Clinical Characteristics and Treatment Courses of Exceptional Long-Term Survivors After Multimodal Therapy Including Proton Beam Therapy for Borderline Resectable and Locally Advanced Pancreatic Cancer: A Retrospective Case Series.

Background Despite advances in multimodal treatment, the prognosis of borderline resectable pancreatic cancer (BR-PC) and unresectable locally advanced pancreatic cancer (UR-LAPC) remains poor. We performed a descriptive retrospective analysis of 10 exceptional long-term survivors who survived more than five years following proton beam therapy (PBT). Methods Among 112 patients with BR-PC or UR-LAPC who underwent definitive PBT at our institution, 10 patients who survived for more than five years were retrospectively analyzed. Clinical characteristics, treatment courses, adverse events, and outcomes were reviewed. Results The median age was 64.5 years (range, 50-74), and two patients were men and eight were women. Six patients had BR-PC and four had UR-LAPC. The median pretreatment CA19-9 level was 78.2 U/mL (range, <2.0-837). Three patients received induction chemotherapy for less than one month. All patients received PBT at 67.5 Gy (RBE) in 25 fractions with concurrent gemcitabine and hyperthermia, followed by maintenance chemotherapy. The median observed follow-up/survival duration was 76 months (range, 60-115 months). Three patients underwent conversion surgery following PBT, with pathological complete response achieved in two patients. Among the seven patients who did not undergo surgery, five experienced disease progression, whereas two remained progression-free throughout follow-up. At the time of analysis, eight of the 10 patients were alive. Conclusions Long-term survival beyond five years was observed in a subset of patients with BR-PC or UR-LAPC treated with multimodal therapy including PBT. Clinical courses varied substantially among these exceptional survivors, including both patients who underwent conversion surgery and those managed without surgical resection. Further studies are needed to clarify factors associated with long-term survival.