Phase Ib (COSMIC-021) trial of cabozantinib (C) in urothelial carcinoma (UC) or C in combination with atezolizumab (A) in patients (pts) with UC, castrate resistant prostate cancer (CRPC) or renal cell carcinoma (RCC).

2019 ◽  
Vol 37 (7_suppl) ◽  
pp. TPS683-TPS683 ◽  
Author(s):  
Sumanta K. Pal ◽  
Ulka N. Vaishampayan ◽  
Daniel E. Castellano ◽  
Andrea Necchi ◽  
Carla M.L.- Van Herpen ◽  
...  

TPS683 Background: C is an inhibitor of tyrosine kinases involved in tumor growth, angiogenesis, and immune regulation, including MET, VEGFR, and TAM kinases (Tyro3, AXL, MER). Preclinical and clinical studies suggest that C promotes an immune-permissive tumor environment which may enhance response to immune checkpoint inhibitors (ICI) such as the anti-PD-L1 mAb, A. C is approved for pts with advanced RCC and has shown encouraging clinical activity in combination with a PD-1 targeting mAb in RCC, UC, and CRPC (Nadal et al 2017). A is approved for pts with advanced UC after prior platinum-containing chemo and for chemo-naïve pts with platinum ineligible UC or PD-L1+ cisplatin ineligible UC. Combination of C with A may enhance treatment efficacy in pts with genitourinary (GU) cancers. Here, we present the study design of an ongoing phase 1b trial of C + A which includes cohorts with advanced RCC, UC, and CRPC. Methods: This global multicenter, phase 1b, open-label trial will assess the safety, tolerability, activity, and pharmacokinetics of C or C + A (NCT03170960). The study comprises a dose-escalation stage and an expansion stage. The dose-escalation stage (3+3 design) is completed. C 40 mg qd + 1200 mg A q3w is the recommended dose for the expansion stage. In the expansion stage, 18 cohorts (each 30 pts) will be enrolled including 7 cohorts with GU cancers: (1) treatment naïve clear cell RCC; (2) non-clear cell RCC, treatment naïve or following systemic anticancer therapy; (3) UC after prior platinum-based therapy; (4) treatment naïve cisplatin-ineligible UC; (5) treatment naïve cisplatin-eligible UC; (6) UC after prior ICI therapy and (7) CRPC after prior enzalutamide and/or abiraterone. In addition, an exploratory cohort (30 pts) will evaluate single agent 60 mg C in pts with UC after prior ICI therapy. Pts will continue treatment as long as they experience clinical benefit per investigator or until unacceptable toxicity. The primary objective of the expansion stage is the objective response rate per RECIST 1.1 per investigator for each cohort. Secondary objectives will assess safety including immune related AEs. Clinical trial information: NCT03170960.

2019 ◽  
Vol 37 (4_suppl) ◽  
pp. TPS478-TPS478 ◽  
Author(s):  
Kristen Renee Spencer ◽  
Giridharan Ramsingh ◽  
Nehal Mohamed ◽  
Sumanta K. Pal ◽  
Lorenza Rimassa

