A Rare Case of Collision Tumor at the Periampullary Region.

Collision tumors are rare neoplasms composed of two histologically distinct components without a transitional zone. Only nine cases involving periampullary adenocarcinoma and neuroendocrine tumor (NET) have been reported. A 55-year-old male presented with recurrent fever and jaundice. Imaging and biopsy revealed a periampullary lesion diagnosed as tubule-villous adenoma with high-grade dysplasia. He underwent pylorus-preserving pancreatoduodenectomy. Histology revealed moderately differentiated intestinal-type adenocarcinoma (pT2N1) with regional lymph node metastasis. Additionally, a 2-mm well-differentiated NET was found 2.5 cm proximal to the primary tumor, also with nodal metastasis. Immunohistochemistry confirmed distinct lineages, fulfilling the criteria for a collision tumor. This case represents a rare periampullary collision tumor with both adenocarcinoma and NET components showing independent lymph node metastases. The absence of transitional zones rules out MiNEN. This report underscores the importance of thorough pathological assessment and adds to the limited literature on the behavior and prognosis of periampullary collision tumors.