Breast Conservation among Older, Early Stage Breast Cancer Patients: Locoregional Recurrence Following Adjuvant Radiation or Hormone Therapy

Abstract

Following breast-conserving surgery (BCS), both radiation therapy (RT) and hormone therapy (HT) reduce the risk of locoregional recurrence (LRR) among favorable subgroups of breast cancer. Several studies have evaluated HT +/- RT, though local outcomes of HT versus RT monotherapy remain unclear. Indeed, many patients do not complete the full multi-year course of HT, yet little is known about LRR rates in absence of HT. Here, we evaluate rates of adjuvant HT and RT use in a cohort of favorable-risk patients over 65 years of age, and report LRR in the setting of adjuvant RT alone, HT alone, neither, or both. We analyzed a cohort of breast cancer patients ≥65 years of age with estrogen receptor positive (ER+), HER2/neu negative (HER2-) T1N0 breast cancer diagnosed between 2010 and 2015 and treated with BCS. Clinicopathologic features were collected including type of axillary surgery, RT modality, use of RT boost, duration of HT, chemotherapy, and OncotypeDx Recurrence Scores (RS). Cox regression analysis was conducted using time to LRR as the primary endpoint. A total of 1,016 women were included with a median age of 70 (IQR 67-75) and median follow-up of 4.9 years (range 0.4-7.7). Overall, 36 (4%) LRR events were observed and 16 (2%) patients had a distant recurrence. The 5-year overall survival rate for the cohort was 96%. A total of 624 (61%) patients received RT. While 894 (88%) were started on HT, 725 (72%) completed a full course or remain adherent at last follow-up. Evaluated by treatment group (with HT defined as fully compliant to date), 481 (48%) patients received both HT and RT (5-year LRR 2%, 95%CI 1-4%), 244 (24%) received HT alone (5-year LRR 4%, 95% CI 2-8%), 143 (14%) received RT alone (5-year LRR 5%, 95%CI 2-11%), and 142 (14%) received neither HT nor RT (LRR 11%, 95%CI 6-19%). LRR rates were significantly different between these four treatment groups (Log rank p<0.001). On Cox regression, accounting for clinicopathologic variables, lymphovascular invasion (HR 6.37, 95%CI 2.17-18.7; p<0.001) and adjuvant treatment group were significant predictors of LRR. Compared to neither HT nor RT, combination HT and RT was significantly associated with the greatest reduction in LRR (HR 0.11, 95%CI 0.04-0.29; p<0.001). HT or RT monotherapy each yielded similar reductions in LRR: HT alone (HR 0.28, 95%CI 0.11-0.71; p = 0.008) and RT alone (HR 0.29, 95%CI 0.10-0.84; p = 0.023). The risk of LRR following BCS is low among women ≥65 years of age with T1N0, ER+/HER2- breast cancer. RT and HT monotherapy each significantly reduce this risk to a similar extent. While the combination of RT and HT further reduces the risk of LRR in a statistically significant manner, the absolute benefit of this dual-approach is modest. Further study will elucidate whether appropriate patients may feasibly receive RT monotherapy rather than the current standards of HT monotherapy or dual RT and HT therapy.