The Role of Tumor Bed Boost in Breast Cancer Patients with HER2-Positive Disease Treated with Breast Conservation Therapy

Abstract

Retrospective and post-hoc trial analyses have supported the omission of the tumor bed radiation boost in HER2-positive patients undergoing breast-conservation surgery in the era of HER2-directed therapy. In this analysis, we sought to describe the national patterns of care of tumor bed boost and its association with overall survival (OS) in this population. We queried the National Cancer Database to identify all female patients with HER2-positive invasive breast carcinoma treated with lumpectomy. Patients who were treated with neoadjuvant chemotherapy and those with metastatic disease at diagnosis were excluded from analysis. Clinical and demographic information and treatments were analyzed using standard T and χ2 tests. Predictors of receipt of tumor bed boost and predictors of death were identified with multivariable logistic regression. The Kaplan-Meier method was used to evaluated overall survival. We identified 6,620 female patients diagnosed with HER2-positive invasive breast carcinoma between 2006 and 2017. Of these patients, 2,825 (43%) were treated with a boost and 3,795 (57%) were not; 4,698 (71%) were hormone receptor positive and 1,909 (29%) were hormone receptor negative; 6,333 (96%) had negative surgical margins and 287 (4%) had positive surgical margins; 1,270 (19%) were ≤50 years of age and 5,350 (81%) were >50. On multivariable analysis, receipt of tumor bed boost was associated with age ≤50 years (Odds ratio [OR] 1.3, p<0.01), hormone receptor negative (OR 1.3, p<0.01). Factors associated with a higher risk for death included age >50 years (OR 2.4, p<0.01), positive surgical margins (OR 1.7, p<0.01), pN1 (OR 1.3, p = 0.03), pN2 (OR 2.3, p<0.01), pN3 (OR 3.2, p<0.02), and pT2 (OR 2.2, p<0.01) stage. Tumor bed boost was not associated with improved OS when compared to no boost among patients with HER2-positive disease who go on to receive adjuvant systemic therapy (HR 1.06, p = 0.60), even among patients who meet ASTRO tumor bed boost recommendation criteria (HR 0.90, p = 0.60), including age ≤50 with any grade, age 51-70 with high grade, or positive margin. A tumor bed boost is commonly implemented in HER2-positive breast cancer patients undergoing breast-conserving surgery and adjuvant radiation. This data supports previous retrospective and post-hoc trial analyses in omitting the tumor bed boost and treating patients who will receive adjuvant systemic therapy with whole breast radiation alone, provided that the patient receives HER2-directed therapy.