Interstitial Cells Of Cajal Hyperplasia Research Articles

A154 PRIMARY APPENDICEAL GASTROINTESTINAL STROMAL TUMOR (GIST) IN A PATIENT WITH DELAYED APPENDICITIS: CASE PRESENTATION AND LITERATURE REVIEW

Abstract Background Gastrointestinal stromal tumors (GISTs) are uncommon neoplasias, arising from mesenchymal tissue in the gastrointestinal tract. However, primary appendiceal GISTs (PA-GISTs) are rare, with less than 27 cases reported to date. Although treatable with neoadjuvant chemotherapy and subsequent resection, GISTs of the appendix can initially present with appendicitis-like symptoms, and are often treated as acute appendicitis (AA) due to initial misdiagnosis. A 75-year-old man presented to the emergency department of Brightshores Health System (BSHS) with right upper abdominal pain progressing to the right lower quadrant. He was referred to our surgical service, and his condition was treated as delayed appendicitis. Aims 1. To raise awareness of GIST as a distinct diagnostic possibility in patients presenting with acute appendicitis (AA)-like symptoms. 2. To assess whether delayed appendectomy has an impact in the overall disease outcome for PA-GIST. Methods A rare case of PA-GIST was found after a retrospective review of all appendectomies performed at BSHS for appendicitis with or without neoplasia in the last 11 years. To our surprise, we uncovered a rare case PA-GIST. Comprehensive chart review was performed. Results A 75-year-old man presenting with a 5-day history of right upper and lower abdominal pain was clinically diagnosed with AA. CT abdomen and ultrasound showed probable appendicitis with phlegmon, distal tip inflammation, no abcess and mild left hydronephrosis. After initial antibiotics and colonoscopy, the patient underwent interval appendectomy. Pathology revealed no AA, a low-grade GIST with focal interstitial cell of Cajal hyperplasia of the distal appendix and positive margin. Six weeks later, cecectomy showed no clinicopathologic evidence of residual PA-GIST. Literature review revealed 27 other PA-GIST tumors to date. Twenty three were found incidentally through imaging, colonoscopy, or surgery. Four cases involved patients presenting with AA symptoms. Our patient was among those presenting with AA symptoms, but with no histological evidence of appendicitis in the delayed appendectomy specimen. Consistent with 25/27 cases, our patient’s GIST displayed spindle morphology, ampersand:003C5cm in size, and without atypia, mitosis, or necrosis. Conclusions PA-GISTs tumors are rare, with only 28 cases reported to date, including ours. Some PA-GIST tumors are found incidentally in patients that present with symptoms of AA. Although there is no concensus opinion for optimal treatment of PA-GIST, delayed appendectomy followed by cecectomy have proven to be an acceptable treatment for our patient with no evidence of recurrent or metastatic disease after 6.5 years on follow up by clinical and endoscopic surveilance. Funding Agencies None

A smooth muscle-derived, Braf-driven mouse model of gastrointestinal stromal tumor (GIST): evidence for an alternative GIST cell-of-origin.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumor of the gut. GISTs are thought to arise solely from interstitial cells of Cajal (ICC), a KIT-positive population that controls gut motility. Activating gain-of-function mutations in KIT and PDGFRA are the most frequent driver events, and most of these tumors are responsive to the tyrosine kinase inhibitor imatinib. Less common drivers include mutant BRAFV600E and these tumors are resistant to imatinib. A mouse model of GIST was recently reported using Etv1, the master transcriptional regulator of ICC-intramuscular (IM) and ICC-myenteric (MY), to induce mutant Braf expression. ICC hyperplasia was observed in Etv1CreERT2 ;BrafLSL-V600E/+ mice but loss of Trp53 was required for development of GIST. We identified previously expression of the pan-ErbB negative regulator, LRIG1, in two distinct subclasses of ICC [ICC-deep muscular plexus (DMP) in small intestine and ICC-submucosal plexus (SMP) in colon] and that LRIG1 regulated their development from smooth muscle cell progenitors. Using Lrig1CreERT2 to induce BrafV600E , we observed ICC hyperplasia beyond the confines of ICC-DMP and ICC-SMP expression, suggesting smooth muscle cells as the cell-of-origin. To examine this possibility, we selectively activated BrafV600E in smooth muscle cells. Myh11CreERT2 ;BrafLSL-V600E/+ mice developed not only ICC hyperplasia but also GIST and in the absence of Trp53 disruption. In addition to providing a simpler model for mutant Braf GIST, these results provide conclusive evidence for smooth muscle cells as an alternative cell-of-origin for GIST. © 2020 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Covering the Cover

