A case report of advanced pancreatic neuroendocrine carcinoma with Ki67 80%, CPS 0, and pMMR achieving durable complete response for over 7 years after combination immunotherapy

Background Pancreatic neuroendocrine carcinoma (pNEC) is a rare and aggressive malignancy. For patients with metastatic pNEC, the response to first-line chemotherapy remains unfavorable, with a median overall survival of less than one year. Furthermore, there are no standard-of-care therapeutic options following disease progression, representing a significant unmet clinical need. Case presentation This is a case report of a patient diagnosed with metastatic pNEC presenting with upper abdominal pain, testing 80% positive for the Ki67 marker, a combined positive score (CPS) of 0, and proficient mismatch repair (pMMR). Following progression after chemotherapy, the patient received combination immunotherapy, involving multi-site, multi-dose, and multi-type radiotherapies combined with programmed death 1 (PD-1), accompanied by continuous probiotic supplementation. Imaging examination revealed that the tumor completely disappeared, and the patient maintained a no-evidence-of-disease (NED) status for over seven years. Conclusion This case demonstrates that multi-site, multi-dose, and multi-type radiotherapies can more effectively reveal the heterogeneous tumor antigens, and the combined therapy of immunotherapy and probiotics may achieve sustained immune responses.