TPS478 Background: C is an inhibitor of tyrosine kinases involved in tumor growth, angiogenesis, and immune regulation, including MET, VEGFR, and TAM family kinases (Tyro3, AXL, MER). Preclinical and clinical studies suggest that C promotes an immune-permissive tumor environment which may enhance response to checkpoint inhibitors such as the anti-PD-L1 mAb A. C significantly improved overall survival vs placebo in previously treated advanced HCC, and the combination of A and bevacizumab has shown synergistic activity in advanced HCC. Checkpoint inhibitors have shown clinical activity in advanced CRC primarily in pts with high microsatellite instability (MSI); combination with immune-modulating agents may enhance activity in pts with stable or low MSI. Likewise, combination therapy may improve response in pts with GC/GEJC resistant to standard chemotherapy. Here, we present the study design of an ongoing phase 1b trial which includes cohorts with advanced HCC, GC/GEJC, or CRC. Methods: This global, phase 1b, open-label trial will assess the safety, tolerability, preliminary efficacy, and pharmacokinetics of C in combination with A (NCT03170960). The study consists of a dose-escalation stage and an expansion stage. In the dose-escalation stage (3+3 design), a recommended C dose for combination with a standard dose of A will be established. In the expansion stage, 18 cohorts will be enrolled at the recommended dose of C + A including 3 cohorts with gastrointestinal cancers: (1) advanced HCC not previously treated with systemic therapy; (2) advanced GC/GEJC after progression on platinum- or fluoropyrimidine-containing therapy; and (3) advanced CRC after progression on fluoropyrimidine combined with oxaliplatin or irinotecan. Pts will continue treatment as long as they experience clinical benefit as judged by the investigator or until unacceptable toxicity. The primary objective of the expansion stage is the objective response rate for each cohort. Exploratory objectives include correlation of tumor and plasma biomarkers, immune cell profiles, and MSI status with clinical outcome. Clinical trial information: NCT03170960.


2018 ◽  
Vol 36 (6_suppl) ◽  
pp. TPS541-TPS541
Author(s):  
Neeraj Agarwal ◽  
Ulka N. Vaishampayan ◽  
Bradley Alexander McGregor ◽  
Marjorie C. Green ◽  
Nehal Mohamed ◽  
...  

TPS541 Background: Cabozantinib (CABO) is an oral receptor tyrosine kinase inhibitor of MET, VEGFR, and TAM family receptors (TYRO3, AXL, and MER). It is approved for patients (pts) with RCC after prior therapy with antiangiogenic therapy, and has demonstrated clinical activity in UC. In clinical studies, CABO exposure increased circulating CD8+ T cells and reduced immune-suppressive monocytes and Tregs. In preclinical tumor models, CABO increased MHC class 1 expression on tumor cells and reduced myeloid-derived suppressor cells. CABO may facilitate an immune-permissive tumor environment and may enhance response to immune checkpoint inhibitors. Atezolizumab (ATEZO), an anti-PD-L1 mAb, is approved for: locally advanced/metastatic UC in pts who are cisplatin-ineligible or have disease progression during/following platinum-containing chemo; pts with metastatic NSCLC and disease progression during/following platinum-containing chemo. We present the study design of an ongoing phase 1b study combining CABO with ATEZO in pts with locally advanced/metastatic UC or RCC. Methods: This multicenter, phase 1b, open-label study aims to assess safety, tolerability, preliminary efficacy, and pharmacokinetics of CABO in combination with ATEZO (NCT03170960). The study will enroll pts with advanced UC (bladder, renal pelvis, ureter, urethra) or RCC. It consists of two stages: dose escalation and expansion. In the dose-escalation stage (3+3 design), a recommended CABO dose for the combination will be established. In the expansion stage, four tumor-specific cohorts will be enrolled: 1) pts with UC who have progressed on/after platinum-containing chemo; 2) chemo-naïve pts with UC who are cisplatin ineligible; 3) chemo-naïve pts with UC who are cisplatin eligible; and 4) untreated pts with RCC with clear cell histology; the primary objective is to determine the objective response rate in each cohort. Exploratory objectives include correlation of tumor and plasma biomarkers, and changes in immune cell profiles with clinical outcome. The study has been initiated and enrollment target is 120 pts across the 4 expansion cohorts. Clinical trial information: NCT03170960.


2018 ◽  
Vol 36 (5_suppl) ◽  
pp. TPS42-TPS42 ◽  
Author(s):  
Manuel C. Maia ◽  
Neeraj Agarwal ◽  
Bradley Alexander McGregor ◽  
Ulka N. Vaishampayan ◽  
Toni K. Choueiri ◽  
...  

