S2-1: Partial Breast Brachytherapy Is Associated with Inferior Effectiveness and Increased Toxicity Compared with Whole Breast Irradiation in Older Patients.
Authors: Smith GL , Xu Y , Buchholz TA , Giordano SH , Smith BD 
Published: June 2012

Background: Accelerated partial breast brachytherapy (APBI-brachy) is an increasingly popular radiation treatment for older patients diagnosed with early stage breast cancer. Despite growing utilization, there is a lack of population-based cohort studies as well as randomized phase III data to compare its effectiveness and toxicity profile with standard whole breast irradiation (WBI). The purpose of this study was to provide the first nationally comprehensive comparison of effectiveness and toxicity outcomes in older Medicare patients treated with APBI-brachy versus WBI.

Methods: Medicare billing claims identified beneficiaries age&gt;66 with incident invasive breast cancers diagnosed between 2000 and 2007 and treated with conservative surgery followed by APBI-brachy alone versus WBI. Cumulative incidence of subsequent mastectomy (a validated surrogate for local failure) was compared between the two treatment groups using the log-rank test. Adjusted risk of subsequent mastectomy was determined using a multivariate Cox proportional hazards model including demographic, socioeconomic, and clinical covariates. Risks of acute complications (hospitalization or infection within 120 days of radiation), were compared using the chi-square test. Adjusted odds of acute complications were determined using multivariate logistic models including covariates. Cumulative incidences of long-term toxicities (rib fracture, fat necrosis, breast pain, and pneumonitis) were compared using the log-rank test.

Results: In 130,535 women, use of APBI-brachy increased over time from &lt;1% of patients treated in 2000 to 13% of patients in 2007 (P&lt;0.001 for trend). Patients treated with APBI-brachy were less likely to have axillary lymph node involvement or to have received chemotherapy, and were more likely to be older, White, and have comorbid illness. At 5 years, the cumulative incidence of subsequent mastectomy was significantly higher in patients treated with APBI-brachy (4.0% in APBI-brachy vs. 2.2% in WBI, P&lt;0.001). On multivariate analysis, there was a two-fold increased risk for subsequent mastectomy in patients treated with APBI-brachy (HR= 2.14; 95% CI 1.83−2.52, P&lt;0.001). APBI-brachy was also associated with more acute complications, including a higher risk of hospitalization (9.6% vs. 5.7%; P&lt;0.001) (Adjusted OR= 1.71; 1.58−1.86); and infection (8.1% vs. 4.5%; P&lt;0.001) (Adjusted OR=1.85; 1.69−2.02; P&lt;0.001). APBI-brachy was also associated with higher 5-year cumulative incidence of rib fracture (4.2% vs. 3.6% in WBI), fat necrosis (9.1% vs. 3.7%), and breast pain (14.9% vs. 11.7%) (P&lt;0.001 for all comparisons), but a lower incidence of pneumonitis (0.1% vs. 0.8%, P&lt;0.001).

Discussion: APBI-brachy was associated with inferior effectiveness as well as increased acute and late toxicities compared with WBI in this cohort of older breast cancer patients. These data underscore the importance of awaiting mature results of randomized trials designed to prospectively compare these treatments before employing widespread adoption of APBI-brachy as an alternative to WBI in select patients.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S2-1.