Ethnic and Racial (E/R) Differences in Early-Stage Breast Cancer Patients (Pts) Successfully Treated With Intra-Operative Radiation Therapy (IORT) Using Electronic Brachytherapy

Abstract

<h3>Purpose/Objective(s)</h3> E/R differences in early-stage breast cancer treatment outcomes are multifactorial. Women of Caucasian, Hispanic, Afro-American, Asian, Native American and other E/R who were ≥ 40 years with biopsy-proven breast cancer (invasive ductal carcinoma, ductal carcinoma in situ) ≤ 30 mm were consented in a prospective single-arm institutional review board-approved multi-institution clinical trial designed to determine the efficacy and outcome of single fraction IORT. E/R cohorts were analyzed for differences. <h3>Materials/Methods</h3> Between May 2012 and July 2018, 1200 enrolled pts were treated per protocol with lumpectomy plus a single 20 Gy fraction of IORT using disposable balloon electronic brachytherapy. Local standards of care guided adjuvant medical therapy. Follow-up was at 6, 12, and 18 months then yearly. Data collection included demographics, histopathology, prognostic factors, medical therapy, local recurrence (LR), and survival. Statistical analysis was performed using the Exact Chi-square, 2-sided test. <h3>Results</h3> 1200 pts (mean age: 66 years) had successful breast cancer treatment (mean size: 11.7 mm) using single fraction IORT per protocol. Median follow-up was 4 years. E/R was identified in 1162 pts. "Caucasian" was listed as the E/R in 950 (81.8%) pts (Body Mass Index (BMI): 29.2; Post-menopausal (PM): 92%, Grade (Gr) III/High: 15.9%, Triple Negative prognostic factors (TN): 1.6%). "Hispanic" was the E/R listing in 85 (7.3%) pts (BMI: 30.2, PM: 96%, Gr III/High: 20%, TN: 2.4%). "Afro-American" was the E/R listing in 81 (7.0%) pts (BMI: 32.8, PM: 92%, Gr III/High: 25.9%, TN:3.7%). "Asian" was the E/R listing in 40 (3.4%) pts (BMI: 26.2, PM: 90%, Gr III/High: 27.5%, TN: 0%). "Native American" was listed for 6 (0.5%) pts (BMI: 25.6, PM: 83%, Gr III/High: 16.7%, TN: 0%). Pt results by E/R, age, size, use of chemotherapy (Chemo), and LR are shown in Table 1. E/R cohort derived LR rates were not statistically different (<i>P</i> = 0.866). There was no breast cancer related death. <h3>Conclusion</h3> Utilization of single fraction IORT in this trial minimized known E/R disparities (access and delay in radiation therapy). Other E/R differences (BMI, menopausal status, tumor pathology and biologic factors, post-IORT breast cancer treatment) may have contributed to the reported E/R outcomes. Recurrence rates at median 4-year trial follow-up in Hispanics, Afro-Americans, and Asians were higher than that of Caucasian women, although the LR differences did not reach statistical significance.