TPS42 Background: Cabozantinib (CABO) is an oral receptor tyrosine kinase inhibitor of MET, VEGFR, and TAM family receptors (TYRO3, AXL, and MER). It is approved for patients (pts) with RCC after prior therapy with antiangiogenic therapy, and has demonstrated clinical activity in UC. In clinical studies, CABO exposure increased circulating CD8+ T cells and reduced immune-suppressive monocytes and Tregs. In preclinical tumor models, CABO increased MHC class 1 expression on tumor cells and reduced myeloid-derived suppressor cells. CABO may facilitate an immune-permissive tumor environment and may enhance response to immune checkpoint inhibitors. Atezolizumab (ATEZO), an anti-PD-L1 mAb, is approved for: locally advanced/metastatic UC in pts who are cisplatin-ineligible or have disease progression during/following platinum-containing chemo; pts with metastatic NSCLC and disease progression during/following platinum-containing chemo. We present the study design of an ongoing phase 1b study combining CABO with ATEZO in pts with locally advanced/metastatic UC or RCC. Methods: This multicenter, phase 1b, open-label study aims to assess safety, tolerability, preliminary efficacy, and pharmacokinetics of CABO in combination with ATEZO (NCT03170960). The study will enroll pts with advanced UC (bladder, renal pelvis, ureter, urethra) or RCC. It consists of two stages: dose escalation and expansion. In the dose-escalation stage (3+3 design), a recommended CABO dose for the combination will be established. In the expansion stage, four tumor-specific cohorts will be enrolled: 1) pts with UC who have progressed on/after platinum-containing chemo; 2) chemo-naïve pts with UC who are cisplatin ineligible; 3) chemo-naïve pts with UC who are cisplatin eligible; and 4) untreated pts with RCC with clear cell histology; the primary objective is to determine the objective response rate in each cohort. Exploratory objectives include correlation of tumor and plasma biomarkers, and changes in immune cell profiles with clinical outcome. The study has been initiated and enrollment target is 120 pts across the 4 expansion cohorts. Clinical trial information: NCT03170960.


2021 ◽  
Vol 39 (15_suppl) ◽  
pp. 4580-4580
Author(s):  
Deepak Kilari ◽  
Aniko Szabo ◽  
Pooja Ghatalia ◽  
Tracy L Rose ◽  
Nicole Weise ◽  
...  

4580 Background: Despite advances in the treatment of clear cell RCC, there is a paucity of data to guide management of nccRCC due to the heterogeneity and rarity of these tumors. The clinical activity of new combination therapies (including immunotherapy (IO), anti-vascular endothelial growth factor inhibitors (VEGF), and mammalian target of rapamycin (mTOR) inhibitors) in metastatic nccRCC is not known. Methods: In this multicenter retrospective analysis, we explored the efficacy of combination systemic therapies in patients with nccRCC. Baseline and follow-up demographic, clinical, treatment, and radiographic data were collected. The primary endpoint was objective response rate (ORR) assessed by investigator review. Secondary endpoints include progression- free survival (PFS), disease control rate (DCR), median duration of response (DOR), overall survival (OS), and biomarker correlates. Results: Among 66 included patients, median age was 59 yr; 60% were male and 62% white. Histologies included papillary (38%), chromophobe (17%), unclassified (24%), translocation (12%), and other (9 %). Sarcomatoid and/or rhabdoid differentiation was present in 18%, 70% had prior nephrectomy, 86% were IMDC intermediate/poor risk, 29% and 32% had liver and bone metastasis respectively. 67% received combination treatment in the first line. Comparison of outcomes based on treatment regimen is shown in the table. Conclusions: Antitumor activity was observed with novel combinations in nccRCC which warrants further prospective studies. Response rates and survival with combination therapy in this dataset remain inferior to rates seen in clear cell RCC.[Table: see text]


Cancers ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2985
Author(s):  
Ian Chau ◽  
Nicolas Penel ◽  
Andres O. Soriano ◽  
Hendrik-Tobias Arkenau ◽  
Jennifer Cultrera ◽  
...  

