Abstract P3-13-06: Efficacy of eribulin in patients with invasive lobular carcinoma of the breast: data from a pooled analysis

Background: Invasive lobular carcinoma (ILC) represents the second most common breast cancer (BC) subtype and is usually characterized as hormone-receptor positive, low-to-intermediate histologic grade, and human epidermal growth factor receptor (HER) 2-negative. In the early-stage setting, ILCs are associated with lower rates of pathological response to preoperative chemotherapy compared with invasive ductal carcinoma (IDC). This exploratory analysis investigated the magnitude of benefit of single-agent eribulin for the treatment of advanced ILC using data from three clinical trials in women with advanced BC. We also describe the patterns of response and survival outcomes compared with IDC. Methods: Individual patient (pt) data from the experimental arms of two phase III studies (305 and 301) and a single-arm, phase II study were pooled for the present analysis. Study 305 (EMBRACE) randomized pts treated with ≥2 lines of chemotherapy for advanced BC to receive eribulin or treatment of physician9s choice. In study 301, pts treated with ≤2 lines of chemotherapy for advanced BC were randomized to receive eribulin or capecitabine. In the phase II study, pts who had received ≥3 lines of chemotherapy were treated with eribulin. Overall survival (OS) and progression-free survival (PFS) analyses were adjusted by study, estrogen receptor (ER) and HER2 status, and number of lines of therapy for advanced disease. Results: The three studies included 1353 eribulin-treated pts. Of the 1152 pts included in the present analysis, 118 were classified as ILC and 1034 as IDC. Median age of ILC and IDC pts was 58 years and 55 years, respectively. ER and/or progesterone receptor (PgR) positivity was more common in ILC (ER = 69%, PgR = 55%) than IDC (ER = 60%, PgR = 48%), while HER2 positivity was less frequent in ILC than IDC (9% vs 16%). A total of 52.5% of ILC and 61.4% of IDC pts received ≥3 lines of chemotherapy (for any stage BC) prior to eribulin. Pts with ILC and IDC had similar median OS (13.4 vs 13.5 months; hazard ratio [HR] = 1.10; 95% confidence intervals [CIs] 0.87, 1.38) and PFS (4.1 vs 3.6 months; HR = 0.91; 95% CIs 0.72, 1.14). Investigator-evaluated tumor response rates are shown in the table. Conclusions: In this exploratory, pooled analysis, magnitude of benefit from single-agent eribulin did not differ between the ILC and IDC cohorts. While there was a limited numbers of pts with ILC, response rates, PFS, and OS were similar for the two pt groups. The results with eribulin for advanced ILC contrast with data for other agents in early-stage settings, where ILC is generally less responsive to chemotherapy than IDC. These findings may, however, underline changes in the disease biology after exposure to previous therapies or changes inherent to disease progression. Citation Format: Javier Cortes, Jose Perez, Yi He, Otto Metzger-Filho. Efficacy of eribulin in patients with invasive lobular carcinoma of the breast: data from a pooled analysis [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-13-06.