Abstract PD04-02: Accelerated hypofractionated versus conventional whole breast radiotherapy for localised left-sided breast cancer: the effect on long-term cardiac morbidity

Abstract PURPOSE: Equivalent long-term outcomes have been demonstrated between conventional whole breast radiotherapy (CWBRT) and accelerated hypofractionated whole breast radiotherapy (AWBRT) for early-stage breast cancer. However, there is ongoing concern regarding the long-term risk of cardiac injury with AWBRT in women with left-sided breast cancer. The primary goal of this population-based study was to determine whether there was an increase in cardiac morbidity with AWBRT versus CWBRT based on hospital administrative data. MATERIALS AND METHODS: Between 1990 and 1998, 2706 women, aged less than 80 years with left-sided early-stage breast cancer were treated with post-operative radiotherapy (RT) to the breast or chest wall alone. Baseline patient, tumour and treatment factors were recorded in a provincial outcomes database, linked to hospital administrative databases and de-identified. Data from hospitalization records two years prior to RT were used to identify baseline cardiac risk factors (including hypertension (HTN), diabetes, hypercholesterolemia and prior cardiac events) and other comorbidities. There was a policy of using CWBRT for women with breast and chest wall radiotherapy planning separations of >23cm, so a propensity-score model was developed to balance cardiac and breast cancer risk factors between women who received AWBRT (42.5–44 Gy/16 fractions) versus CWBRT (45–50 Gy/25 fractions). The first event of a hospital admission for cardiac causes after RT was determined from hospitalization records. Cumulative incidence of cardiac morbidity was estimated at 10 years after RT for AWBRT versus CWBRT groups. Gray's test was used to test for differences in the cumulative incidence curves between the AWBRT and CWBRT groups. RESULTS: The median follow-up [range] was 13.2 [10–28] years. 485 women were treated with CWBRT and 2221 women were treated with AWBRT. The CWBRT group had a higher prevalence of diabetes, with a trend towards higher prevalence of HTN and other cardiac risk factors. Age, year of diagnosis, stage, grade, ER status, hormone and chemotherapy use were not statistically different between the RT groups. There was no statistically significant difference at 10 years in the incidence rate (as measured by first hospitalisation for cardiac morbidity) between the RT groups. The 10-year cumulative incidence of these hospitalization events for cardiac morbidity (95% CI) was 20.8% (19.1–22.5) with AWBRT and 22.1% (18.5–25.9) with CWBRT. This difference was not significant between raw unadjusted values (p = 0.07) or after propensity score adjustment with Gray's test (p = 0.2). Differences were also not statistically different at 15 years follow-up. These values are comparable with published long-term cardiac morbidity rates with CWBRT. Mortality due to cardiac cause was not statistically different between the two groups at 15 years follow-up. CONCLUSION: Hospitalization for a primary or contributing cardiac cause at 15 years follow-up was not significantly different between women with left-sided early-stage breast cancer treated with AWBRT versus CWBRT even after correcting for pretreatment cardiac risk factors and events. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD04-02.

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