Collision tumor of the appendix with concomitant cecal adenocarcinoma: A case report and literature review.

Introduction: Collision tumors of the appendix are rare tumors consisting of two distinct pathologies arising from different cell lines simultaneously. The most common type is the coexistence of a neuroendocrine tumor (NET) with a low-grade appendiceal mucinous neoplasm (LAMN). We report a unique case of appendiceal collision tumor with synchronous cecal intra-mucosal carcinoma and pulmonary sarcoidosis.

Case Presentation: A 57-year-old man presented to the clinic with vague abdominal pain. Upon investigation, a colonoscopy showed a large cecal mass, and a computed tomography scan showed a polypoid cecal mass, a dilated, fluid-filled appendix, multiple bi-lobar lung nodules, and enlarged mediastinal and hilar lymph nodes (LN). Following discussion in a multi-disciplinary team tumor board meeting, the patient underwent laparoscopic right hemicolectomy and mediastinoscopy with mediastinal LN biopsy. His postoperative hospital stay was uneventful. Histopathology revealed a cecal tubulovillous adenoma with intra-mucosal carcinoma. A collision tumor of the appendix was found, including an in situ LAMN and a < 5 mm NET. The mediastinal LN showed sarcoidosis. There was no evidence of recurrence after a two-year follow-up.

Discussion: Previous reports of appendicular collision tumors show high variability in the presentation and management. While some present with acute appendicitis, others may have a subacute or atypical presentation. Management ranges from appendectomy to cytoreductive surgery and hyperthermic intraperitoneal chemotherapy, depending on the tumor stage.

Conclusion: Collision tumors of the appendix are rare, with highly variable presentation and management. There are no clear management or surveillance guidelines, given their rarity. Thus, treatment should be individualized.