Adherence to Endocrine Therapy Predicts Short-Term Clinical Outcomes for Postmenopausal Women With Luminal B but Not Luminal A Breast Cancer

Abstract

Although adjuvant endocrine therapy (ET) significantly improves outcomes for patients with hormone-receptor (HR)-positive breast cancer, studies suggest that adherence remains an issue, especially for older patients, who are largely underrepresented in clinical trials. This retrospective review will analyze the documented adherence to endocrine therapy and subsequent overall outcomes of breast cancer patients with Luminal A vs Luminal B genomic subtypes at our institution.224 women with newly diagnosed locoregional HR+ invasive breast cancer treated at our institution were retrospectively identified for analysis. Characteristics of the patient, tumor, and treatments were retrieved from the clinical chart. The Kruskal-Wallis and Pearson's chi-square tests were used to test differences between cohorts as appropriate. The Kaplan-Meier method was used to calculated adherence to ET, overall survival (OS), local-regional control (LRC), and distant metastasis (DM) from the date of diagnosis. Gene expression of tumor samples was assessed with a microarray analysis platform.Median follow up time was 71.4 months (range: 1.3-209.5). Median age at the time of diagnosis was 57 years (range: 25-91). There were 222 cases (91%) of ER+ disease, 181 cases (81%) of PR+ disease, and 34 cases (15%) of HER2-+ disease. Pathologic stage at diagnosis ranged from stage I (26%), stage II (48%), and stage III (26%). Local treatment included mastectomy alone (55%), mastectomy followed by radiation (34%), lumpectomy alone (3%), and lumpectomy followed by radiation (8%). There were 131 patients (56%) who received chemotherapy, and 189 patients (84%) who received ET. Patients ≥70 years of age were less likely to start ET (69% vs 91%, P = 0.0004). Of those who began ET (N = 189), patients ≥70 years old were less likely to remain adherent ET (2-year adherence 54% vs 75%, 5-year adherence 27% vs 50%, P = 0.048). Five-year OS, DM, and LRR were 87%, 10%, and 92%, respectively. Upon univariate log-rank analysis, adherence to ET for at least 2 years predicted improved OS (5-year OS 99% vs 64%, P < 0.0001), with a trend toward improved DM (5-year DM 6% vs 16%, P = 0.073). For luminal A patients (N = 112), adherence to ET ≥1 year was not associated with DM (P = 0.613) or LRC (P = 0.423). For luminal B patients (N = 75), adherence to ET ≥1 year was associated with improved DM (14% vs 44%, P = 0.02) and improved LRC (96% vs 76%, P = 0.02).Adherence to endocrine therapy significantly improved the LRC and DM for patients with luminal B but not luminal A breast cancer. Elderly patients with luminal B breast cancer should be cautioned against avoiding adjuvant treatments after surgery.