Collision Tumor in the Stomach: Tubular Gastric Adenocarcinoma With Metastatic Adrenocortical Carcinoma—A Rare Encounter on an Endoscopic Biopsy

Collision tumors are rare neoplastic entities characterized by the coexistence of two histologically distinct malignancies within the same organ, separated by an abrupt interface without transitional morphology. Gastric collision tumors are exceptionally uncommon, and their endoscopic and pathological features remain poorly defined. Here, we report a gastric collision tumor composed of a primary gastric tubular adenocarcinoma and metastatic adrenocortical carcinoma. Adrenocortical carcinoma is a highly aggressive malignancy characterized by marked local invasiveness and a strong propensity for distant metastasis, most commonly involving solid organs. In contrast, metastasis to hollow visceral organs is very rare, with gastric involvement reported only once previously, where it mimicked a primary gastric malignancy. To date, gastric collision tumors composed of a primary gastric carcinoma and a metastatic extra-gastric malignancy have not been described. This report highlights the diagnostic challenges of atypical gastric lesions and underscores the importance of careful endoscopic, histopathological, and immunohistochemical evaluation in identifying collision tumors, as accurate recognition directly impacts staging, management, and prognosis.