Covering the Cover

Hyperglycemia Increases Interstitial Cells of Cajal via MAPK1 and MAPK3 Signaling to ETV1 and KIT, Leading to Rapid Gastric Emptying

Depletion of interstitial cells of Cajal (ICCs) is common in diabetic gastroparesis. However, in approximately 20% of patients with diabetes, gastric emptying (GE) is accelerated. GE also occurs faster in obese individuals, and is associated with increased blood levels of glucose in patients with type 2 diabetes. To understand the fate of ICCs in hyperinsulinemic, hyperglycemic states characterized by rapid GE, we studied mice with mutation of the leptin receptor (Leprdb/db), which in our colony had accelerated GE. We also investigated hyperglycemia-induced signaling in the ICC lineage and ICC dependence on glucose oxidative metabolism in mice with disruption of the succinate dehydrogenase complex, subunit C gene (Sdhc). Mice were given breath tests to analyze GE of solids. ICCswere studied by flow cytometry, intracellular electrophysiology, isometric contractility measurement, reverse-transcription polymerase chain reaction, immunoblot, immunohistochemistry, enzyme-linked immunosorbent assays, and metabolite assays; cells and tissues were manipulated pharmacologically and by RNA interference. Viable cell counts, proliferation, and apoptosis were determined by methyltetrazolium, Ki-67, proliferating cell nuclear antigen, bromodeoxyuridine, and caspase-Glo 3/7 assays. Sdhc was disrupted in 2 different strains of mice via cre recombinase. In obese, hyperglycemic, hyperinsulinemic female Leprdb/db mice, GE was accelerated and gastric ICC and phasic cholinergic responses were increased. Female KitK641E/+ mice, which have genetically induced hyperplasia of ICCs, also had accelerated GE. In isolated cells of the ICC lineage and gastric organotypic cultures, hyperglycemia stimulated proliferation by mitogen-activated protein kinase 1 (MAPK1)- and MAPK3-dependent stabilization of ets variant 1-a master transcription factor for ICCs-and consequent up-regulation of v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) receptor tyrosine kinase. Opposite changes occurred in mice with disruption of Sdhc. Hyperglycemia increases ICCs via oxidative metabolism-dependent, MAPK1- and MAPK3-mediated stabilization of ets variant 1 and increased expression of KIT, causing rapid GE. Increases in ICCs might contribute to the acceleration in GE observed in some patients with diabetes.

Leiomyoma of the Gastrointestinal Tract With Interstitial Cells of Cajal

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.

163 Hyperglycemia-Induced Hyperplasia of Interstitial Cells of Cajal (ICC) and ICC Stem Cells (ICC-SC) Is Associated With Accelerated Gastric Emptying in Obese Diabetic LeprDb/Db Mice

