Abstract P4-14-12: Outcomes in hormone receptor positive, invasive lobular cancer in the era of endocrine monotherapy

Background:Invasive lobular carcinoma (ILC) accounts for up to 15% of all breast cancers and is clinically and biologically distinct from invasive ductal carcinoma (IDC). Despite that, women with early stage ILC are often treated similarly to IDC. However, several retrospective studies suggest that patients (pts) with ILC may not derive survival benefit from the addition of chemotherapy to endocrine therapy relative to pts with IDC. The purpose of our study was to compare outcomes of pts with ILC treated with chemotherapy with those who received endocrine monotherapy. Methods: A retrospective review of pts with ILC or pleomorphic lobular carcinoma treated at the Ohio State University James Cancer Center from 2004-2014 was performed. Clinico-pathologic characteristics, treatment summary and clinical outcomes were collected. Distant disease-free survival (DDFS) was defined as time from diagnosis to the first distant metastases or death and overall survival (OS) was the time from diagnosis to death or last known follow up. DDFS and OS curves were created using Kaplan-Meier methods and compared using log-rank tests. Cox proportional hazard models were used to calculate univariate and multi variable hazard ratios (HR) for OS and DDFS. Results: We identified 379 pts with early stage ILC (stage I: 43% (162/379), stage II: 34% (127/379), stage III: 22% (84/379), unknown: 1% (6/379)). The majority of pts were post-menopausal (79%), Caucasian (92%) and ER+/PR+ (87%) and HER2 negative (96%). One hundred seventy six pts (46%) received chemotherapy and 189 (50%) pts received endocrine therapy alone. Pts who received chemotherapy had stage II or III disease, positive lymph nodes and grade 2 or 3 tumors; while pts who received endocrine monotherapy had stage I disease, negative lymph nodes and grade 1 or 2 tumors. We found a 51% decrease in chemotherapy (from 63% to 31%) and an increase in endocrine monotherapy use (from 34% to 65%) between 2004-2010 and 2011-2014. One hundred thirty two pts were evaluated with Oncotype DX, of which 76% (100/132) were node negative with the majority having a low recurrence score (low: 64%; intermediate: 33%; high: 3%). The use of Oncotype DX increased from 21.1% in 2004-2010 to 47.9% in 2011-2014. We found that 112 of 149 pts with at least 5 years follow up (75.2%) successfully completed five or more years of endocrine therapy. Univariate cox models showed worse DDFS HRs for type of therapy and node status (HR: 2.36, p=0.005, HR: 4.16, p Conclusion: We found no difference in DDFS between endocrine monotherapy and chemotherapy after adjusting for age, grade, and nodal involvement in pts with early stage ILC. This supports the hypothesis that ILC may not derive a significant benefit from the addition of chemotherapy. We need more prospective clinical trials considering histology to better understand how best to treat ILC. Citation Format: Williams N, Liu J, Stephens J, Palettas M, Boutrid H, Sardesai S, Reinbolt R, Stover D, VanDeusen J, Noonan A, Wesolowski R, Lustberg M, Ramaswamy B. Outcomes in hormone receptor positive, invasive lobular cancer in the era of endocrine monotherapy [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-14-12.