Pancreatobiliary Adenocarcinoma in a Gastric Duplication Cyst: A Doubly Rare Diagnosis.

Gastric duplication cyst (GDC) is a rare congenital abnormality and the development of malignant transformation in these lesions is even rarer, with only few reported cases worldwide to date. We hereby report an additional case of cancer arising from a GDC in a 54-year-old male. The patient's chief complaints were abdominal pain and significant weight loss. Computed tomography and endoscopy ultrasonography (EUS) revealed a nodular formation with a cystic component, localized in the great gastric curvature and invading the spleen and left adrenal gland. The biopsy from EUS was inconclusive. After exploratory laparotomy, the patient was submitted to an en-bloc resection with partial gastrectomy, splenectomy and left adrenalectomy. Histopathologic examination revealed a cystic mass non-communicating with the gastric wall. Immunohistochemistry staining showed a moderately differentiated pancreatobiliary adenocarcinoma within a duplication cyst with lymphovascular and perineural invasion. The patient was proposed to adjuvant systemic treatment, however, after few months he developed metachronous metastasis. To our knowledge, this is the first case of adenocarcinoma with pancreatobiliary differentiation arising from a gastric duplication cyst.