The Value of Stereotactic Radiotherapy After FOLFIRINOX in Patients with Pancreatic Cancer with Vascular Contact: A Nationwide, Retrospective Cohort Study

Background/Objectives: Stereotactic body radiotherapy (SBRT) aims to prolong overall survival (OS) in patients with pancreatic ductal adenocarcinoma (PDAC) with vascular contact without progression of disease after (m)FOLFIRINOX. The primary objective of this study was to determine the potential value of SBRT. Methods: This nationwide, retrospective cohort study included patients with PDAC without progression of disease after at least four cycles of (m)FOLFIRINOX. The study comprised two cohorts, the SBRT and the No SBRT group. A landmark analysis excluded patients with a follow-up or OS time less than 12 months to minimize immortal time bias in the SBRT group. The primary outcome was OS from diagnosis. Secondary outcomes were the histopathological characteristics after resection. Results: Overall, 331 patients were included, of whom 231 were in the landmark analysis. In the overall cohort, the median OS was 20.7 months in the SBRT group versus 15.7 months in the No SBRT group (p = 0.004). In the landmark analysis, the median OS was 23.2 months in the SBRT group compared to 22.3 months in the No SBRT group (p = 0.554). These results indicate the presence of immortal time bias in the overall cohort in favor of the SBRT group. In the subgroup after resection, ypT0-2 (95% versus 76.5% [p = 0.026]), ypN0 (75% versus 37.3% [p < 0.004]), and absence of perineural invasion (50% versus 68.6% [p = 0.015]) were more prevalent in the SBRT group. Conclusions: In a landmark analysis, including only patients who survived at least 12 months after diagnosis, we found no difference in median OS between (m)FOLFIRINOX-only and (m)FOLFIRINOX with consecutive SBRT.