Collision Tumour

(1) A generic term for the extremely rare merging of 2 originally separate—primary—tumours from 2 organs, most often seen at the oesophagogastric junction, where a squamous cell carinoma of oesophageal origin collides with a gastric adenocarcinoma; diagnosis of a collision tumour requires that the 2 tumours be histologically distinct
(2) A neuroendocrine (carcinoid) tumour characterised by discrete populations of neoplastic neuroendocrine cells and glands