Pembrolizumab With Liver-Directed or Peptide Receptor Radionuclide Therapy for Neuroendocrine Tumors and Liver Metastases

PRIMARY OBJECTIVES: I. To evaluate safety profile of pembrolizumab in combination with Peptide Receptor Radionuclide Therapy (PRRT), transarterial embolization, and radioembolization. II. To evaluate the best observed overall response rate (ORR) in lesion(s) not targeted for liver-directed therapy (abscopal effect) to pembrolizumab plus liver-directed therapy according to Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 for patients with metastatic well-differentiated (WD) neuroendocrine tumors (NET)s (WD-NETs). III. To evaluate the best observed ORR to pembrolizumab plus peptide receptor radionuclide therapy (PRRT) according to RECIST 1.1 for patients with metastatic grade 2 and 3 WD-NET (Ki-67 \> 10%). SECONDARY OBJECTIVES: I. To evaluate duration of response (DOR) in patients receiving pembrolizumab in combination with liver-directed therapies or PRRT. II. To evaluate progression free survival (PFS) in subjects treated with pembrolizumab in combination with liver-directed therapies or PRRT. III. Best observed radiographic ORR per modified RECIST (mRECIST) in lesions targeted for liver-directed therapy. IV. Duration of response in lesions targeted for liver-directed therapy by mRECIST. EXPLORATORY OBJECTIVES: I. To compare ORR, DOR, and PFS based on immune-related (ir)RECIST with the same measures assessed by RECIST 1.1. II. To correlate clinical outcomes (ORR, DOR, PFS) with baseline immune cell infiltration and programmed death-ligand 1 (PD-L1) staining in cycle 1 and cycle 5 tumor biopsies. III. To assess the level of PD-L1 expression in tumor tissue prior to liver-directed therapy (prior to PRRT) and 5 weeks following liver-directed therapy (following PRRT). IV. To assess T cell infiltration on the pre-177Lu-DOTATATE (pre-PRRT) and on the on-treatment tumor tissue biopsies. V. To assess baseline circulating T cell receptor (TCR) repertories and changes in TCR repertories with treatment, and correlate baseline and turnover of repertories to clinical outcomes. VI. To analyze the relationship between baseline tumor proliferative index (as measured by Ki67) and response to therapy. OUTLINE: Patients originally assigned to 1 of 3 groups. As of 09/15/2022, Groups 2 and 3 are closed to enrollment. GROUP I (PRRT): Patients receive pembrolizumab intravenously (IV) over 30 minutes on day 1. Treatment repeats every 21 days for up to 35 courses in the absence of disease progression or unacceptable toxicity. PRRT using 177Lu-DOTATATE(Lutathera®) will be offered to patients with somatostatin receptor positive (SSTR+) tumors with Ki-67 index \> 20% (well-differentiated grade 3). Patients may have any number of liver and/or extrahepatic lesions with liver parenchyma replacement by tumor \< 75%. 200±20 millicurie (mCi) of 177Lu-DOTATATE will be administered intravenously per treatment on outpatient basis. Patients will receive a total of four treatments of 177Lu-DOTATATE, administered every 8±1 weeks. Patients with partial response (PR) or stable disease (SD) by RECIST v. 1.1 after cycle 4 of pembrolizumab who were treated with PRRT (group 1) would continue to receive systemic IV administrations of 177Lu-DOTATATE every 8 +/-1 weeks for up to four (4) treatments. After completion of four (4) PRRT treatments, pembrolizumab may be administered alone for up to 35 cycles CLOSED - GROUP II (TRANSARTERIAL EMBOLIZATION (TAE)): Patients receive pembrolizumab as in Group I. Patients with any number of liver lesions, largest being no larger than 5 cm, who have \< 75% liver parenchyma replacement by tumors, undergo TAE over 2-3 hours, 3-7 days following the first dose of pembrolizumab. CLOSED - GROUP III (RADIOEMBOLIZATION (RE)): Patients receive pembrolizumab as in Group I. Patients with any number of liver lesions, largest measuring more than 5 cm, who have \< 75% liver parenchyma replacement by tumors, undergo yttrium-90 microsphere RE 3-15 days following the first dose of pembrolizumab. After completion of study treatment, patients are followed up at 30 days and then every 3-6 months thereafter.