Background & Aims: ICC depletion is the most common cellular change in diabetic gastroparesis. However, in up to 22% of diabetic patients with gastric symptoms, gastric emptying (GE) is accelerated, rather than delayed. The fate of ICC in these patients is unclear. Previously we reported ICC and ICC-SC hyperplasia in hyperinsulinemic, diabetic Lepr mice. Here, we studied the relationship between GE of solids and ICC/ICC-SC numbers, and investigated the contribution of insulin/IGF1-dependent Kit ligand (Kitl) expression and hyperglycemia-induced ERK MAPK activation to ICC/ICC-SC hyperplasia. Methods: Lepr (n=32) and agesexand strain-matched controls (n=30) were studied 13-65 weeks after the onset of diabetes. ICC and ICC-SC were quantified by flow cytometry. Serum insulin was measured by enzyme immunoassay. Oxidative stress was determined by measuring serum malondialdehyde (MDA) and gastric 8OHdG. GE of solids was analyzed by 13C breath test. Gene expression was studied by qRT-PCR and WB. Effects of high glucose were investigated in murine gastric ICC primary cultures, a conditionally immortalized cell line derived from murine gastric ICC (ICL2A), and in an ICC-SC line isolated from the mouse stomach (2XSCS2F10). ERKMAPK signaling was evaluated byWB and pharmacological inhibition of MAPKK with PD98059. Cell proliferation and apoptosis were determined byMTS assay andCaspase Glo-3/7 assay, respectively. Results: Leprmice had significantly higher blood glucose (median[IQR]: 515[462;577] vs. 124[115;134] mg/dL; P,0.001) and serum insulin levels. Serum MDA and gastric 8OHdG were moderately increased (2.4and 2.2-fold, respectively, P,0.001). In Lepr mice, ICC and ICC-SC increased 2.0±0.1-fold (P,0.001) and 1.5±0.3-fold (P,0.05), respectively, and GE was accelerated (T1/2: 67±10 vs. 100±11 min; P,0.05). GE was similarly accelerated in Kit mice with generalized ICC hyperplasia due to an activating Kit mutation. In Lepr mice, total/soluble Kitl mRNA and Kitl protein were reduced. High glucose (500 mg/dL) significantly increased the numbers of primary ICC and stimulated proliferation and ERK MAPK phosphorylation in ICL2A and 2XSCS2F10 cells. PD98059 (20 μM) inhibited cell proliferation induced by high glucose without affecting basal proliferation. In contrast, osmotic stress induced by mannitol had no effect on ICC numbers, cell proliferation and ERK MAPK phosphorylation. ICC and ICC-SC were resistant to apoptosis induced by hyperglycemia at levels seen in Lepr mice. Conclusions: In the absence of major oxidative stress, hyperglycemia induces ICCSC and ICC hyperplasia via the ERK MAPK pathway even in the presence of reduced Kitl signaling. ICC hyperplasia, in turn, leads to accelerated GE and may contribute to gastric symptoms in a subset of diabetic patients. Grant support: NIH DK58185, DK68055.

Use of potassium channel tetramerization domain-containing 12 as a biomarker for diagnosis and prognosis of gastrointestinal stromal tumor

Previously, we showed that the expression of potassium channel tetramerization domain-containing 12 (KCTD12), which was discovered by a proteomics approach, is associated with high-risk behavior of gastrointestinal stromal tumors (GISTs). Here, we examined the distribution and expression of this protein by immunostaining with a commercially available polyclonal KCTD12 antibody in GISTs (n = 64) and other types of malignancy (n = 168) to clarify its diagnostic and clinical significance. Diffuse KCTD12 immunoreactivity was found in most GISTs (52 cases; 81%). KCTD12 expression was observed primarily in vascular endothelial cells, Purkinje cells of the cerebellum, and some neurons scattered throughout the cerebral cortex. KCTD12 was absent from not only the interstitial cells of Cajal but also interstitial cells of Cajal hyperplasia that was encountered incidentally in colon diverticulitis. KCTD12 immunostaining was also seen in malignant peripheral nerve sheath tumors (2/10 cases; 20%), synovial sarcomas (2/10; 20%), solitary fibrous tumor (1/8; 13%), angiosarcoma (1/7; 14%), and colon adenocarcinoma (1/24; 4%). In survival analyses, the 5-year recurrence-free survival rate of patients without KCTD12 expression was only 16.7% compared with 95.6% in those with KCTD12 expression (P < .0001). Ki-67 and KCTD12 were significant predictors of recurrence-free survival, and KCTD12 expression provided additional information about recurrence-free survival after accounting for Ki-67 status. Overall, KCTD12 expression was specific for GISTs from neoplastic and nonneoplastic adult tissues other than brain and served as a predictor of GIST recurrence. These findings suggest that KCTD12 is a useful and reliable biomarker for both the diagnosis and prognosis of GIST.