Ramucirumab (anti-VEGFR2) plus pembrolizumab (anti-PD1) demonstrated promising antitumor activity and tolerability among patients with previously treated advanced cancers, supporting growing evidence that combination therapies modulating the tumor microenvironment may expand the spectrum of patients who respond to checkpoint inhibitors. Here we present the results of this combination in first-line patients with metastatic G/GEJ cancer. Twenty-eight patients (≥18 years) with no prior systemic chemotherapy in the advanced/metastatic setting received ramucirumab (8 mg/kg days 1 and 8) plus pembrolizumab (200 mg day 1) every 3 weeks as part of JVDF phase 1a/b study. The primary endpoint was safety. Secondary endpoints included progression-free survival (PFS), objective response rate (ORR), and overall survival (OS). Tumors were PD-L1-positive (combined positive score ≥ 1) in 19 and -negative in 6 patients. Eighteen patients experienced grade 3 treatment-related adverse events, most commonly hypertension (14%) and elevated alanine/aspartate aminotransferase (11% each), with no grade 4 or 5 reported. The ORR was 25% (PD-L1-positive, 32%; PD-L1-negative, 17%) with duration of response not reached. PFS was 5.6 months (PD-L1-positive, 8.6 months; PD-L1-negative, 4.3 months), and OS 14.6 months (PD-L1-positive, 17.3 months; PD-L1-negative, 11.3 months). Acknowledging study design limitations, ramucirumab plus pembrolizumab had encouraging durable clinical activity with no unexpected toxicities in treatment-naïve biomarker-unselected metastatic G/GEJ cancer, and improved outcomes in patients with PD-L1-positive tumors.


2017 ◽  
Vol 35 (15_suppl) ◽  
pp. e20646-e20646
Author(s):  
Prantesh Jain ◽  
Monica Khunger ◽  
Vinay Pasupuleti ◽  
Adrian V Hernandez ◽  
Vamsidhar Velcheti

e20646 Background: Drugs targeting the PD-1/PD-L1 pathway show significant clinical activity in non-small cell lung carcinoma (NSCLC). Nivolumab, pembrolizumab and atezolizumab are currently approved for NSCLC patients who have progressed while on platinum-based chemotherapy. Recently, pembrolizumab received FDA approval for treatment naive NSCLC patients with tumor PD-L1 expression of ≥50%. However, there is relative lack of data on comparative efficacy of these drugs in the chemotherapy naive versus post-chemotherapy setting. In the current meta-analysis we compare the efficacy and toxicity of these drugs in chemotherapy naïve patients with those who receive them as subsequent therapy (after previous chemotherapy). Methods: A systematic search of electronic databases (PubMed-Medline, EMBASE, Scopus) and major conference proceedings was done for all clinical trials using PD1/PD-L1 inhibitors. Objective response rates (ORR) for patients determined to have positive tumor PD-L1 expression (Tumor Proportion Score ≥1%) from all phase I-III trials investigating nivolumab, pembrolizumab, atezolimumab, durvalumab and avelumab for NSCLC were collected. Only single agent PD-1/PDL-1 inhibitor trials were included. The ORR across trials was combined using DerSimonian-Laird random effects models. Higgins’ I2 statistic was used to assess heterogeneity. Results: 19 trials (7 with treatment naïve patients [n = 651]; 14 with chemotherapy treated patients [n = 2205]; 2 with separate treatment naïve and previously treated arms) were included. Treatment naïve patients were found to have statistically significant higher efficacy [ORR 28.27%(95% CI 20.70-36.52)] than those who received these drugs as subsequent therapy [ORR 20.13% (95%CI 17.53-22.85) (p = 0.02). Treatment naive patients had statistically significant higher rates of all grade pneumonitis as comapred to previously treated patients (4.9, 95%CI 3.4-6.7 vs 3.0 95% CI 2.0-4.1). Conclusions: PD1/PDL1 therapy for advanced NSCLC has a significantly improved efficacy (based on ORR) when used in treatment naïve patients as compared to its use in patients who have been previously treated with chemotherapy.


