S1066 High 1-Year Survival Rate of UnresecTable Pancreatic Cancer Size Smaller Than 4 cm in Diameter Treated With Concurrent EUS-RFA: An Average Treatment Effect on the Treated Weighted Survival Analysis

Abstract

Introduction: Treatment of small primary pancreatic ductal adenocarcinoma (PDAC), unresecTable due to of blood vessel involvement or distant metastasis, relies on systemic therapy only. We hypothesized that concurrent EUS-guided radiofrequency ablation (EUS-RFA) might control the primary tumor and improve patients’ outcomes. Methods: A prospective series of unresecTable PDAC patients with primary tumor size ≤4 cm who underwent EUS-RFA using a 19-gauge RFA needle (STARmed Koyang, Korea) from Jan 2017 – Jan 2022 were compared with matched historical controls. A propensity score was calculated using tumor size, staging, age adjusted Charleston Comorbidity Index (CCI), Chemotherapy regimen received, and interactions between CCI regimen and staging. This was used to reweight observations so covariate distribution in the chemotherapy only group equalled that of the RFA group (Average Treatment effect on the Treated weights). We used the VIVA combo RF system with an energy of 50 Watts and impedance of 100 Ohms. Chemotherapy was given if the patients were deemed tolerable by oncologists. The patients were followed for at least 12 months to see the survival rates. Results: 46 patients comprised of 11 patients in EUS-RFA group and 35 patients in control group were included in the analysis. The mean (SD) age was 63 (13.5) years in the RFA group and 68 (8.1) years in control group. Characteristics of patients, along with the standard mean differences before and after weighting are show in in Table. Median weighted survival was 14 months in the RFA group versus 6.1 months in the controls. The adjusted survival probability at 6 and 12 months was 73% and 64% in the EUS-RFA group, versus 69% and 17% in the controls. The hazard ratio (HR) for death was 0.38 (95%CI 0.17 to 0.84); p=0.016 in the RFA group versus the controls. Median weighted time to progression was 6.1 in the RFA group versus 3.9 months in the controls. The adjusted progression-free survival at 6 and 12 months in the EUS-RFA group were 55% and 36%, versus 28% and 4% in the controls; the HR for progression was 0.57 (95%CI 0.36 – 1.26); p = 0.16 in the RFA group versus controls. The adverse events were only mild abdominal pain which were observed in 8.3% of total RFA operations. Conclusion: In patients PDAC with primary lesions ≤4 cm that cannot be cured by surgery, EUS-RFA combined with chemotherapy resulted in improved survival and progression free survival with minimal adverse events.Figure 1.: Treatment outcomes compared RFA group with control group Table 1. - Baseline characteristics of the enrolled patients *Data are mean (SD) or n(%) as appropriate. Percentages are rounded to 1 decimal place and may not equal 100% Characteristic Raw (unweighted) After weighting Prospective cases (n=11) Historical controls (n=35) Prospective cases (n=11) Historical controls (n=35) Standardized mean difference p-value Mean age (years) 63 (13.5) 68 (8.1) Female sex, n(%) 9 (81.8) 22 (62.9) Mean CCI score 2.91 (2.4) 2.89 (1.3) 2.91 2.94 -0.055 0.98 Tumor diameter (cm) 3.25 (0.51) 3.10 (0.58) 3.25 3.25 0.008 0.90 Regimen, n(%) None 3 (27.3) 6 (17.1) 27.3 26.3 0.022 0.96 First-line 3 (27.3) 16 (45.7) 27.3 27.0 0.005 0.99 Second-line 5 (45.5) 13 (37.1) 45.5 46.7 -0.025 0.96 Staging Stage III 6 (54.6) 24 (68.6) 54.5 56.6 0.021 0.97 Stage IV 5 (45.5) 11 (31.4) 45.5 43.4 -0.021 0.97