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Abstract P3-09-04: Phase 2, open-label study of intratumoral tavokinogene telseplasmid (tavo) plus electroporation in combination with intravenous pembrolizumab therapy in patients with inoperable locally advanced or metastatic triple-negative breast cancer (mTNBC) (KEYNOTE- 890/OMS-I141)

2020; American Association for Cancer Research; Volume: 80; Issue: 4_Supplement Linguagem: Inglês

10.1158/1538-7445.sabcs19-p3-09-04

1538-7445

Melinda L. Telli, Irene Wapnir, Bianca Devitt, Katharine Cuff, Hatem Soliman, Shaveta Vinayak, David A. Canton, Christopher G. Twitty, Kellie Malloy Foerter, Rohit Joshi,

Toxin Mechanisms and Immunotoxins

Abstract BACKGROUND: Anti-PD-1 checkpoint inhibitor (CPI) monotherapy has demonstrated modest activity in pre-treated mTNBC, with single digit objective response rates (ORR) observed. Our prior data suggests that local electroporation after intratumoral administration of tavokinogene telseplasmid (IT-tavo-EP), a plasmid encoding the proinflammatory cytokine IL-12, can render CPI non-responsive pre-treated mTNBC sensitive to CPI therapy. The phase II KEYNOTE-890/OMS-I141 study was therefore designed to evaluate IT-tavo-EP and IV pembrolizumab in patients with mTNBC previously treated with chemotherapy +/- CPI therapy. METHODS: Patients with histologically confirmed inoperable locally advanced or metastatic TNBC with at least 1 line of prior systemic therapy for advanced disease, including prior CPI therapy, were eligible. Patients were required to have RECIST v1.1 measurable disease with at least 1 anatomically distinct cutaneous or subcutaneous lesion accessible for intratumoral injection and electroporation. Scans were obtained every 12 weeks. Patients received pembrolizumab 200 mg IV on day 1 of each 3-week cycle and IT-tavo-EP at a concentration of 0.5 mg/mL and dose volume of ~1/4 of the calculated lesion volume to the accessible lesion(s) on days 1, 5, and 8 every 6 weeks. The primary endpoint of this open-label, non-randomized phase II trial is ORR by investigator review. Secondary endpoints include safety and tolerability of the combined therapy, duration of response, progression-free survival (PFS), immune PFS and overall survival. The correlation between changes in the immune cell subsets and response to treatment was also evaluated. RESULTS: At the time of abstract submission, 16 of the planned 25 patients have been enrolled and 11 patients completed a post-treatment RECIST v1.1 assessment at the initial 12-week evaluation or discontinued prior to assessment. Patients had a median of 3 prior lines of therapy for advanced disease. Partial responses have been observed in 3 patients (ORR 27.3%), including a deep confirmed response in a patient with multiple liver, bone, skin and nodal metastases and a short disease-free interval following neoadjuvant chemotherapy. Regression of IT-tavo-EP untreated lesions have been observed. Treatment was well tolerated and any grade treatment emergent adverse events (AEs) regardless of attribution were observed in 11 of 16 (68.8%) [grade ≥3 in 6 of 16 (37.5%)]. Only one grade ≥3 AE was attributed to pembrolizumab and none were attributed to IT-tavo or EP. Patients demonstrated immunological responses in blood consistent with an IL-12-associated mechanism of action, including on-treatment reduction of peripheral gMDSC suppressors. Additional biomarker analysis of patient tumor and blood samples are ongoing. CONCLUSIONS: When compared to the results of KEYNOTE-086, which demonstrated a 5.3% ORR in pretreated mTNBC patients with pembrolizumab monotherapy, our preliminary data from patients who have reached an assessment time-point suggests that IT-tavo-EP may enhance sensitivity to pembrolizumab in this patient population. Updated data will be presented. Citation Format: Melinda L. Telli, Irene Wapnir, Bianca Devitt, Katharine Cuff, Hatem Soliman, Shaveta Vinayak, David A. Canton, Christopher Twitty, Kellie Malloy Foerter, Rohit Joshi. Phase 2, open-label study of intratumoral tavokinogene telseplasmid (tavo) plus electroporation in combination with intravenous pembrolizumab therapy in patients with inoperable locally advanced or metastatic triple-negative breast cancer (mTNBC) (KEYNOTE- 890/OMS-I141) [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 P3-09-04.