2020 ◽  
Vol 38 (6_suppl) ◽  
pp. 440-440 ◽  
Author(s):  
Petros Grivas ◽  
Yohann Loriot ◽  
Susan Feyerabend ◽  
Rafael Morales-Barrera ◽  
Min Yuen Teo ◽  
...  

440 Background: ATLAS (NCT03397394) evaluated the efficacy/safety of the PARP inhibitor (PARPi) rucaparib in patients (pts) with previously treated locally advanced/unresectable UC or mUC. Methods: Pts with measurable disease who had progressed after 1–2 prior regimens (ie, platinum-based chemotherapy [PBC] and/or immune checkpoint inhibitors [ICI]) were enrolled regardless of tumor homologous recombination deficiency (HRD) status. Prior PARPi was not allowed. Pts received rucaparib 600 mg PO BID. Baseline tumor tissue or archival tissue ≤6 mo without intervening therapy was required; serial circulating tumor DNA samples were collected. Primary endpoint was investigator-assessed objective response rate (RECIST v1.1) in the intent-to-treat and HRD-positive (defined as genomic loss of heterozygosity ≥10%) populations. Key secondary endpoints: progression-free survival (PFS) and safety. Clinical benefit rate (CBR) was defined as complete or partial response or stable disease (SD) lasting ≥16 weeks. Results: As of Oct 7, 2019, 97 pts were enrolled (median age 66 y [range, 39–87]); most were men (n=76, 78.4%) and had ECOG PS 1 (n=65, 67.0%). Sixty-six pts (68.0%) had both prior PBC and ICI. Twenty pts (20.6%) were HRD-positive, 30 (30.9%) were HRD-negative and 47 (48.5%) had unknown HRD status; 4 pts had a deleterious BRCA1/2 alteration. Median time on treatment was 54 d (range, 2–224). There were no confirmed responses. Of 96 evaluable pts, 27 (28.1%) had a best response of SD; CBR was 12.5% and median PFS was 1.8 mo. No relationship was observed between HRD status and clinical activity. Treatment was discontinued by 93 pts (95.9%), mainly due to radiologic or clinical progression (73.1%). Most frequent any grade treatment-emergent (any cause) adverse events were asthenia/fatigue (n=56, 57.7%), nausea (n=40, 41.2%), and anemia (n=34, 35.1%). Conclusions: Single agent rucaparib did not show activity in pts with previously treated advanced UC and enrollment was suspended at the first interim analysis. The safety profile was consistent with that observed in pts with ovarian cancer. Next generation sequencing–based characterization of the genomic landscape of mUC will be presented. Clinical trial information: NCT03397394.


2012 ◽  
Vol 30 (15_suppl) ◽  
pp. 4545-4545 ◽  
Author(s):  
Igor Puzanov ◽  
Jeffrey Alan Sosman ◽  
Armando Santoro ◽  
Robert E. Martell ◽  
Grace K. Dy ◽  
...  

