Abstract P1-15-10: Low utilization of hypofractionated radiotherapy for the treatment of early-stage breast cancer in the US
Authors: Mowery Yvonne M , Greenup Rachel A , Houck Kevin , Palta Manisha , Horton Janet K , Hwang Eun-Sil S , Sosa Julie A , Blitzblau Rachel C 
Published: May 2015

Background: Large randomized controlled trials have shown that hypofractionated whole breast irradiation (HF-WBI) is not inferior to or more toxic than conventionally fractionated whole breast irradiation (CF-WBI) for the treatment of early-stage breast cancer. Royal Marsden data were published in 2006 (10-yr), the Ontario trial was reported in 2002 (5-yr) and 2010 (10-yr), and the UK START trials were published in 2006 (5-yr) and 2013 (10-yr). We utilized the National Cancer Data Base (NCDB) to evaluate patterns of radiotherapy fractionation for early-stage, node-negative breast cancer in the U.S. We hypothesized that HF-WBI use would increase over time in response to emerging data supporting its use in this population.

Methods: We conducted a retrospective, population-based cohort study of women &gt;18 years diagnosed with T1-2N0 invasive breast carcinoma and treated with breast-conserving surgery between 2004 and 2011. Radiotherapy was categorized as accelerated partial breast irradiation (APBI; 38-40 Gy/1-10 fractions), HF-WBI (40-56 Gy/15-24 fractions) or CF-WBI (50-66 Gy/25-40 fractions). Patients treated with alternate fractionation were excluded. Patterns of breast radiotherapy fractionation were compared using the chi-square test. Multivariable logistic regression was performed for patients diagnosed in 2011, the year with the highest levels of HF-WBI utilization.

Results: 217,789 patients in the NCDB met inclusion criteria. HF-WBI use increased over time, rising from 2.1% among eligible patients in 2004 to 15.1% in 2011, while APBI use remained low at &lt;2%. Utilization of HF-WBI was significantly higher in academic centers than comprehensive community cancer centers and community-based cancer centers (p &lt;0.0001). This pattern persisted when controlling for T-stage, hormone receptor/HER2-status, diagnosis year, and patient age &gt;30 years. Table 1 shows frequency of HF-WBI use over time by center type. On multivariate analysis of patients diagnosed in 2011, the following factors were associated with higher use of HF-WBI: treatment at an academic center, older patient age, hormone receptor positivity, pT1 tumor size, and rural residence (Table 2).

Table 1: % HF-WBI use Community Cancer CenterComprehensive Community Cancer CenterAcademic Center20040.9%1.7%3.8%20051.6%2.1%3.8%20061.2%2.0%4.6%20071.5%2.8%7.1%20082.9%5.3%10.8%20093.9%8.5%14.7%20105.8%10.7%16.4%20119.6%13.9%20.5%

Table 2. Multivariate analysis, year 2011 (n=5568) OR95% CIAcademic Center vs. Community Cancer Center3.062.324.02Academic Center vs. Comprehensive Community Cancer Center1.781.532.08Patient age, 50-90 vs. 18-492.371.863.01T2 vs. T10.540.460.63HER2+ vs. Hormone Receptor +/HER2-0.750.590.97ER-/PR-/HER2- vs. Hormone Receptor +/HER2-0.660.520.84Rural vs. urban2.681.694.24

Conclusions: Utilization of HF-WBI in the US is rising, but remains low overall despite level I evidence showing its non-inferiority to CF-WBI. Given the advantages of HF-WBI in terms of patient convenience and potential healthcare system costs, further research is indicated to explore disparities in HF-WBI utilization in the US and to guide education of breast cancer providers.

Citation Format: Yvonne M Mowery, Rachel A Greenup, Kevin Houck, Manisha Palta, Janet K Horton, Eun-Sil S Hwang, Julie A Sosa, Rachel C Blitzblau. Low utilization of hypofractionated radiotherapy for the treatment of early-stage breast cancer in the US [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-15-10.