Conversion therapy followed by curative resection in a patient with ACTH-secreting pancreatic neuroendocrine tumor G3: a case report.

Background: Pancreatic neuroendocrine tumors (pNETs) with ectopic adrenocorticotropic hormone (ACTH) production are uncommon, highly aggressive, and carry a dismal prognosis. Early nonspecific symptoms often delay diagnosis, and treatment strategies remain controversial. For patients with locally advanced pNETs, conversion therapy has only rarely been reported and remains a sparingly applied strategy. Case presentation: A 37-year-old woman presented with a six-month history of progressive swelling in both lower extremities and her face. Further workup confirmed ACTH-dependent Cushing syndrome. CT and MRI identified a 5.7 × 2.8 cm lesion in the pancreatic body/tail that invaded the left adrenal gland and splenic vessels, accompanied by retroperitoneal lymph node spread. Biopsy results indicated a G3 pNET. Given the borderline resectable status due to local advancement, she received conversion therapy comprising a long-acting somatostatin analogue followed by CapTem chemotherapy. After three months of neoadjuvant treatment, imaging showed modest primary tumor shrinkage and marked reduction of lymph node size, reflecting successful downstaging. Subsequently, she underwent distal pancreatectomy with splenectomy, left adrenalectomy, and lymph node dissection, achieving R0 resection. Final pathology confirmed a G3 pNET (Ki-67 30%-40%) with positive SSTR2 and ACTH immunostaining. Although the patient eventually experienced disease progression and succumbed to COVID-19 infection 37 months after initial diagnosis, this case illustrates that conversion therapy can render an initially borderline resectable high-grade pNET amenable to curative resection. Conclusion: This report underscores the aggressive trajectory of ACTH-secreting pNET G3 and suggests the potential utility of conversion therapy. Further studies are needed to validate this approach.