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Y.C. Tan
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OA13 - Immunotherapy in Malignant Pleural Mesothelioma: Current Status of Trials and New Approaches (ID 392)
- Event: WCLC 2016
- Type: Oral Session
- Track: Mesothelioma/Thymic Malignancies/Esophageal Cancer/Other Thoracic Malignancies
- Presentations: 1
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OA13.02 - Phase II Trial of Pembrolizumab in Patients with Malignant Mesothelioma (MM): Interim Analysis (ID 6232)
14:20 - 15:50 | Author(s): Y.C. Tan
- Abstract
- Presentation
Background:
Pembrolizumab showed significant activity in PD-L1+ MM in a phase IB study (Alley, 2015). We are conducting a phase II trial (NCT02399371) of pembrolizumab in previously-treated MM patients to further characterize its activity in a larger, non-selected population, determine a PD-L1 expression threshold, and interrogate the microenvironment.
Methods:
Eligible patients have histologically-confirmed pleural or peritoneal MM, measurable disease, PS 0-1, disease progression on/after pemetrexed/platinum, 1-2 prior regimens, normal organ function, and available tissue. Patients receive 200 mg pembrolizumab IV Q21 days and CT scans Q9 weeks. Primary objectives: 1) determine the objective response rate in: A] an unselected population and, B] a PD-L1 positive population; 2) determine the optimal threshold for PD-L1 expression using the 22C3 antibody-based IHC assay (Qualtek). Exploratory correlatives profile the inflammatory microenvironment via: a) multi-color immunofluorescence of tumor infiltrating lymphocytes (TILs) and macrophages, b) RNA-based inflammation signatures/pathway activation, c) characterizing underlying mutations/copy number changes. Proceeding to a 2[nd] stage requires ≥3 responses in 35 patients. If an optimal threshold for PD-L1 expression is determined, the 2[nd] stage only enrolls above that threshold.
Results:
35 patients enrolled 5/15-2/16. 1 withdrew. Male 82%; median age 63 (range 26-85); PS 0/1 63%/37%; epithelial/sarcomatoid/biphasic/NOS: 69%/26%/3%/3%; pleural/peritoneal 86%/14%; 1 prior regimen: 60%. Mean cycles: 8.5 (range 1-18). Median progression-free survival: 6.2 months (95% CI: 3.2, 8.2). Median overall survival has not been reached. Partial response: 7 (21%), stable disease (SD): 19 (56%); progression: 6 (18%); early death: 2 (6%). Ten patients received treatment beyond progression; 20% subsequently achieved SD. Grade 3/4 toxicity: pneumonitis 6%, fatigue 6%, adrenal insufficiency 6%, colitis 3%, confusion 3%, hyponatremia 3%, neutropenia 3%. Grade 1/2 immune-related toxicities: hypothyroidism 17%, rash 14%, pruritus 11%, diarrhea 9%, uveitis 6%, arthralgia 6%, hepatitis 3%, infusion reaction 3%, mucositis 3%. Grade 5 toxicities: autoimmune hepatitis 3%, unknown 3%. PD-L1 expression by tumor proportion score (N=31): none (< 1%): 55%; low (1%-49%): 19%; high (≥ 50%): 26%. PD-L1 expression did not correlate with response (ROC area 0.62; 95% CI: 0.32, 0.94).
Conclusion:
Pembrolizumab has robust activity in PD-L1 unselected, previously-treated MM patients, with a response rate of 21% and a disease control rate of 76%. An optimal PD-L1 threshold could not be established in this small sample. The 2nd stage is enrolling an additional 30 patients without PD-L1 pre-selection. Correlative studies including CD8 TILs, macrophage characterization, and presence of T-regulatory cells will be presented. Funded by a grant from the Mesothelioma Applied Research Foundation.
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