Imatinib resistance and microcytic erythrocytosis in a Kit V558Δ;T669I/+ gatekeeper-mutant mouse model of gastrointestinal stromal tumor

Most gastrointestinal stromal tumors (GISTs) harbor a gain-of-function mutation in the Kit receptor. GIST patients treated with the tyrosine kinase inhibitor imatinib frequently develop imatinib resistance as a result of second-site Kit mutations. To investigate the consequences of second-site Kit mutations on GIST development and imatinib sensitivity, we engineered a mouse model carrying in the endogenous Kit locus both the Kit(V558Δ) mutation found in a familial case of GIST and the Kit(T669I) (human KIT(T670I)) "gatekeeper" mutation found in imatinib-resistant GIST patients. Similar to Kit(V558/+) mice, Kit(V558;T669I/+) mice developed gastric and colonic interstitial cell of Cajal hyperplasia as well as cecal GIST. In contrast to the single-mutant Kit(V558/+) control mice, treatment of the Kit(V558;T669I/+) mice with either imatinib or dasatinib failed to inhibit oncogenic Kit signaling and GIST growth. However, this resistance could be overcome by treatment of Kit(V558;T669I/+) mice with sunitinib or sorafenib. Although tumor lesions were smaller in Kit(V558;T669I/+) mice than in single-mutant mice, both interstitial cell of Cajal hyperplasia and mast cell hyperplasia were exacerbated in Kit(V558;T669I/+) mice. Strikingly, the Kit(V558;T669I/+) mice developed a pronounced polycythemia vera-like erythrocytosis in conjunction with microcytosis. This mouse model should be useful for preclinical studies of drug candidates designed to overcome imatinib resistance in GIST and to investigate the consequences of oncogenic KIT signaling in hematopoietic as well as other cell lineages.

Selected Unusual Tumors of the Stomach

Several unusual stomach tumors have been recently described. In addition, some tumors that are often encountered in other sites may rarely occur as primary gastric tumors. The diagnostic surgical pathologist needs to be aware of some of these lesions to prevent misdiagnosis. This overview discusses the key clinical features, pathology, immunohistochemistry, and relevant molecular findings of multiple minute gastrointestinal stromal tumors and interstitial cell of Cajal hyperplasia, nerve sheath tumors (schwannoma and perineurioma), gastroblastoma, granular cell tumor, glomus tumor, plexiform angiomyxoid myofibroblastic tumor, and primary clear cell sarcoma of the gastrointestinal tract that occur as primary gastric neoplasms.

ETV1 is a lineage survival factor that cooperates with KIT in gastrointestinal stromal tumours

Gastrointestinal stromal tumour (GIST) is the most common human sarcoma and is primarily defined by activating mutations in the KIT or PDGFRA receptor tyrosine kinases1,2. KIT is highly expressed in interstitial cells of Cajal (ICCs)—the presumed cell of origin for GIST—as well as in hematopoietic stem cells, melanocytes, mast cells and germ cells2,3. Yet, families harbouring germline activating KIT mutations and mice with knock-in Kit mutations almost exclusively develop ICC hyperplasia and GIST4–7, suggesting that the cellular context is important for KIT to mediated oncogenesis. Here we show that the ETS family member ETV1 is highly expressed in the subtypes of ICCs sensitive to oncogenic KIT mediated transformation8, and is required for their development. In addition, ETV1 is universally highly expressed in GISTs and is required for growth of imatinib-sensitive and resistant GIST cell lines. Transcriptome profiling and global analyses of ETV1-binding sites suggest that ETV1 is a master regulator of an ICC-GIST-specific transcription network mainly through enhancer binding. The ETV1 transcriptional program is further regulated by activated KIT, which prolongs ETV1 protein stability and cooperates with ETV1 to promote tumourigenesis. We propose that GIST arises from ICCs with high levels of endogenous ETV1 expression that, when coupled with an activating KIT mutation, drives an oncogenic ETS transcription program. This differs from other ETS-dependent tumours such as prostate cancer, melanoma, and Ewing sarcoma where genomic translocation or amplification drives aberrant ETS expression9–11 and represents a novel mechanism of oncogenic transcription factor activation.

