Pembrolizumab for advanced papillary or follicular thyroid cancer: preliminary results from the phase 1b KEYNOTE-028 study.

6091 Background: Treatment options are limited for patients (pts) with advanced thyroid cancer. PD-L1 expression in thyroid cancer tumors has been shown to correlate with poor prognosis. Pembrolizumab (pembro), an anti–PD-1 antibody, blocks the interaction between PD-1 and PD-L1 and PD-L2. We assessed the safety and efficacy of pembro in PD-L1+ advanced (unresectable and/or metastatic) thyroid cancer. Methods: KEYNOTE-028 (NCT02054806) is a nonrandomized trial of pembro in 20 types of advanced solid tumors. Key eligibility criteria for this cohort included papillary or follicular subtypes of advanced thyroid cancer, failure of standard therapy, ECOG PS 0-1, and PD-L1 expression in ≥ 1% of tumor or stroma cells by IHC. Pembro 10 mg/kg was given every 2 wk for up to 24 mo or until confirmed progression, intolerable toxicity, death, or withdrawal of consent. Response was assessed every 8 wk for the first 6 mo and every 12 wk thereafter. The primary end point was ORR per RECIST v1.1 by investigator review. Results: Of the 22 pts enrolled, median age was 60.5 y; 40.9% were male; 68.2% vs 31.8% had papillary vs follicular carcinoma; 36.4% had an ECOG PS of 1; 50.0% received ≥ 2 prior therapies for metastatic disease (18 pts were radioactive iodine refractory; 7 pts received prior sorafenib; 1 pt received prior lenvatinib). Median follow-up duration as of Dec 10, 2015, was 73.5 wk (range, 29.4-87.0). 18 (81.8%) pts had treatment-related adverse events (TRAEs); those occurring in ≥ 15% of pts were diarrhea (n = 7) and fatigue (n = 4). 1 TRAE of grade ≥ 3 (grade 3 colitis) occurred; no pts died or discontinued pembro because of a TRAE. 2 pts had a PR for an ORR (confirmed) of 9.1% (95% CI, 1.1-29.2); median duration of response was not yet reached (range, 35.3-44.1+ wk) by the data cutoff. The stable disease rate was 54.5% (n = 12, 95% CI, 32.2-75.6). The 6-mo OS rate was 100%; the 6-mo PFS rate was 58.7%. At the data cutoff, 6 pts remained on treatment. Conclusions: Pembro shows promising antitumor activity in advanced papillary or follicular thyroid cancer which progressed on standard therapies. The clinical benefit of pembrolizumab in advanced thyroid cancer will be further investigated in the phase 2 KEYNOTE-158 trial (NCT02628067). Clinical trial information: NCT02054806.