Phase Ib/II study of pembrolizumab with lanreotide depot for advanced, progressive gastroenteropancreatic neuroendocrine tumors (PLANET).

369 Background: Pembrolizumab has antitumor activity in a subset of GEP-NETs patients. We hypothesized that the lanreotide, by its antitumor effects and reduction of serotonin, a modulator of immunity, would synergize with pembrolizumab in low/intermediate grade GEPNETs. Methods: GEP-NETs patients who had progressed on a prior somatostatin analogue received lanreotide 90mg sq and pembrolizumab 200mg IV every 3 weeks until progressive disease or intolerable toxicity. The primary endpoint was ORR at any time on study and secondary endpoints were PFS and OS. Results: 22 patients were treated (F/M 10/12; Caucasian/AA/other 10/7/5; GI/pancreatic 14/8; median Ki67 5%, median time since diagnosis 5.3 yrs (IQR 2.3-7.9 yrs)). Prior octreotide LAR/lanreotide/both was administered to 20/1/1. Patients had a median of 2 prior systemic therapies (range 1-9) and six had prior locoregional therapy and 3 external beam radiotherapy. Of the 12 tumors analyzed thus far, 4 had detectable PD-L1 expression and 11 had detectable TILs. A median of 6 pembrolizumab doses (range 2-15) and 7 lanreotide doses (range 2-15) were administered. Six patients experienced treatment related SAEs (abdominal pain, pneumonitis, colitis, and hyperglycemia, all related to the pembrolizumab). Selected treatment related adverse events included: Hypothyroidism 23%, colitis 9%, hyperglycemia 14%, and pneumonitis 5%. Best response by RECIST 1.1 was SD/PD/Not available:39/52/9% and by irRECIST was 43/48/9%. Median PFS was 5.4 months (95% CI 1.7-8.3 mo). The median overall survival at a median follow-up of 15 months was not reached. Peripheral blood immunologic correlates will be reported subsequently. Conclusions: In a population of GEP-NET patients, progressing on a median of 2 prior therapies, including prior somatostatin analogue therapy, a minority of whom had PD-L1 expressing tumors, the combination of lanreotide and pembrolizumab produced stable disease in approximately 40% of patients. No new safety signals were identified. Clinical trial information: NCT03043664.

Duke Scholars

Author Hope Elizabeth Uronis Medicine, Medical Oncology