Interstitial cell of Cajal (ICC) hyperplasia has been documented in conditions 
associated with multiple gastrointestinal stromal tumours (GISTs) (familial GIST 
syndromes, Carney's triad and von Recklinghausen's disease) and rarely in the 
vicinity of sporadic GISTs. The incidence of sporadic ICC hyperplasia and the 
so-called seedling leiomyoma (SLM) of the lower oesophagus has not been studied 
in the KIT era. In a retrospective review of 77 consecutive, routinely processed 
oesophagogastric resection specimens for distal oesophageal carcinoma, we found 
foci of ICC hyperplasia in 7 of 77 (9.1%) cases and foci of SLM in 17 of 77 
(22%) cases. Two types of ICC hyperplasia were recognized: a non-circumscribed 
type and a nodular expansile type with peripherally compressed myenteric neural 
tissues. All cases of ICC hyperplasia were vimentin+/CD34+/CD117+. SLMs were 
desmin+/vimentin(-)/CD34(-)/CD117(-), similar to smooth muscles of the gut wall. 
In a prospective study of 32 non-carcinomatous specimens from age-matched 
patients (mostly autopsy cases), we found SLMs in only one case, but we were 
unable to detect ICC hyperplasia in any of the cases. We concluded that sporadic 
KIT-positive spindle-cell hyperplasia and SLMs were unexpectedly common in 
distal oesophageal specimens harbouring carcinomas. The possible mechanisms 
leading to the development of these putative precursor lesions will be 
discussed.