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9545 Background: We previously showed that standard-dose pembro plus reduced-dose ipi has manageable safety and robust antitumor activity in patients (pts) with advanced melanoma. Here, we present more mature data, including 1-y landmark PFS and OS estimates. Methods: In the phase 1 KEYNOTE-029 expansion cohort (NCT02089685), pts with advanced melanoma, ECOG PS 0-1, no active brain metastases, and no prior immune checkpoint inhibitor therapy received pembro 2 mg/kg Q3W + ipi 1 mg/kg Q3W for 4 doses, then pembro alone for up to 2 y. Primary end point was safety. Efficacy end points were ORR, PFS, and DOR per RECIST v1.1 by independent central review and OS. Results: 153 pts were enrolled between Jan 13, 2015, and Sep 17, 2015. Median age was 60 y, 66% were male, 25% had elevated LDH, 56% had stage M1c disease, 36% were BRAFV600mutant, and 13% received ≥1 prior therapy. As of Oct 17, 2016, median follow-up was 17 mo, and 64 (42%) pts remained on pembro. 110 (72%) pts received all 4 ipi doses. There were no treatment-related (TR) deaths. TRAEs occurred in all pts, were grade 3/4 in 69 (45%), and led to discontinuation of pembro and ipi in 17 (11%), ipi alone in 11 (7%), and pembro alone after ipi completion or discontinuation in 19 (12%). PD occurred in 1/11 pts who discontinued ipi alone and 4/17 pts who discontinued ipi and pembro. Of the 11 pts who discontinued ipi alone for a TRAE, 0 experienced recurrence of the same TRAE during pembro monotherapy and 2 discontinued pembro for a different TRAE (both elevated lipase). Immune-mediated AEs occurred in 90 (59%) pts and were grade 3/4 in 39 (25%). With 7 mo additional follow-up, there were 6 additional responses for an ORR of 61% (95% CI, 53%-69%); the CR rate increased from 10% to 15%. Median DOR was not reached (range, 1.6+ to 18.1+ mo), with 86/93 responders (92%), including 23/23 (100%) with CR, alive and without subsequent PD at cutoff. Median PFS and OS were not reached; 1-y estimates were 69% for PFS and 89% for OS. Conclusions: Pembro 2 mg/kg plus 4 doses of ipi 1 mg/kg has a manageable toxicity profile and provides robust, durable antitumor activity in pts with advanced melanoma. Clinical trial information: NCT02089685.

510 Background: The CTLA-4 antibody ipi and the PD-1 antibody pembro have demonstrated efficacy in pts with advanced malignancies. While these immune checkpoint inhibitors have shown robust activity as monotherapy, combination therapy may further improve outcomes. KEYNOTE-029 (NCT02089685) is a phase 1/2 study designed to assess the safety and efficacy of pembro + ipi or pegylated interferon alfa-2b (IFN-α) in pts with advanced melanoma or RCC. Here we report data from the phase 1 portion of the study in pts with RCC treated with pembro + ipi. Methods: Pts ≥18 years with advanced/unresectable or metastatic clear cell RCC who received ≥1 prior therapy for metastatic disease, had ≥1 measurable lesion per RECIST v1.1, and ECOG PS 0-1 were enrolled. Pts received pembro 2 mg/kg Q3W + low-dose ipi (1 mg/kg Q3W for 4 doses) until disease progression, unacceptable toxicity, investigator/patient decision, or 2 years of pembro treatment. AEs were monitored throughout treatment and for 30 days thereafter and graded per NCI CTCAE v4.0. Primary end point was safety; primary efficacy end point was ORR assessed per RECIST v1.1 by independent central imaging vendor review. Results: As of the March 17, 2016, data cutoff, 10 pts with RCC received pembro + low-dose ipi. 60% were male, 70% were white, median age was 61 years (range, 48-70 years), 40% received 2 prior lines of therapy, and 40% received prior immunotherapy. With a median follow-up of 17.4 months (0.9-23.5 months), 70% of pts experienced treatment-related AEs (TRAEs) of any grade, most commonly fatigue (30%); and 50% experienced grade 3/4 TRAEs, most commonly increased lipase (20%). 50% of pts discontinued pembro because of TRAEs, most commonly increased lipase (40%). There were no treatment-related deaths. ORR was 20% (2 partial responses); median duration of response was not reached (14.1+-17.1 months+). An additional 3 pts had stable disease; disease control rate was 50%. Conclusions: The combination of pembro + low-dose ipi for 4 doses, followed by pembro monotherapy, demonstrates a manageable toxicity profile and preliminary antitumor activity in pts with advanced RCC. Clinical trial information: NCT02089685.

6011Background: Current treatment options for patients (pts) with recurrent/metastatic (R/M) HNSCC who progress on platinum and cetuximab have very limited efficacy. Pembrolizumab, an anti–PD-1 ant...

3013Background: Pembro (anti–PD-1), ipi (anti–CTLA-4), and PEG-IFN (cytokine) are approved as monotherapy for treating melanoma. KEYNOTE-029 (NCT02089685) is a first-in-human, phase 1 study that in...

9506Background: Pembro (MK-3475), an anti–PD-1 antibody that prevents PD-1 from binding to its ligands, PD-L1 and PD-L2, is approved in several countries for treating advanced melanoma. In KEYNOTE-...