Background: Percutaneous image-guided cryoablation (cryo) is an established minimally invasive oncologic treatment that modulates the immune microenvironment. We hypothesized that cryo can augment anti-tumor responses in melanoma patients progressing on immune checkpoint inhibitors (ICI). Methods: In this non-randomized phase II single-center study, subjects with unresectable melanoma progressing on ICI underwent cryo of an enlarging lesion and ICI continuation for a minimum of 2 additional cycles. Computed tomography was performed at 6-8 weeks following cryo to determine tumor response in non-ablated lesions per RECIST1.1, with confirmatory scans at 8-12 weeks. The primary endpoint was safety and feasibility. Secondary endpoints were overall response rate (ORR) and disease control rate (DCR) with DCR defined as the percentage of pts who achieve complete response (CR), partial response (PR), and stable disease (SD). Correlative analyses on pre- and post-cryo tumor biopsy and blood samples were performed. Results: From May 2018 through July 2020, 20 pts were screened, 18 enrolled and 17 treated per protocol. All pts received prior PD-1/PD-L1 monotherapy and 12 (67%) experienced primary resistance to ICI. Median follow-up was 8.5 months. Ablated lesions included lymph nodes (n = 4), lung/pleura (n = 4), soft tissue/bone (n = 3), adrenal (n = 3), chest wall (n = 1), and kidney (n = 1). Peri-procedural events occurred in 3 cases (pneumothorax, diaphragm puncture, osteomyelitis). One pt. with underlying ICI-induced hypophysitis experienced an adrenal crisis post-procedure, which rapidly corrected with stress-dose steroid administration; there were no de novo immune-related adverse events post-ablation and there were no grade 4/5 events. In evaluable pts (n = 17), ORR was 18% and DCR was 47% (3 PR, 5 SD). To investigate the inflammatory state of the tumor microenvironment prior to cryo, PD-1, CD8+ TIL IHC, was performed and will be presented at the meeting. Additional exploratory analyses (serial ctDNA analysis, single cell RNA sequencing, HLA-subtyping) are ongoing. Conclusions: Cryoablation in patients with unresectable melanoma following progression on ICI is feasible with an acceptable side effect profile. Efficacy data of this potentially synergistic approach in metastatic melanoma is encouraging. Correlative analyses are underway to identify biomarkers of response to this novel strategy. Clinical trial information: NCT03290677

*Out of 17pts; 1pt did not have subsequent ICI and lacks confirmatory imaging.