Changes in the Structure and Function of ICC Networks in ICC Hyperplasia and Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) express the receptor tyrosine kinase c-kit. Approximately 90% of GISTs have gain-of-function mutations in the Kit gene, which leads to its constitutive activation and drives malignant behavior of GISTs. Interstitial cells of Cajal (ICC) express c-kit; however, it is unknown whether uncontrolled hyperplasia of ICC is responsible for GISTs. Here, we sought to determine whether gain-of-function mutations in Kit lead to hyperplasia of all classes of ICC, whether ICC hyperplasia begins before birth, and whether functional defects occur in ICC hyperplasia or the development of GISTs. Heterozygous mutant Kit(V558Delta)/+ mice that develop symptoms of human familial GISTs and prematurely die from pathology of the gastrointestinal tract were utilized and compared with wild-type controls. C-kit-immunohistochemistry and intracellular electrical recording of spontaneous and nerve-evoked activity were applied to examine the density and functionality of ICC in these mutants. There was considerable hyperplasia in all classes of ICC throughout the GI tract of Kit(V558Delta)/+ mice, except for ICC in the deep muscular plexus of the intestine. Spontaneous electrical activity and postjunctional neural responses in hyperplastic ICC tissues appeared normal but were up-regulated in the cecum, where GISTs were commonly found. Kit gain-of-function leads to hyperplasia of most classes of ICC throughout the GI tract. ICC retain normal pacemaker function and enteric neural responses well after development of hyperplasia.

Microscopic Gastrointestinal Stromal Tumors in Esophageal and Intestinal Surgical Resection Specimens

Microscopic gastrointestinal stromal tumors (GISTs) (synonyms: sporadic interstitial cell of Cajal hyperplasia, seedling GISTs, minimal GISTs) are common incidental findings in gastroesophageal resections (9% to 35%). To our knowledge, their frequency, clinicopathologic features, and molecular pathogenesis from nongastroesophageal sites have so far not been sufficiently analyzed. We studied 19 lesions from distal esophagus (n=8), gastroesophageal junction (n=2), sigmoid colon (n=5), and vermiform appendix, cecum, rectum, and small intestine (1 each). Microscopic GISTs were detected in 0.2%, 0.1%, and 0.01% of routinely processed resection specimens from sigmoid colon, vermiform appendix, and rectum, respectively. Patients were 11 men and 8 women with a mean age of 66 years (range, 57 to 86 y). Thirteen patients had GI cancers and 5 had diverticular disease. None has a family history of GIST or features of neurofibromatosis 1. Lesions were 0.5 to 4 mm in size (mean, 1.12 mm), were all spindled and had noncircumscribed infiltrating borders. All arose in the muscularis propria and 2 were predominantly subserosal. Immunohistochemistry revealed a CD117/CD34/smooth muscle actin-negative phenotype in 18/19 lesions. Three KIT exon 11 mutations (2 point mutations and 1 deletion, all involving W557) were detected in 3/12 lesions with successful molecular analysis. In conclusion, incidental microscopic GISTs are uncommon in intestinal resections (< or =0.1%), contrasting with their gastroesophageal counterparts (> or =9%). Somatic KIT mutations are early initiating molecular events in a subset of them. The remarkable variation in the incidence of microscopic GISTs at different GI sites suggests an origin from heterogeneous subsets of interstitial cells of Cajal with varying potentials for neoplastic transformation.

