Incorporating stereotactic body radiation therapy for inoperable pancreatic cancer.

Abstract

656 Background: The management of inoperable pancreatic cancer (PC) is controversial. We sought to compare local progression (LP) for inoperable PC managed with chemotherapy (CHT) and/or stereotactic body radiation therapy (SBRT). Methods: This single-institution retrospective review analyzed 94 patients diagnosed with locally advanced (LA), medically inoperable, or metastatic PC between 2014 and 2022. Patients received CHT alone, sequential (seq) CHT + SBRT, or SBRT alone. The primary endpoints were LP and intervention due to local progression (ILP) from start of treatment. Obstructive symptoms needing intervention, percutaneous endoscopic gastrostomy tube, gastrojejunostomy, or bleeding needing transfusion were considered ILP. Primary tumor growth on imaging or ILP were defined as LP. Fine-Gray regression models with treatment received considered a time-varying covariate were used to compare ILP and LP between treatment groups where death without LP was treated as a competing risk adjusting for ECOG, stage, age and year of diagnosis. In the subgroup of patients who received SBRT, patients were stratified at the median time between diagnosis and receipt of SBRT, and risk of ILP and LP was compared between the groups using cause-specific cumulative incidence functions. Results: Of 94 patients, 51 had CHT alone, 21 received seq CHT + SBRT, and 22 had SBRT alone. The median year of diagnosis was 2019 (range, 2014 - 2022). The median ECOG was 1 with worse ECOG in SBRT alone and seq CHT + SBRT groups (p = 0.012). There were more LA or metastatic cases in the CHT (78%) and seq CHT + SBRT groups (67%) compared to the SBRT group (23%) [p < 0.001]. The median SBRT dose was 36Gy (range, 25 – 40Gy) in 5 fractions. Rates of LP and ILP were higher for CHT alone (68.6%, 39.2%) compared to seq CHT + SBRT (42.9%, 38.1%) or SBRT alone (18.2%, 4.5%) [p < 0.001; p = 0.004]. Higher rate of ILP associated with an increasing year of diagnosis (HR = 2.03, p < 0.005) and younger age of diagnosis (HR = 0.922, p = 0.011). The median time to SBRT was 116 days. Early (< 116 days) vs late SBRT LP rates differed (ILP: 4.8% vs 30%, LP: 14.3% vs 40%). Cause-specific cumulative incidence functions showed that death without LP favored early vs late SBRT (p = 0.009). Additionally, death without ILP favored early vs late SBRT (p=0.011). Conclusions: LP rates are high among patients with inoperable PC. SBRT for inoperable PC provides reasonable local control. Early SBRT reduces the need for ILP before death compared with late SBRT. Further investigation into the role of SBRT for inoperable PC is necessary. [Table: see text]