Clinical outcomes of adjuvant chemoradiotherapy in pancreatic adenocarcinoma with R1 resection.

731 Background: The benefit of chemoradiotherapy (CRT) following adjuvant chemotherapy in pancreatic cancer is unclear, though recent findings suggest some disease-free survival benefit over chemotherapy alone. We aimed to assess overall (OS) and progression-free survival (PFS) and patterns of disease recurrence following adjuvant chemoradiotherapy (CRT) in pancreatic adenocarcinoma patients with R1 resection (defined as <1mm). Methods: We retrospectively collected data of patients with pancreatic adenocarcinoma who underwent adjuvant CRT (50.4-54Gy) following surgery with R1 resection between 2007-2023 in a single centre in the UK. Clinical data was collected from electronic medical records and information on radiotherapy was collected from treatment planning systems (TPS). Toxicity during and after CRT was graded with Common Terminology Criteria for Adverse Events (CTCAE). OS and PFS were measured with Kaplan-Meier curves from the time of surgery to death or disease progression or last follow up. In-field and locoregional recurrence were determined from restaging scans compared against radiotherapy field in TPS. Results: Among 33 patients included, 27 (81.8%) died within median follow-up 39 (14.8-111.4) months. All patients received adjuvant chemotherapy prior to CRT. Median OS was 42 (21.6-52.7) months and median PFS was 18.2 (15.5-28.4) months. In all but one patient, the R1 involved the posterior resection margin. Most patients (84.8%) had documented disease progression. In the majority the site of first progression was distant metastatic disease (51.5%), whilst six (18.2%) had local recurrence within the radiotherapy field. Four (12.1%) relapsed locoregionally. No statistically significance difference in OS or PFS was seen with presence of perineural or lymphovascular invasion, though analysis was limited by low number of patients. The majority of patients (72%) were node positive on pathology. Two (6.1%) patients had grade 3-4 toxicity during CRT (neutropenic and non-neutropenic sepsis). Conclusions: Our study supported acceptable safety following CRT as an adjuvant treatment in pancreatic cancer patients with R1 resection on surgery. Despite R1 resection, we observed survival outcomes with adjuvant chemotherapy and CRT somewhat above previously reported data. However the benefit of CRT after adjuvant chemotherapy remains unclear. Further evaluation is warranted to clarify which subgroups of patients benefit.