Synchronous GIST with osteoclast-like giant cells and a well-differentiated neuroendocrine tumor in Ampula Vateri: Coexistence of two extremely rare entities

Mesenchymal tumors of the gastrointestinal system with variable histopathological appearances and constant expression of CD117 are known as gastrointestinal stromal tumors (GISTs). Neuroendocrine tumors may be seen in the gastrointestinal system and other organ systems of the body. We report a 44-year-old male patient with a 6.5×3×6 cm mass located in the Ampulla of Vater. Histopathologic examination revealed a GIST with a marked nuclear pleomorphism and a high mitotic rate, and that was rich in osteoclast-like giant cells (OGC). Immunohistochemically, GIST was positive for CD117, while OGCs were negative for CD117 and positive for CD68 and α1-antitrypsin. There was also found a well-differentiated neuroendocrine tumor near the GIST, in the serosal aspect of the duodenum at the point of the Ampulla of Vater. This second tumor was 20 mm in diameter, and was relatively well circumscribed with few glands invading the GIST. This tumor was positive for synaptophysin and chromogranin. Neither mitosis nor vascular invasion was observed. The patient had no familial history or clinical manifestations of neurofibromatosis. This case presents the unique synchronous existence of two extremely rare entities, a GIST with OGC and a well-differentiated neuroendocrine tumor, both located in the Ampulla of Vater.