4545 Background: Inhibitors of vascular endothelial growth factor (VEGF) and VEGF receptor are standard therapy for RCC, and the MET signaling pathway is implicated in tumor angiogenesis. Tivantinib is an oral, selective MET inhibitor. In several tumor models, tivantinib plus sorafenib exhibited synergistic antitumor activity vs single-agent activity. This phase I dose-escalation study assessed the safety of tivantinib plus sorafenib in pts with advanced solid tumors. Methods: Endpoints were safety, the recommended phase II dose (RP2D) of tivantinib plus sorafenib, and antitumor activity. Previously, dose escalation established the RP2D as tivantinib 360 mg twice daily (BID) plus sorafenib 400 mg BID. Extension cohorts enrolled ≤ 20 pts each with RCC or other tumors. Patients were treated until disease progression or unacceptable toxicity. Results: 20 pts (mean age, 60 yr) including 16 clear cell, 3 papillary, and 1 clear cell/chromophobe RCC pts received treatment at the RP2D (n = 19) or tivantinib 360 mg BID plus sorafenib 200 mg BID (n = 1). 4 pts are still on study. 16 pts (13 with clear cell RCC) received ≥ 1 previous systemic therapy (median, 2; range, 0-4) including VEGF (14 pts) and/or mTOR (5 pts) inhibitors. The most common (≥ 25%) adverse events were rash (65%), diarrhea (45%), alopecia (40%), hypophosphatemia (35%), and fatigue, stomatitis, palmar-plantar erythrodysesthesia syndrome, and pruritus (25% each). Best response was partial response (PR) in 3 pts (all clear cell RCC pts) and stable disease (SD) in 15 pts (11 clear cell, 3 papillary, and 1 clear cell/chromophobe RCC pts). 7 pts with SD had ≥ 10% tumor size reduction. The overall response rate (ORR) and disease control rate (DCR; PR + SD) were 15% and 90%, respectively. Median progression-free survival (mPFS) was 12.7 mo (95% CI, 7.1-14.5 mo). In 14 pts previously treated with a VEGF inhibitor, best response was 2 PR and 10 SD, the ORR and DCR were 14% and 86%, respectively, and mPFS was 12.7 mo (95% CI, 5.3-NR mo). Conclusions: Oral combination therapy with tivantinib plus sorafenib was well tolerated and exhibited preliminary anticancer activity in pts with RCC, including pts pretreated with VEGF inhibitors.


2021 ◽  
Vol 39 (15_suppl) ◽  
pp. 3007-3007
Author(s):  
Sang Joon Shin ◽  
Jeeyun Lee ◽  
Tae Min Kim ◽  
Jin-Soo Kim ◽  
Yu Jung Kim ◽  
...  

3007 Background: Belvarafenib, a potent, selective RAF dimer (type II) inhibitor, exhibits clinical activity in BRAFV600E- and NRAS-mutant (NRASm) melanoma patients. The combination of belvarafenib and cobimetinib more potently and durably suppressed MAPK pathway output and tumor growth than currently approved BRAF/MEK inhibitors in RAS- or RAF-mutant tumor xenograft models. This interim results of phase 1b trial evaluated the safety, tolerability, pharmacokinetics, and anti-tumor activity of belvarafenib in combination with cobimetinib in dose-escalation and NRASm melanoma patients among the 9 indication-specific expansion cohorts. Methods: Patients with locally advanced or metastatic solid tumors harboring RAS or RAF mutation were enrolled in the dose-escalation stage, and the recommended doses were explored in the indication-specific expansion stage. Patients in the dose-escalation stage were given belvarafenib (100–300mg BID) in combination with cobimetinib (20–40mg QD) and the dose of subsequent cohorts was decided by a traditional 3+3 design and safety profile. Primary objectives were to evaluate the safety and tolerability, to estimate the maximum tolerable dose, and to identify the RP2D of the combination. Results: A total of 32 patients enrolled were evaluated for safety analysis; 19 were enrolled in 4 cohorts in the dose-escalation stage and 13 NRASm melanoma patients were enrolled in the indication-specific expansion stage (cut-off date: 2020-7-24). There were 3 DLTs (G3 colitis, G3 diarrhoea, G3 nausea) in 2 patients at the starting dose of belvarafenib 200mg BID continuously and cobimetinib 40mg QD 21/7 schedule. Belvarafenib dose was escalated to 300mg BID with cobimetinib 20mg QD, which did not result in DLTs. The most common treatment-emergent adverse events that occurred in ≥30% of 32 patients were dermatitis acneiform, diarrhoea, constipation, and increase in blood creatine phosphokinase. Two combination doses were explored in the indication-specific expansion stage. Out of the 9 indication-specific expansion cohorts, NRASm melanoma patients exhibited promising efficacy signal; 5 patients reached partial responses (PRs) out of 13, giving a response rate of 38.5%. Among them, 11 had been previously treated with checkpoint inhibitors (CPIs), including 5 (45.5%) who achieved PR. The median PFS was 7.3 months and 5 patients remained on the treatment at the cut-off date. Conclusions: Belvarafenib in combination with cobimetinib showed acceptable tolerability and encouraging efficacy in NRASm melanoma, and in those with prior CPI treatment. Further research is ongoing in other cohorts (Clinicaltrial.gov, NCT03284502) and in NRASm melanoma (reference GO42273 by clinicaltrials.gov ID number). *S.J.S and J.L contributed equally to this work. Clinical trial information: NCT03284502.


