Older women treated with breast brachytherapy may be less likely to preserve their breasts and face more complications than women undergoing whole-breast irradiation (WBI), according to a study published May 2 in the Journal of the American Medical Association.
In the last decade, breast brachytherapy has emerged as an alternative to WBI. However, brachytherapy lacks randomized data comparing it with standard radiation treatment following lumpectomy.
Brachytherapy treats a smaller volume of breast tissue than WBI, and may not allow complete tumor eradication, which may be associated with local recurrences and subsequent mastectomy, according to Grace L. Smith, MD, PhD, MPH, from the division of radiation oncology at MD Anderson Cancer Center in Houston, and colleagues.
Smith and colleagues sought to compare the likelihood of breast preservation, complications and survival for brachytherapy and WBI among a cohort of older women with breast cancer.
The researchers devised a population-based cohort study of 92,735 women aged 67 and older diagnosed with invasive breast cancer between 2003 and 2007 and followed up through 2008.
Brachytherapy use increased from 3.47 percent of patients diagnosed in 2003 to 12.53 percent of patients in 2007. The researchers reported a five-year cumulative incidence of subsequent mastectomy of 3.95 percent in women treated with brachytherapy vs. 2.18 in the WBI group.
Smith et al also observed a higher risk of infectious and noninfectious postoperative complications among patients treated with brachytherapy compared with WBI. These included breast pain at 14.55 percent and 11.92 percent, respectively; fat necrosis at 8.26 percent and 4.05 percent, respectively; and rib fracture at 4.53 percent and 3.62 percent, respectively. However, women treated with WBI had a higher five-year incidence of pneumonitis.
Meanwhile, at five years, survival was comparable in the two groups. Patients treated with brachytherapy had an overall survival rate of 87.66 percent and those treated with WBI had a rate of 87.04 percent.
“Exploratory subgroup analysis failed to identify any subset of patients demonstrating significant clinical benefit from brachytherapy compared with standard treatment,” wrote Smith et al.
The researchers noted that additional data are required to confirm the validity and generalizability of the findings. They referred to a prior registry trial (Cancer 2010;116(920):4677-4685) that demonstrated five-year recurrence risks in line with the mastectomy risks reported in the current study, but it lacked a control group. Other studies have reported conflicting results.
The ongoing study (RTOG 0413/NSABP B-39) is a randomized trial designed to address persistent questions about breast brachytherapy. However, data detailing local recurrence risks and long-term complications will not be available for some time.
Smith et al outlined a few facts for physicians and patients to consider in the risk-benefit assessment process. WBI is associated with five-year recurrence rates as low as 0.6 to 0.9 percent. On the other hand, the researchers wrote that breast brachytherapy outcomes might improve as physicians accumulate experience or as patient selection criteria are developed.
The researchers emphasized the need for further study in younger patients with other insurance status and for longer follow-up to determine the impact of time on relative risk of outcomes.
Limitations of the study included use of claims-based definitions of invasive cancer and radiation; inability to adjust for covariates, such as cancer stage, histopathology and surgical margins and the possibility of detection bias for complications related to a newer technique.
The study does not prove causality between brachytherapy treatment and subsequent mastectomy, local tumor recurrence or complications, but Smith et al wrote that prior studies have suggested a high prevalence of clinically occult spread of breast cancer to other parts of the breast.
“Although these [current] results await validation in the prospective setting, they also prompt caution over widespread application of breast brachytherapy outside the study setting,” concluded Smith and colleagues.
To read a commentary detailing about the flaws of the study design written by Robert Kuske, MD, co-principal investigator of the ongoing Phase III clinical trial NSABP B-39, click here.