GASTROINTESTINAL PACEMAKER CELL TUMOR (GIPACT) - GASTROINTESTINAL STROMAL TUMORS SHOW PHENOTYPIC CHARACTERISTICS OF THE INTERSTITIAL-CELLS OF CAJAL

The interstitial cells of Cajal (ICC) form a complex cell network with in the gastrointestinal tract wall where the function as a pacemaker s ystem. Expression of the kit proto-oncogene is essential for the devel opment of this system. The aim of our study was to examine the hypothe sis that gastrointestinal stromal tumors differentiate toward cells wi th an ICC phenotype. Ultrastructurally, 58 stromal tumors were charact erized and found to share many features with ICC. Seventy-eight stroma l tumors were immunophenotyped, particularly with regard to the kit re ceptor. AU 78 tumors revealed strong, homogeneous immunoreactivity for the kit receptor as did ICC of adjacent and control gastrointestinal walls. Focal hyperplasia and hypertrophy of kit receptor positive cell s were also observed in the gastrointestinal wall adjacent to the tumo rs. CD34 immunoreactivity observed in interstitial cells surrounding A uerbach's ganglia suggests that a subpopulation of ICC is CD34 positiv e and may explain why 56 of 78 stromal tumors were CD34 positive. Thir ty control tumors, including gastrointestinal leiomyomas and leiomyosa rcomas, were all negative for the kit receptor, We conclude that gastr ointestinal stromal tumors show striking morphological and immunopheno typic similarities with ICC and that they may originate from stem cell s that differentiate toward a pacemaker cell phenotype. We propose tha t the noncommittal name ''gastrointestinal stromal tumor'' be replaced by gastrointestinal pacemaker cell tumor.