The SPIN Score, a Simple Clinical Score to Predict Pain Response Following Celiac Plexus Radiosurgery for Retroperitoneal Cancer Pain.

4211 Background: Celiac plexus radiosurgery is a novel non-invasive palliative treatment for pancreatic cancer pain that was recently added to NCCN guidelines. In the pivotal phase 2 trial (NCT03323489; Lancet Oncol 2024;25:1070-79), pain response was 53% (95% CI 42-64%). Prespecified exploratory analysis identified age and BMI as predictors; however, no clinically actionable patient selection tool was developed. We sought to identify additional predictors and create a practical risk stratification score. Methods: Post-hoc analysis of 90 evaluable patients from the phase 2 trial. Pain response was defined per protocol (≥2-point reduction in average pain from baseline to three weeks, on Brief Pain Inventory–Short Form). Candidate baseline predictors were examined by univariate and multivariate logistic regression. Only variables remaining significant in multivariate analysis were included in the final score to ensure independence and avoid overfitting. Internal validation used bootstrap resampling (500 iterations with replacement) to calculate optimism-corrected AUC. Analysis performed using Stata IC/16.1. Results: Univariate analysis identified 4 significant predictors: neurotoxic chemotherapy exposure (OR 5.33, 95% CI 2.13-13.4, p<0.001), baseline pain intensity (OR 1.73, p=0.003), age (OR 1.06, p=0.014), and therapy line (OR 0.65, p=0.04). On multivariate analysis, only neurotoxic exposure (OR 5.1, p=0.009) and baseline pain (OR 1.8, p=0.003) remained independently significant predictors. Age and therapy line lost significance due to collinearity. Dose-response analysis confirmed pain threshold optimization: >5 (61.5% response), >6 (65.8%), >7 (83.3%), >8 (85.7%), with >6 providing optimal discrimination. We created the SPIN (Severe Pain + Intact Nerves) score (0-2 points): baseline Pain >6 (+1), No prior Neurotoxic chemotherapy (+1). Response rates by score: 0 points: 32% (n=31); 1 point: 53% (n=40); 2 points: 89% (n=19). The 2-variable model achieved an apparent AUC=0.716. Following bootstrapping, the optimism-corrected AUC was=0.714. Conclusions: The simple score allows identification of distinct patient subgroups with markedly different probabilities of pain response following celiac plexus radiosurgery. This suggests the intervention should be considered earlier in the disease course, before exposure to neurotoxic agents. External validation is needed prior to clinical implementation. Financial support: Gateway for Cancer Research, The Israel Cancer Association. Clinical trial information: NCT03323489 .