Abstract P2-14-13: Comparison of survival outcomes between treatment with endocrine therapy and chemoendocrine therapy in patients with invasive lobular carcinoma

Background: Invasive lobular breast cancer (ILC) is the second most common histological type of invasive breast cancer and accounts for 10-15% of all breast cancer cases. It is commonly strongly hormone receptor positive and, in general, is considered to be less chemo-sensitive compared with invasive ductal carcinoma (IDC). The aim of this study was to compare survival outcomes among ILC patients treated with adjuvant endocrine therapy (ET) compared with chemoendocrine therapy (CET). We also sought to assess utilization of Oncotype Dx testing and distribution of Recurrence Score results among ILC patients treated at our institution. Methods: We conducted an IRB approved retrospective study at Cleveland Clinic Taussig Cancer Institute of patients with non-metastatic ILC. Patient diagnosed with ILC and treated from January 2004 through December 2017 were identified from our tumor registry. Patient characteristics including demographics, pathologic features, hormone replacement therapy (HRT) use, Oncotype Dx recurrence score, treatment details and recurrence data were obtained through medical chart review. Recurrence-free and overall survival (OS) were compared between ET and CET using Kaplan-Meier method and Cox proportional hazard model with consideration of differences on age and prognostic factors. The outcomes between age and pathological stage propensity score matched treatment groups were also compared. Results: A total of 638 patients (Mean age 61.9±11.7, 99.1% estrogen receptor positive, 82.6% progesterone receptor positive) were identified. 406 (63.6%) patients received ET and 232 (36.4%) patients received CET. Compared to ET, patients who received CET were significantly younger (Mean 56.3 vs 65.0 years) and more likely to be premenopausal (40.1% vs 14.6%), however they had significant worse prognostic features including pathological stage (stage III: 38.9% vs 2.1%), grade (≥ II: 69.0% vs 55.9%) and Oncotype Dx score (≥18: 72.4% vs 36.2%). Patients were followed for median (IQR) time of 4 (2.0, 6.4) years for survival outcomes. Although recurrence-free survival (local or distant) was worse in CET (5-year recurrence-free: 81.9% vs 96.5%), age and clinical prognostic features adjusted recurrence risk was similar as ET (Adjusted HR and 95% CI: 0.83, 0.36-1.92) and risk of death was also similar (Adjusted HR and 95% CI: 0.68, 0.31-1.50). Only 222 patients had Oncotype Dx score (35%), with 59% falling in the low risk range, 39% intermediate risk range and 2% high risk range. The Oncotype Dx recurrence score was not associated with recurrence or death. The recurrence-free (5-year: 97.4% vs 90.4%, p=0.37) and OS (At 5-year OS: 94.3% vs 89.4%, p=0.08) were also similar between age and pathological stage matched CET and ET groups. Conclusion: Use of chemoendocrine therapy did not result in improved survival outcomes for patients with ILC compared to those treated with endocrine monotherapy in the adjuvant setting. The majority of ILC patients did not have Oncotype Dx testing sent however when it was ordered, most cases resulted in the low-intermediate risk range, suggesting limited benefit of chemotherapy as reflected by survival outcome results observed. Citation Format: Mathew Thomas, Hong Li, Jame Abraham, Halle CF Moore, G Thomas Budd, Alberto J Montero, Megan L Kruse. Comparison of survival outcomes between treatment with endocrine therapy and chemoendocrine therapy in patients with invasive lobular carcinoma [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-14-13.