A phase II study of pembrolizumab in combination with mFOLFOX6 for patients with advanced colorectal cancer.

Abstract

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Background: Pembrolizumab (PEM) has activity in patients with deficient mismatch repair (dMMR) colorectal cancer (CRC). Oxaliplatin (OX) and 5FU lead to immunogenic cell death and increased antigen presentation. We hypothesized that combining mFOLFOX6 and PEM may enhance immunogenic cell death and improve outcome in patients with CRC irrespective of MMR status. Methods: Subjects ≥18 years old with untreated, unresectable CRC were assigned to a single arm study. The study had a safety run in cohort of six patients (OX 85 mg/m ², leucovorin 400 mg/m ², 5FU 400 mg/m ², 5FU infusion 2400 mg/m ²over 46 hours) and PEM 200 mg Q 3 weeks, followed by a phase II cohort. The primary objective was median progression free survival (mPFS), with secondary objectives: safety and toxicity per CTCAE V4.03, median overall survival, response rate, immune related response, disease control rate, and molecular correlates. Results: Between 4/2015 and 9/2016, 30 subjects were enrolled with following characteristics: 11 female, 26 Caucasian, median age: 45 years (25-75), 3 with dMMR, 22 MMR-proficient, and 5 with no available data. During the safety run in, 2 patients had G3 febrile neutropenia (FN) and 1 G4 neutropenia. The data safety monitoring committee recommended dose reduction of mFOLFOX6 to OX 68 mg/m ², leucovorin 400 mg/m ², 5FU of 320 mg/m ², 5FU infusion of 1920 mg/m ²over 46 hours and PEM 200 mg Q 3 weeks. At the data cut off (12/29/16), median follow up was 24 weeks (10-66) and 27 patients remained on study. Rate of G3/4 toxicity associated with FOLFOX/PEM and PEM alone was 36.7% and 13.2%, respectively. No further FN was observed. No grade 5 toxicity was seen on study. Best response was recorded as: 1 complete response, 15 partial response (CR +PR = 53%), and 14 stable disease, with 100% DCR at 8 weeks. One patient with dMMR had resection after 2 months of therapy with complete pathologic response. MPFS has not been reached (95% CI: 5.5 months, NR). Conclusions: Based on these preliminary results, PEM/mFOLFOX6 has acceptable toxicity though demonstrated a suggestion of increased neutropenia in the initial cohort. Clinical activity was seen in patients with untreated advanced CRC including those with proficient MMR. Clinical trial information: NCT02375672.