that much higher for those patients treated with XRT for left-sided breast cancer, as opposed to those with right-sided breast cancer among the patient sample and time period reviewed. In fact, more women from the non-XRT group died from all causes, including cardiac causes, pointing out that those patients had worse general health conditions than the women who received radiation therapy.
"Breast conserving therapy, consisting of lumpectomy and XRT, has been an excellent approach to early breast cancer treatment, offering equivalent disease control and better cosmetic results compared to mastectomy as demonstrated by multiple randomized controlled trials in the past. Our study's results suggest that serious long-term side effects of radiation therapy, such as increase in deaths from cardiac disease and secondary malignancies, are rare. Radiation therapy is an integral part of early stage breast cancer treatment for those who choose to have a lumpectomy instead of a mastectomy, with its benefits likely far outweighing the potential risks in majority of the cases. The field of radiation oncology is rapidly changing, with new technology constantly being introduced that may reduce these risks further. Continued long term follow up and additional studies are needed to monitor for potential long term side effects,” said the study's presenting author and a second-year resident in radiation oncology at Weill Cornell Medical College in New York City, Jason Ye, MD.