Outcomes of pancreatic ductal adenocarcinoma (PDAC) patients treated with neoadjuvant stereotactic body radiation therapy (SBRT) or conventionally fractionated radiation therapy (CFRT).

Abstract

e16209 Background: Hypothesis: Neoadjuvant SBRT can improve survival when compared to CFRT in PDAC patients who received chemotherapy. Past retrospective studies have shown improved outcomes of definitive SBRT when compared to CFRT without accounting for chemotherapy.1 We aim to study the outcomes of neoadjuvant SBRT vs CFRT accounting for chemotherapy. Methods: The National Cancer Database (NCDB) was queried for cases of PDAC from 2004-2015. Patients who received surgery and chemotherapy were included. Exclusion criteria were prior hormonal therapy or immunotherapy, lack of pathological confirmation or lack of information about chemotherapy. Log-rank test and Cox proportional hazards model were used to compare survival by radiation modalities. Predictors for overall survival (OS) were identified. Propensity score-matched (PSM) analysis balancing for different variables including type of chemotherapy was conducted. Results: Among 1604 patients, 223 (13.9%) had SBRT, and 1381 (86.1%) had CFRT. The median survivals were 30.0 and 26.0 months ( P = 0.010), while the 2-year survival rates were 63.4% and 53.7% for SBRT and CFRT patients, respectively. SBRT tended to be offered to older patients (age≥65: 56.1% vs 47.3%, P = 0.018), healthier patients (CCI=0: 72.2% vs 63.6%, P = 0.016), patients with worse cT staging (cT3 and cT4: 80.7% vs 69.7%, P = 0.008) and patients who got more multi-agent chemotherapy (89.2% vs 50.5%, P < 0.001). In the cohort with positive clinical lymph nodes (cN+), CFRT tended to decrease the pN staging more when compared to SBRT ( P = 0.032) (Table). In multivariate analysis, multi-agent chemotherapy (HR, 0.72; P < 0.001) was associated with better OS. SBRT did not show significantly better OS when compared to CFRT (HR, 0.81; P = 0.13) after accounting for other covariates including chemotherapy. PSM (1:1 match) analysis matched 223 pairs. SBRT did not show significant OS benefit (HR, 0.80; P = 0.17) when compared to CFRT. Conclusions: SBRT may be superior to CFRT in univariate analysis. However, after accounting for multi-agent chemotherapy, there is no significant survival difference between neoadjuvant SBRT and CFRT. Studies with larger sample size are desired. Neoadjuvant CFRT offers more significant nodal down-staging in patients with clinically positive lymph nodes (cN+) when compared to SBRT. Reference: Zhong J, Patel K, Switchenko J, et al. Outcomes for patients with locally advanced pancreatic adenocarcinoma treated with stereotacticbody radiation therapy versus conventionally fractionated radiation. Cancer2017 Sep 15;123(18):3486-3493. pN staging of cN+ cohort[Table: see text]