Abstract P4-14-07: Neoadjuvant exemestane or exemestane plus docetaxel and cyclophosphamide tailored by clinicopathological response to 8–12 weeks' exemestane exposure for ER+/HER2– postmenopausal breast cancer patients

Abstract

Abstract Aim To investigate the efficacy and safety of initial neoadjuvant endocrine therapy with exemestane (EXE) alone followed by tailored treatment: continued EXE monotherapy for responders or EXE plus docetaxel–cyclophosphamide (TC) combination therapy for non-responders. Methods This open-label phase II study enrolled postmenopausal patients with primary invasive estrogen receptor (ER)-positive, HER2-negative, stage I–IIIA (T1c–T3 N0–2 M0) breast cancer and Ki67 index ≤30%. Patients first received EXE 25 mg/day for 12 weeks. Based on clinical response and change in Ki67 index, responders were defined as patients who achieved complete response (CR), partial response (PR) with Ki67 index ≤5% after treatment, or stable disease (SD) with Ki67 index ≤5% both before and after treatment. Non-responders were defined as patients with PR and Ki67 index >5% after treatment, or SD and Ki67 index >5% before or after treatment. For the subsequent 12 weeks, responders continued EXE monotherapy (continued EXE group) and non-responders received EXE plus 4 cycles of TC (docetaxel 75 mg/m2 and cyclophosphamide 600 mg/m2 every 3 weeks) (EXE+TC group). Primary endpoint was clinical response (CR and PR) at week 24. Results A total of 58 patients (median age 60 years, range 53–67 years) were enrolled between December 2010 and May 2016. Five patients discontinued treatment in the initial 12-week EXE monotherapy period; therefore 53 received the subsequent treatment. After 8–12 weeks of initial EXE monotherapy, 15 patients were classified as responders (8 with PR and Ki67 index ≤5% after treatment, 7 with SD and Ki67 index ≤5% before and after treatment) and 38 as non-responders (5 with PR and Ki67 index >5% after treatment, 33 with SD and Ki67 index >5% before or after treatment). Clinical response rates at weeks 12 and 24 were 71% (10/14, 95%CI 41.9–91.6%) and 57% (8/14, 95%CI 28.9–82.3%), respectively, in the continued EXE group, and 16% (4/25, 95%CI 4.5–36.1%) and 56% (14/25, 95%CI 34.9–75.6%), respectively, in the EXE+TC group. At week 24, no significant difference was found in median Ki67 index between the continued EXE and EXE+TC groups (1.4% and 2.0%, respectively). The proportion of patients with preoperative endocrine prognostic index (PEPI) 0 was higher in the continued EXE than in the EXE+TC group (60% vs 29%), but not significantly so (P=0.058, Fisher's exact test). The breast-conserving surgery rate was 93% and 56% (continued EXE and EXE+TC groups, respectively). Adverse events (AEs) ≥grade 3 were reported in 40% (21/53) of patients (continued EXE group 8%, 1/15; EXE+TC group 53%, 20/38). The most common AEs were leukopenia (37%, 14/38), neutropenia (32%, 12/38), and febrile neutropenia (16%, 6/38) during chemotherapy (EXE+TC group). Conclusion Tailored treatment maintained the favorable clinical response to EXE alone in responders and improved subsequent clinical response in non-responders. EXE+TC was associated with higher incidence of hematological AEs, but these were manageable. The results show the effectiveness of tailored neoadjuvant endocrine and chemoendocrine therapy in postmenopausal ER-positive breast cancer patients. (JBCRG-11TC; UMIN000004752) Citation Format: Yasojima H, Sato N, Masuda N, Morimoto T, Ueno T, Kanbayashi C, Kaneko K, Saji S, Sasano H, Morita S, Ohno S, Toi M. Neoadjuvant exemestane or exemestane plus docetaxel and cyclophosphamide tailored by clinicopathological response to 8–12 weeks' exemestane exposure for ER+/HER2– postmenopausal breast cancer patients [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 P4-14-07.