A mouse model of a human multiple GIST family with KIT‐Asp820Tyr mutation generated by a knock‐in strategy

Several families exhibiting multiple gastrointestinal stromal tumours (GISTs) and germline c-kit gene mutations at exons 8, 11, 13, or 17 have been reported. These patients also exhibit diffuse hyperplasia of the interstitial cells of Cajal (ICCs) as a pre-existing lesion of multiple GISTs. We generated a mouse model of a family with germline c-kit gene mutation at exon 17, and compared the phenotypes between the mice and humans. The mouse counterpart (KIT-Asp818Tyr) of the human KIT-Asp820Tyr mutation was transmitted into germline by a knock-in strategy. Mating of male and female heterozygotes (KIT-Asp818Tyr/+) resulted in the generation of homozygotes (KIT-Asp818Tyr/KIT-Asp818Tyr). Histological examination revealed that all heterozygotes had both a small KIT-positive mesenchymal tumour at the caecum, consistent with GIST, and KIT-positive diffuse spindle-shaped cell proliferation in the distal oesophagus, stomach, proximal duodenum, and colon consistent with ICC hyperplasia. All homozygotes exhibited a larger caecal tumour and more prominent spindle-shaped cell proliferation compared with the heterozygous mice, and they usually died within 10 weeks after birth, likely due to ileus. The small intestine of both genotypes showed no apparent morphological abnormality, and autonomous contraction of the ileal segments appeared normal. Western blotting demonstrated that the caecal tumours expressed phosphorylated KIT, MAPK, Stat1, and Stat5. These mutant mice are considered to be useful for further investigation of the mechanism of GIST development as a result of ICC hyperplasia and for assessment of the in vivo effects of drugs against molecular targets.

Coexistence of interstitial cell of Cajal hyperplasia and microcarcinoidosis in a mature cystic teratoma of the ovary

Coexistence of interstitial cell of Cajal hyperplasia and microcarcinoidosis in a mature cystic teratoma of the ovary

Gain-of-Function Mutations of Receptor Tyrosine Kinases in Gastrointestinal Stromal Tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in human gastrointestinal tract. We first found that most GISTs expressed KIT, a receptor tyrosine kinase encoded by protooncogene c-kit and that approximately 90% of the sporadic GISTs had somatic gain-of-function mutations of the c-kit gene. Since both GISTs and interstitial cells of Cajal (ICCs) were double-positive for KIT and CD34, GISTs were considered to originate from ICCs or their precursor cells. We also found that germline gain-of-function mutations of the c-kit gene resulted in familial and multiple GISTs with diffuse hyperplasia of ICCs as the preexisting lesion. Moreover, we found that about half of the sporadic GISTs without c-kit gene mutations had gain-of-function mutations of platelet-derived growth factor receptor alpha (PDGFRA) gene that encodes another receptor tyrosine kinase. Imatinib which is known to inhibit constitutively activated BCR-ABL tyrosine kinase in chronic myelogenous leukemia also inhibits constitutive activation of mutated KIT and PDGFRA, and is now being used for metastatic or unresectable GISTs as a molecular target drug. Mutational analyses of c-kit and PDGFRA genes are considered to be significant for prediction of effectiveness of imatinib and newly developed/developing other agents on GISTs. Some mouse models of familial and multiple GISTs have been genetically created, and may be useful for further investigation of GIST biology.

Pathology of gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GIST) are the most common mesenchymal tumors in the gastrointestinal tract. It was found that most GIST expressed KIT, a receptor tyrosine kinase encoded by protooncogene c-kit. In normal gastrointestinal wall, KIT is expressed by interstitial cells of Cajal (ICC), which are a pacemaker for autonomous gastrointestinal movement. Because both GIST and ICC are double-positive for KIT and CD34, and because familial and multiple GIST appear to develop from diffuse hyperplasia of ICC, GIST are considered to originate from ICC or their precursor cells. It was also found that approximately 90% of the sporadic GIST have somatic gain-of-function mutations of the c-kit gene, and that the patients with familial and multiple GIST have germline gain-of-function mutations of the c-kit gene. These facts strongly suggest that the c-kit gene mutations are a cause of GIST. Approximately half of the sporadic GIST without c-kit gene mutations were demonstrated to have gain-of-function mutations in platelet-derived growth factor receptor-alpha (PDGFRA) gene that encodes another receptor tyrosine kinase. Because KIT is immunohistochemically negative in a minority of GIST, especially in PDGFRA gene mutation-harboring GIST, mutational analyses of c-kit and PDGFRA genes may be required to diagnose such GIST definitely. Imatinib mesylate was developed as a selective tyrosine kinase inhibitor. It inhibits constitutive activation of mutated KIT and PDGFRA, and is now being used for KIT-positive metastatic or unresectable GIST as a molecular target drug. Confirmation of KIT expression by immunohistochemistry is necessary for application of the drug. The effect of imatinib mesylate is different in various types of c-kit and PDGFRA gene mutations, and the secondary resistance against imatinib mesylate is often acquired by the second mutation of the identical genes. Mutational analyses of c-kit and PDGFRA genes are also significant for prediction of effectiveness of drugs including newly developed agents.

