GANT-like gastrointestinal pacemaker cell tumours with oncocytic features

We describe two cases of gastrointestinal stromal tumours with prominent on cocytic features. Both had features consistent with differentiation towards the interstitial cells of Cajal (CC). They were composed of nests and bund les of cells with abundant, deeply granular, eosinophilic cytoplasm. Immuno histochemical investigations revealed positivity with c-kit, vimentin and C D34 antibodies in both neoplasms. Ultrastructurally the neoplastic cells sh owed characteristic features of CC; they had synapse-like structures and de nse core cytoplasmic granules. Oncocytic features were confirmed by immunoh istochemistry using anti-mitochondrion antibody in both cases and by electr on microscopy in one case (case 1). Although the CC are frequently describe d as mitochondrion-rich cells, oncocytic changes have not previously been r eported as a feature of gastrointestinal autonomic nerve tumour (GANT)-like stromal tumours.