S3290 Pathologic Complete Response to Neoadjuvant FOLFIRINOX in Pancreatic Adenosquamous Carcinoma: A Rare Case Report

Introduction: Adenosquamous carcinoma of the pancreas (ASCP) is a rare and aggressive subtype of exocrine pancreatic cancer, defined histologically by ≥30% squamous differentiation alongside glandular elements. It accounts for 1–4% of pancreatic malignancies and is associated with a worse prognosis and lower chemotherapy responsiveness than pancreatic ductal adenocarcinoma (PDAC). Pathologic complete response (pCR) to neoadjuvant therapy in ASCP is exceedingly rare. This case illustrates a remarkable therapeutic outcome and its clinical implications. Case Description/Methods: A 45-year-old African American woman with no significant comorbidities presented with intermittent abdominal pain. Computed tomography imaging revealed a 5 cm mass in the pancreatic tail with encasement of the splenic vein and abutment of the celiac axis. Endoscopic ultrasound-guided fine-needle biopsy confirmed ASCP. Immunohistochemistry was positive for pankeratin, p40, CK7 (patchy), CK20, and CDX2. Tumor markers were elevated (CA 19-9: 753 U/mL; CEA: 35.7 ng/mL). Staging with chest computed tomography and diagnostic laparoscopy showed no distant metastasis (cT4N0M0, Stage III). After multidisciplinary tumor board review, the patient was started on neoadjuvant FOLFIRINOX. She completed 11 of the planned 12 cycles, discontinuing the final cycle due to fatigue and personal preference. A dose adjustment was made after cycle 4 for hepatotoxicity. Post-treatment imaging showed significant tumor regression and normalization of CA 19-9. She underwent robotic distal pancreatectomy with splenectomy. Surgical pathology demonstrated a pathologic complete response (ypT0N0), with no residual carcinoma and 0/39 lymph nodes involved. Her postoperative course was uneventful, and surveillance imaging and labs remained negative for recurrence at 9 months. Discussion: This case highlights a rare pathologic complete response in ASCP following extended neoadjuvant FOLFIRINOX. It underscores the potential of aggressive multimodal therapy and multidisciplinary care in borderline resectable pancreatic cancer. While ASCP has historically carried a poor prognosis, selected patients may achieve excellent outcomes with personalized treatment strategies. Further research is needed to identify predictors of response in this challenging malignancy.