Gastrointestinal Stromal Tumors

Familial gastrointestinal stromal tumor (GIST) is a rare autosomal dominant genetic disorder. We report the second family to date with a germline point mutation in exon 17 of the KIT gene that leads to substitution of aspartic acid at position 820 with tyrosine (D820Y). One or more GISTs was documented in three generations of this kindred, and there was associated hyperplasia of the interstitial cells of Cajal (ICC). One affected family member complained of dysphagia and another suffered small intestinal diverticulosis with perforation, which may represent additional consequences of ICC hyperplasia. Diffuse and nodular ICC hyperplasia associated with the latter family member's small intestinal diverticulosis is illustrated, providing supportive functional and morphologic evidence for the ICC being the cell of origin of GISTs. Skin hyperpigmentation was not observed. Analysis of a 17-cm malignant GIST in the index patient revealed that it was hemi/homozygous for the germline D820Y mutation, indicating loss of the remaining wild-type KIT allele with tumor progression. Two smaller lesions from this patient were heterozygous for the mutation. This phenomenon has been observed in up to 8% of sporadic malignant GISTs but has not been documented in familial disease.

Sporadic Cajal cell hyperplasia is common in resection specimens for distal oesophageal carcinoma

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.

A Knock-In Mouse Model of Gastrointestinal Stromal Tumor Harboring Kit K641E

A mouse model of gastrointestinal stromal tumor (GIST) has been developed by a knock-in gene targeting strategy, which introduced a Kit gene K641E mutation, originally identified in sporadic human GISTs and in the germ line of familial GIST syndrome patients. Homozygous and heterozygous Kit K641E mice develop gastrointestinal pathology with complete penetrance and all Kit K641E homozygotes die by age 30 weeks due to gastrointestinal obstruction by hyperplastic interstitial cells of Cajal (ICC) or GISTs. Heterozygous mice have less extensive ICC hyperplasia and smaller GISTs, suggesting a dose-response relationship between oncogenically activated Kit and ICC proliferation. Immunoprecipitation and Western blotting reveal GISTs to contain abundant phosphorylated/activated Kit. In addition to ICC hyperplasia and GISTs, homozygous Kit K641E mice exhibit loss-of-function Kit phenotypes, including white coat color, decreased numbers of dermal mast cells, and sterility, indicating that despite its oncogenic activity the mutant form cannot accomplish many activities of the wild-type gene. Kit K641E reproduces the pathology associated with the familial GIST syndrome and thus is an excellent model to study Kit pathway activation, ICC biology, GIST pathogenesis, and preclinical validations of GIST therapies and mechanisms of drug resistance.

Gastrointestinal stromal tumors: their origin and cause.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the gastrointestinal tract. Recently, we found that GISTs expressed KIT, a receptor tyrosine kinase encoded by the protooncogene c-kit. We propose that GISTs may originate from interstitial cells of Cajal (ICCs), which are considered to be pacemaker cells for the autonomous movement of the gastrointestinal tract. There are major two reasons for this proposal: one is that both GISTs and ICCs are double-positive for KIT and CD34, and the other is that multiple GISTs appear to develop from diffuse ICC hyperplasia in germline mutations of the c-kit gene. Because somatic gain-of-function mutations of the c-kit gene are observed in solitary GISTs, and because the germline gain-of-function mutations of the c-kit gene are observed in familial and multiple GISTs, the gain-of function mutations of the c-kit gene are considered to be a cause of the development of GISTs.