Key factors associated with response in the treatment of liver metastatic melanoma by cryoablation combined with PD-1 blockade therapy: The Cryo-Fire-001 study

e21500 Background: Liver metastasis remains a challenge in the treatment of advanced stage melanoma through immunotherapy. Although our previous study showed cryoablation could enhance the efficacy of PD-1 blockade therapy in the treatment of melanoma patients with liver metastasis, the key factors correlated with survival and treatment response remains unknown. Methods: Between 2018 and 2022, 45 melanoma patients receiving combined PD-1 blockade therapy and cryoablation of liver metastasis were retrospectively analyzed. The technical parameters of cryoablation, the sequence of the combined treatment, tumor characteristics, important immune markers and their correlations with treatment response were evaluated. The associations between key factors and overall survival (OS) were determined by Cox regression. Results: Of the 45 patients, the 3-month overall response rate (RECIST 1.1 criteria) is 26.7%. Multivariate analysis showed the number of metastatic organs ( > 2 vs ≤2; HR 3.54; 95% CI 1.32-9.49; P = 0.012), pretreatment LDH level ( > 300 vs ≤300 U/L; HR 4.59; 95% CI 1.78-11.85; P = 0.002) and diameter of ablated lesion ( > 30 vs ≤30 mm; HR 3.27; 95% CI 1.17-9.15; P= 0.024) were independent unfavorable prognostic factors for OS. Further analysis showed patients with larger intrahepatic tumors ablated had larger tumor size (P < 0.001). A scatter plot by the two key variables showed patients with intrahepatic tumor size less than 45 mm and size of ablated lesion less than 30 mm had a marginally higher rate of 3-month response (10/28, 35.7%) compared to those not (2/17, 11.7%; P = 0.076). Large diameter of ablated lesion ( > 30 mm) require more ablation needles and cause greater elevation in the level of IL-6, CD8+T cell to Treg cell ratio and neutrophil to lymphocyte ratio after cryoablation while these changes disappeared when tested one month later. Conclusions: Fine selection based on baseline characteristics of patients and size of intrahepatic lesion for cryoablation are essential to achieve a high response rate during cryoablation-PD-1 combination treatment for liver metastatic melanoma.