Sporadic diffuse segmental interstitial cell of Cajal hyperplasia harbouring two gastric gastrointestinal stromal tumours (GIST) mimicking hereditary GIST syndromes

INTRODUCTION: Gastrointestinal stromal tumours (GISTs) are thought to derive from or differentiate towards the interstitial cells of Cajal (ICC) as most demonstrate a similar immunoprofile: CD117+, CD34+ and DOG1+. ICC hyperplasia refers to KIT-expressing microscopic spindle cell proliferations involving the myenteric plexus. CASE REPORT: 74 year-old male presented with a 5-year history of heartburn and dysphagia. Imaging revealed a 4 cm GIST in the gastric fundus. Pathology of the resected specimen revealed diffuse segmental ICC hyperplasia harbouring two macroscopic GISTs and a ‘tumorlet’. A mutation in c-KIT exon 11 was detected in both the solid and the diffuse components. DISCUSSION: ICC hyperplasia can occur either as a sporadic focal lesion or in a syndromic setting, known to predispose to multiple GIST tumours at different sites. The majority of cases of sporadic ICC hyperplasia previously reported were of localised type. The hereditary form is mostly caused by germline mutations in c-KIT and PDGFRA or in patients with NF-1 andpresents as a diffuse hyperplasia, usually with a confluent, nodular or multifocal growth pattern. CONCLUSION: We describe a diffuse form of sporadic ICC hyperplasia harbouring multifocal GISTs, mimicking diffuse ICC hyperplasia in hereditary GIST syndromes. Detection of somatic c-KIT exon 11 mutation ruled out a hereditary disorder.