Schwartzberg, Lee Steven

Abstract Endocrine based therapy is the standard treatment for estrogen receptor positive (ER+) MBC. Agents targeting the ER pathway including aromatase inhibitors (AIs), fulvestrant and tamoxifen along with CDK 4/6 inhibitors are considered standard for first and 2nd line treatment. However, endocrine resistance develops in nearly all patients and the optimal systemic therapy after progression on a CDK 4/6 inhibitor is unknown. Lasofoxifene is a third generation SERM previously investigated for the treatment of osteoporosis and vulvo-vaginal atrophy (VVA). In a large phase 3 trial evaluating the efficacy of lasofoxifene for the postmenopausal treatment of osteoporosis, lasofoxifene significantly reduced the incidence of ER+ breast cancer. Further unpublished preclinical data have demonstrated significant in vitro and in vivo efficacy in non-clinical breast cancer models including models with and without ESR1 mutants. Moreover, lasofoxifene significantly reduced metastases in ESR1 mutated models. These non-clinical and clinical data provide a strong rationale to pursue a phase 2 clinical trial in women with ER+, ESR1 mutated MBC. This open-label, multi-center study will compare the efficacy and tolerability of lasofoxifene (5 mg orally daily) to fulvestrant (IM 500 mg D1,15,29 and then q30 D) in a 1:1 randomization. Inclusion criteria include postmenopausal women with ER+ advanced breast cancer; progression on a non-steroidal AI in combination with a CDK 4/6 inhibitor; and a known ESR1 mutation. Approximately 90 patients with measurable or evaluable disease (i.e. bone only) will be recruited to have at least 40 patients per treatment arm. The primary endpoint will be progression free survival (PFS) with secondary endpoints of objective response rate (ORR), clinical benefit rate (CBR), duration of response (DoR) and time to response (TTR). It is assumed that lasofoxifene will double the median PFS compared to fulvestrant in this ESR1 mutation patient population for a hazard ratio 0.5 and a power of 89% to reach a 1-sided p of <0.05. The study will commence in 4Q2018 and will complete recruitment in 1 year. It is anticipated that 25-30 centers in the US will be participating. Citation Format: Plourde PV, Schwartzberg LS, Greene GL, Portman DJ, Komm BS, Jenkins SN, Liu P-Y, Portman MD, Goetz MP. An open-label, randomized, multi-center phase 2 study evaluating the activity of lasofoxifene relative to fulvestrant for the treatment of postmenopausal women with locally advanced or metastatic ER+/HER2 - breast cancer (MBC) with an ESR1 mutation [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 OT1-01-02.

Abstract Background: PARP inhibitor (PARPi) monotherapy has previously demonstrated clinical activity only in patients with a germline BRCA mutation (BRCAmut), while single-agent anti-programmed cell death protein 1 (PD-1) therapy has achieved response rates of only 5–20% in advanced triple negative breast cancer (TNBC). In preclinical studies, PARP inhibition enhanced anti-tumor immunity, increased infiltration of proliferating CD8+ T cells, and synergized with anti-PD-1 agents in BRCA wildtype (wt) tumors. TOPACIO is a fully enrolled, phase I/II trial of niraparib + pembrolizumab (pembro) in advanced TNBC. This combination achieved 28% objective response rate (ORR) and 50% disease control rate (DCR) in evaluable patients. Although activity was highest in patients with BRCAmut (ORR=60%; DCR=80%), durable clinical benefit was also observed in patients without BRCA mutations. In this study, we conducted exploratory biomarker analyses to evaluate their potential correlation with durable clinical benefit (any complete response [CR] or partial response [PR] regardless of duration or stable disease [SD] for ≥16 weeks) beyond BRCA mutations. Method: ORR was assessed by RECIST v1.1. Duration of disease control (DDC) was defined as time from first dose of study treatment to radiologic disease progression or death. Tumor mutational status of homologous recombination repair (HRR) and other DNA damage repair (DDR) pathway genes was determined using an NGS panel. Immunoprofiling was conducted using NanoString IO360 panel complimented with 30 DNA repair spike-ins. Tumor immune micro-environment was characterized using multiplex immuno-fluorescence (CycIF). PD-L1 status was determined using the Agilent/DAKO 22C3 IHC clinical trial assay. Results: Of 46 evaluable patients, 20 achieved durable clinical benefit (any CR/PR or SD≥16 weeks) with niraparib + pembro combination, of which 8 were tumor BRCA wild type (wt), and 1 was BRCA unknown. Of the 9 BRCAwt/unknown patients, 5 had deleterious mutations in HRR/DDR pathway genes, whereas the remaining 4 had no mutations (HRR/DDR wt). Mutations that were associated with response include CHEK1 (CR; DDC=10.3 mos), ATR (CR; DDC=6.4 mos), PALB2 (PR; DDC=3.5 mos), BLM (SD; DDC=8.1 mos), and NBN/RAD51C (SD; DDC=3.7 mos). Of 4 patients that had no identified mutations (HRR/DDR wt), 1 patient had CR; DDC=10.3 mos, and the remaining 3 patients had SD with DDC ranging from ∼4-8 mos. Of note, all 4 HRR/DDR wt patients were also PD-L1-negative. Table:Durable clinical benefit in BRCAwt/unknown patientsHRR/DRR MutationsPD-L1 StatusBest ResponseDDC (Months)CHEK1+CR10.3†ATR+CR6.4PALB2*UnknownPR3.5BLM-SD8.1NBN/RAD51C+SD3.7None-CR10.3†None-SD8.2None-SD4.2None-SD3.9*BRCA status unknown; †Treatment is ongoing. Conclusion: Patients with mutations beyond BRCA achieved durable clinical benefit with niraparib + pembro treatment; five of these patients had DDC >6 mos. Mutations in genes that are associated with the HRR/DDR pathway appear to confer sensitivity to niraparib + anti-PD1. Additional translational analyses, including immunoprofiling and CycIF, will be presented. Funding: TESARO, Inc., Waltham, MA, USA sponsored the study. Citation Format: Vinayak S, Tolaney SM, Schwartzberg L, Mita M, McCann G, Tan AR, Wahner Hendrickson A, Forero A, Anders C, Wulf G, Dillon P, Lynce F, Zarwan C, Erban J, Färkkilä A, Zhou Y, Buerstatte N, Graham JR, Arora S, Dezube B, Telli ML. Durability of clinical benefit with niraparib + pembrolizumab in patients with advanced triple-negative breast cancer beyond BRCA: (TOPACIO/Keynote-162) [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 PD5-02.