ESTRO 2023 - Abstract Book

S739

Monday 15 May 2023

ESTRO 2023

PD-0890 Efficacy of nimotuzumab plus concurrent chemoradiotherapy for unresectable esophageal cancer

Abstract withdrawn

PD-0891 From one-size-fits-all to customized treatment of gastric cancer: subgroup analyses of the CRITICS M. Verheij 1 , A. Slagter 2 , I. Caspers 3 , K. Sikorska 4 , C. van de Velde 5 , E. Meershoek-Klein Kranenbarg 5 , J. van Sandick 6 , E. Jansen 2 , H. van Laarhoven 7 , N. van Grieken 8 , A. Cats 3 1 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 2 Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands; 3 Netherlands Cancer Institute, Gastrointestinal Oncology, Amsterdam, The Netherlands; 4 Netherlands Cancer Institute, Biometrics, Amsterdam, The Netherlands; 5 Leiden University Medical Center, Surgical Oncology, Leiden, The Netherlands; 6 Netherlands Cancer Institute, Surgery, Amsterdam, The Netherlands; 7 Amsterdam University Medical Center, Medical Oncology, Amsterdam, The Netherlands; 8 Amsterdam University Medical Center, Pathology, Amsterdam, The Netherlands Purpose or Objective Current treatment strategies do not fully acknowledge biological and molecular differences at the patient and tumor level that impact on outcome. The identification of specific subgroups that respond differently to treatment may guide future trial design. Post-hoc analyses of the CRITICS gastric cancer (GC) trial were performed to reveal such subgroups. Materials and Methods The CRITICS trial randomized 788 pts to preop chemotherapy (CT) and surgery followed by either CT or chemoradiotherapy. Intention-to-treat analysis showed no difference in survival. Post-hoc analyses focused on (1) age ( ≥ 70 vs <70 yrs), (2) gender stratified by histological subtype (intestinal vs diffuse), (3) molecular subgroups (EBV+, MSI-high, EBV − /MSS). Results (1) Age: 172 (22%) were older pts. During preop CT, 77% older vs 62% younger pts developed severe toxicity (p<0.001). Similar proportions of older vs younger pts underwent curative surgery (81%) with comparable postop complications and mortality. Postop therapy started in 64% older vs 78% younger pts (p<0.001). Survival was not different. (2) Gender: Female sex was associated with distal tumor localization in both histological subtypes and younger age in diffuse type GC. (Near-)complete histopathological response was achieved in 142 (24%) males vs 17 (29%) females (p=0.464) with intestinal type and in 11 (8%) males vs 15 (16%) females (p=0.077) with diffuse type. Tumor-positive resection margins were more common in females (22%) vs males (12%) with diffuse type (p=0.032). During preop CT, severe toxicity occurred in 327 (63%) males and 184 (71%) females (p=0.015). Survival was significantly longer in pts with intestinal vs diffuse type (p<0.001), but not different between sexes. (3) Molecular subgroups: 5-yr cancer-specific survival was 69.8% in 25 pts with EBV+, 51.7% in 27 pts with MSI-high and 38.6% in 402 pts with EBV-/MSS tumors. Remarkably, the favorable outcome of MSI-high tumors was entirely attributable to women. All 3 MSI-high tumors with moderate/complete histopathological response (3/27, 11.1%) had substantial mucinous differentiation. No EBV+ tumors had a mucinous phenotype. 115/402 (28.6%) of EBV-/MSS tumors had moderate/complete response, of which 23/115 (20.0%) had a mucinous phenotype. Conclusion (1) Postoperative treatment compliance was poorer in older vs younger pts. As comparable proportions of pts underwent curative surgery, future studies should focus on neoadjuvant treatment. The ongoing CRITICS-II trial addresses this strategy. (2) Tumor-positive resection margins were higher in females vs males with diffuse type GC. CT-related toxicity was more often seen in females. Stratified for histological subtype, gender did not affect survival. Future studies should be powered and stratified for gender and histological subtype. (3) Women with MSI-high tumors had favorable outcome compared to EBV-/MSS. Major response was limited to mucinous MSI-high tumors. The mucinous phenotype might be a relevant parameter in future trials for MSI-high pts. PD-0892 Phase 2 trial of FOLFIRINOX followed by chemoradiation in locally advanced pancreatic cancer G. D'Ercole 1 , M. Fiore 2 , G.M. Petrianni 3 , P. Trecca 3 , M. Benincasa 1 , E. Ippolito 2 , D. Caputo 4 , G. Tonini 5 , R. Coppola 4 , S. Ramella 2 1 Università Campus Bio-Medico di Roma, Research Unit of Radiation Oncology, Rome, Italy; 2 Università Campus Bio-Medico di Roma, Fondazione Policlinico Universitario Campus Bio-Medico, Research Unit of Radiation Oncology, Rome, Italy; 3 Fondazione Policlinico Universitario Campus Bio-Medico, Operative Research Unit of Radiation Oncology, Rome, Italy; 4 Università Campus Bio-Medico di Roma, Fondazione Policlinico Universitario Campus Bio-Medico, Research Unit of General Surgery, Rome, Italy; 5 Università Campus Bio-Medico di Roma, Fondazione Policlinico Universitario Campus Bio-Medico, Research Unit of Medical Oncology, Rome, Italy Purpose or Objective To evaluate the margin-negative (R0) resection rate in borderline resectable and locally advanced unresectable pancreatic ductal adenocarcinoma (PDAC) after induction FOLFIRINOX followed by chemoradiotherapy (CRT). Materials and Methods We evaluated patients with locally advanced PDAC for enrolment in a single-arm, phase 2 clinical trial. Eligible patients underwent CT scan, 18FDG PET-CT scan and a staging laparoscopy to detect occult metastasis before the treatment. Patients received FOLFIRINOX regimen for 4 cycles. For patients without disease progression as detected through restaging exams, chemotherapy was followed by long-course CRT, which consisted of Volumetric Modulated Arc Therapy (VMAT) and concurrent gemcitabine at the dose of 600 mg/mq weekly. Four weeks after the completion of CRT, CT scan and PET-CT scan were performed. Surgery was considered in patients whose tumours were technically resectable. The primary objective was R0 resection rate with an alternate hypothesis of 55%. Secondary objectives included progression-free survival (PFS), overall survival (OS), local progression-free survival (LPFS), metastases free-survival (MFS), and safety. The occurrence and