Phase II trial of maximal ablative irradiation because of encasement (MAIBE) for patients with potentially resectable locally advanced pancreatic cancer.

Abstract

710 Background: For patients with localized but not immediately resectable pancreatic adenocarcinoma (PDAC), the role for local therapy remains undefined. Phase II MAIBE trial studied ablative radiation (A-RT) followed by consideration of surgery for patients with locally advanced pancreatic cancer (LAPC) who remain unresectable after induction chemotherapy. Methods: Participants with histologically confirmed PDAC judged unresectable by multidisciplinary review using NCCN definition after completing 3-6 months of mFOLFIRINOX (FFX) or Gemcitabine/Nab-paclitaxel (GN) were eligible. They received hypofractionated A-RT (either 67.5Gy in 15 fractions or 75Gy in 25 fractions based on anatomy) with concurrent capecitabine followed by consideration of resection within 1-3 months. Primary endpoints included resectability (80% power to detect resectability improvement from 15% in historical controls to 30% with α = 0.05) and overall survival (OS) from A-RT. Secondary endpoints included safety of surgical resection after ablative RT using 90-day Clavien-Dindo Classification of adverse events (AE). Results: Between 6/2018 and 4/2022, 47 eligible participants underwent A-RT. Median age was 67 (range, 50-80) years, 24 (51%) were male with a median tumor size of 3.95 (1.6 – 8.3) cm and CA19-9 of 92 ( < 1-1601) U/mL. Forty-four patients (94%) received at least 1 cycle of FFX with a median duration of chemotherapy (FFX or GN) of 3.5 months (1.0 – 9.4). Sixteen (34%) underwent a laparoscopy and 12 (26%) underwent a resection (Pancreaticoduodenectomy, N = 11; distal pancreatectomy, N = 1) at a median time of 3.2 months (1.9-16.9 months) from start of A-RT. The rate of resection satisfied our prespecified boundary of 11. R0 rate was 58.3%. Two-year OS from A-RT for the entire cohort was 38.9% (95% CI, 21.9 – 55.6%), including 37.1% (18.5 - 55.8%) in non-surgical and 39.4% (7.0- 72.1%) in surgical groups. There were no deaths within 90 days of surgery and 9 surgical AEs were recorded in 6 participants, including grade 1 (n = 1), grade 2 (n = 5), grade 3 (n = 2) and grade unknown (n = 1). Conclusions: In patients with LAPC and no metastatic disease after 3-6 months of chemotherapy, A-RT results in a favorable rate of resection without excess surgical toxicity. Promising 2-year OS rates were noted in both resected and non-resected patients. Clinical trial information: NCT03523312 .