Laparoscopically resected appendiceal dual tumor composed of goblet cell carcinoma and low-grade mucinous neoplasm: a case report and literature review.

Dual tumors, comprising two different types of tumor, are uncommon pathologic findings. Appendiceal goblet cell carcinoid is an unusual and unique subtype of primary appendiceal neuroendocrine tumor defined by the World Health Organization, showing hybrid epithelial-neuroendocrine features. Low-grade mucinous neoplasms are also rare appendiceal neoplasms. However, the relationship between these two types of tumors is not well known. We present the case of a 46-year-old woman with a 5 cm appendiceal cystic tumor that was incidentally detected on abdominal computed tomography. She showed no abdominal symptoms, enlarged lymph nodes, or obvious distant metastases. Laparoscopic ileocecal resection was performed without complications or tumor injury. No disseminated lesions or mucus accumulation was found in the abdominal cavity during the operation. Pathologic examination revealed low-grade mucinous tumor cells lining the cystic mucosal cavity and a chromogranin A-positive goblet cell carcinoid near the mucinous cell components. As there was no mixture of the two cell types, the tumor was suspected of a collision tumor. Although reports on appendiceal collision tumors are limited, these two tumor types might arise from different types of progenitor cells. Furthermore, the laparoscopic approach, which allows for a more detailed and safer observation of the entire abdominal cavity, could be useful for accurate staging and treatment decisions in mucinous appendiceal tumors at risk of intraperitoneal mucinous dissemination and peritoneal pseudomyxoma. Accumulation of case reports of such dual tumors and analysis at the molecular and cellular level are necessary to elucidate their pathogenesis and development.