Gastrointestinal tract spindle cell tumors with interstitial cells of Cajal: Prevalence excluding gastrointestinal stromal tumors

Leiomyomas and schwannomas of the gastrointestinal tract (GIT) are mainly comprised of spindle-shaped tumor cells and should always be differentiated from gastrointestinal stromal tumors (GISTs). Mast/stem cell growth factor receptor Kit (KIT) and discovered on GIST-1 (DOG1) are well-known diagnostic markers for the detection of a GIST by immunohistochemical staining. The aim of the present study was to assess the prevalence and significance of spindle cell tumors of the GIT with KIT- or DOG1-positive spindle-shaped cells, presumed to be interstitial cells of Cajal (ICCs), other than GISTs. A total of 71 leiomyomas and 35 schwannomas were examined and clinicopathological information was obtained. KIT and DOG1 immunostaining was performed to determine the proportions of positive cells. Mutation screening of KIT exons 9, 11, 13 and 17, and platelet-derived growth factor receptor α (PDGFRA) exons 12 and 18 was performed in cases with a relatively high proportion of either KIT- or DOG1-positive cells. The frequency of leiomyomas and schwannomas with KIT- and DOG1-positive ICCs was 35.2% (25/71 cases) and 5.7% (2/35 cases), respectively. Among the esophageal leiomyomas with KIT- and DOG-positive ICCs (14/25; 56.0%), 5 leiomyomas involved the muscularis mucosa and 9 leiomyomas involved the muscularis propria. All gastric leiomyomas with KIT- and DOG1-positive ICCs (11/25; 44%) involved the muscularis propria. All schwannomas with an increased proportion of KIT- or DOG1-positive ICCs were of gastric origin. No KIT or PDGFRA mutations were detected in 7 leiomyomas and 2 schwannomas. In conclusion, the majority of leiomyomas and the minority of schwannomas in the GIT had a significant portion of KIT- and DOG1-positive cells. All of the tumors were located in the upper GIT, and could be present in the muscularis propria or muscularis mucosa. The tumors represented a non-neoplastic proliferation of KIT- and DOG1-positive cells in the GIT. Careful evaluation of KIT- or DOG1-positive cells in spindle cell tumors of the GIT can assist in forming the correct diagnosis by differentiation from a GIST.

Leiomyoma of the gastrointestinal tract with interstitial cells of Cajal: a mimic of gastrointestinal stromal tumor

Leiomyomas (LMs) of the gastrointestinal tract arise within the muscularis mucosae (superficial) and muscularis propria (deep). There are isolated reports of KIT-positive cells, presumed interstitial cells of Cajal (ICCs), within gastrointestinal LMs. We have encountered esophageal LMs with a high proportion of KIT-positive and DOG1-positive spindle-shaped cells, an appearance that mimicked gastrointestinal stromal tumor. Our aim was to explore the prevalence of ICCs in LMs of the gastrointestinal tract and the etiopathogenic significance of these cells in this benign neoplasm. We identified 34 esophageal LMs (28 deep, 6 superficial), 8 gastric LMs, and 5 small-bowel LMs (all lesions in muscularis propria). We performed immunohistochemical staining studies for desmin, DOG1, and KIT on these neoplasms. We also evaluated 12 superficial colonic LMs. ICCs were distinguished from mast cells on the basis of morphology (elongated and occasionally branching spindle-shaped cells) and the presence of DOG1 reactivity. Four cases were screened for mutations in PDGFRA exons 12, 14, and 18 and KIT exons 9, 11, 13, and 17. ICCs were identified in all deep esophageal LMs and constituted an average of 20% of the lesional cells; focally, these cells comprised >50% of cells. The density of these cells was significantly higher than the background muscularis propria, and hyperplasia of ICCs was not identified in the adjacent muscle. ICCs were identified in 6 of 8 gastric LMs and 1 of 5 small-bowel LMs and were entirely absent in all superficial esophageal and colonic/rectal LMs. There were no mutations in KIT or PDGFRA. ICCs are universally present in deep esophageal LMs, and thus these neoplasms could be mistaken for gastrointestinal stromal tumors, particularly on biopsy samples, an error associated with adverse clinical consequences. ICCs are also identified in gastric and intestinal LMs, albeit in a smaller proportion of cases. Colonization and hyperplasia by non-neoplastic ICCs likely account for this phenomenon.

Succinate dehydrogenase mutation underlies global epigenomic divergence in gastrointestinal stromal tumor

Gastrointestinal stromal tumors (GIST) harbor driver mutations of signal transduction kinases such as KIT, or, alternatively, manifest loss-of-function defects in the mitochondrial succinate dehydrogenase (SDH) complex, a component of the Krebs cycle and electron transport chain. We have uncovered a striking divergence between the DNA methylation profiles of SDH-deficient GIST (n = 24) versus KIT tyrosine kinase pathway-mutated GIST (n = 39). Infinium 450K methylation array analysis of formalin-fixed paraffin-embedded tissues disclosed an order of magnitude greater genomic hypermethylation relative to SDH-deficient GIST versus the KIT-mutant group (84.9 K vs. 8.4 K targets). Epigenomic divergence was further found among SDH-mutant paraganglioma/pheochromocytoma (n = 29), a developmentally distinct SDH-deficient tumor system. Comparison of SDH-mutant GIST with isocitrate dehydrogenase-mutant glioma, another Krebs cycle-defective tumor type, revealed comparable measures of global hypo- and hypermethylation. These data expose a vital connection between succinate metabolism and genomic DNA methylation during tumorigenesis, and generally implicate the mitochondrial Krebs cycle in nuclear epigenomic maintenance.