2021 ◽  
Vol 39 (15_suppl) ◽  
pp. 5053-5053
Author(s):  
Rahul Raj Aggarwal ◽  
Srey Luch Sam ◽  
Vadim S Koshkin ◽  
Eric Jay Small ◽  
Felix Y Feng ◽  
...  

5053 Background: Immune checkpoint inhibitors have limited single agent activity in microsatellite-stable mCRPC. 177Lu-PSMA-617 (Lu) is a PSMA-targeting radioligand therapy that has demonstrated promising anti-tumor activity. We sought to determine whether a single dose of Lu can induce an immunogenic priming effect to improve outcomes of men with mCRPC subsequently treated with pembrolizumab (P). Methods: We undertook a phase 1b, single arm trial enrolling chemotherapy-naïve mCRPC patients (pts) with progression (PD) on at least one prior androgen signaling inhibitor (NCT03805594). Pts were required to have ≥ 3 PSMA-avid lesions on 68Ga-PSMA-11 PET and measurable disease by RECIST 1.1 criteria. No genomic selection was undertaken. Pts were enrolled sequentially on one of three schedules: A) Single dose of Lu (7.4 GBq) followed by initiation of P (200 mg IV q 3 weeks) 28 days later; B) Lu x 1 dose given concomitantly with first P administration; C) Lu x 1 dose given on C2D1 following initiation of P on C1D1. Pts were treated with P until confirmed radiographic or clinical PD. The primary endpoint was safety; key secondary endpoints included PSA response, objective response rate by RECIST 1.1 criteria (ORR), median duration of response (DOR), and radiographic progression-free survival (rPFS). Results: 18 pts were enrolled, 6 per schedule. The median age was 64 (range 51 – 80) and 44% of pts had visceral metastases. The median baseline number of PSMA-avid metastatic lesions was 20 (range 6 – 50+). Six pts (33%) had progressed on prior abiraterone, 4 (22%) on enzalutamide, and 8 (44%) on both. There were no dose-limiting toxicities and one Grade ≥ 3 treatment-related adverse event (AE) (inflammatory arthritis, schedule B). There were no grade ≥ 3 hematologic AEs. The ORR was 8/18 (44%) and median DOR has not been reached (range 1.9+ – 15.9+ months). Four pts (2 on schedule A, 1 on schedule B, 1 on schedule C) with durable partial responses remain on study treatment for 5.4+, 8.9+, 9.2+, and 17.8+ months, respectively. The median rPFS was 6.5 months (95% CI: 2.5 – 9.8). PSA30, PSA50, and PSA90 response rates were 44%, 28%, and 17%, respectively. Fourteen pts (78%), including all durable responders, had somatic genomic data available. One (7%) harbored a DNA repair mutation ( BRCA1, non-responder), none were MSI-high, and all carried low tumor mutational burden (≤ 5 mutations/MB). Single cell sequencing of the immune microenvironment from paired metastatic tumor biopsies is underway. Conclusions: 177Lu-PSMA-617 as a priming dose followed by pembrolizumab was well tolerated and leads to durable responses in a subset of mCRPC without high mutational burden or microsatellite instability, suggesting a possible immunogenic priming effect of radioligand therapy. Further evaluation of the combination is ongoing in a phase 2 study. Clinical trial information: NCT03805594.


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