Strong PDGFRA positivity is seen in GISTs but not in other intra-abdominal mesenchymal tumors: Immunohistochemical and mutational analyses.

Mutation of the platelet-derived growth factor receptor-alpha (PDGFRA) gene has been well documented as an alternative oncogenic mechanism in a subset of gastrointestinal stromal tumors (GISTs) lacking c-kit mutations. However, the role of PDGFRA immunohistochemistry in the diagnosis of GISTs has not been well studied. We investigated PDGFRA immunoreactivity in GISTs and in other intra-abdominal mesenchymal tumors, and correlated PDGFRA expression with CD117 positivity and with the mutational status of PDGFRA and c-kit genes. In addition, expression of phosphorylated AKT, an activated downstream molecule in the PDGFRA and c-kit signaling pathways, was correlated with PDGFRA and CD117 status. A total of 39 GISTs and 20 other mesenchymal tumors in the abdomen were included in this study. Thirty-five of 39 GIST cases (89.7%) were positive for PDGFRA and 19 of these 35 positive cases were strongly positive. Five of 20 non-GIST lesions (25%) were positive for PDGFRA, but none of these cases were strongly positive. With one exception, PDGFRA-positive cases were also positive for CD117. Phosphorylated AKT positivity was not associated with the immunoreactivity or mutation of PDGFRA and c-kit, suggesting that the activation of AKT is probably independent of the activation of PDGFRA and c-kit in GISTs. Of 14 GISTs assayed, 4 had mutations in c-kit at exons 11 or 17, and 4 had mutations in PDGFRA at exons 12 or 18. Three of 4 GIST cases with PDGFRA mutations show epithelioid morphology and strong PDGFRA immunoreactivity with prominent perinuclear dotlike accentuation (so-called Golgi pattern). In conclusion, strong PDGFRA positivity with Golgi pattern is a useful adjunct in the diagnosis of GISTs with PDGFRA mutation.     

High-resolution melting amplicon analysis as a method to detect c-kit and platelet-derived growth factor receptor alpha activating mutations in gastrointestinal stromal tumors

High-resolution melting amplicon analysis (HRMAA) was used to detect c-kit and platelet-derived growth factor receptor alpha (PDGFRA) activating mutations in 96 gastrointestinal stromal tumors (GISTs). HRMAA detected mutations in 87 GISTs (91%). Of the 87 cases, 69 (79%) contained c-kit mutations and 18 (21%), PDGFRA mutations. One c-kit mutation-positive case contained an exon 9 mutation, ins FY at codon 503, that has not been previously described. One PDGFRA mutation-positive case contained mutation D842V del 843, also not previously described. Of 18 PDGFRA mutation-positive cases, 3 (17%) were strongly positive for kit expression as measured by CD117 immunohistochemical analysis. Of 69 c-kit mutation-positive cases, 66 (96%) showed strong kit immunohistochemical expression, but 3 (4%) showed negative to weak CD117 expression. Of 96 cases, 9 (9%) were wild type for c-kit and PDGFRA. Of the wild-type cases, 8 still showed strong immunohistochemical kit expression, whereas 1 showed weak kit expression. GISTs with PDGFRA mutations were found in the stomach, omentum, and peritoneum but not the small intestine. GISTs with c-kit exon 9 mutations were found primarily in the small intestine. HRMAA is a sensitive technique that can be used to rapidly identify c-kit and PDGFRA activating mutations in GISTs.     

CD117阴性的胃肠道间质瘤的超微结构特点及基因突变检测

目的探讨CD117阴性的胃肠道间质瘤（GIST）的超微结构及c-kit和血小板源性生长因子受体A（PDGFRA）基因的突变情况。方法用免疫组织化学方法（EnVision法和SP法）从101例GIST中筛选到6例CD117阴性的GIST,观察了6例CD117阴性的胃肠道间质瘤的电镜变化,用PCR直接测序的方法检测6例CD117阴性的胃肠道间质瘤的c-kit基因外显子9、11、13、17和PDGFRA基因外显子12和18突变。结果电镜下观察到6例GIST的超微结构特点与卡哈尔细胞相似,通过PCR直接测序检测揭示c-kit基因9、11、13和17外显子均无突变,而3例GIST的PDGFRA有突变,其中2例D842V突变,1例R841S突变。结论PDGFRA基因的突变可能是CD117阴性的胃肠道间质瘤发生的重要分子基础。     

165例胃肠道间质瘤中c-kit和PDGFRA基因突变的检测和临床诊断意义

目的探讨在中国较大样本的胃肠道问质瘤（GIST）中c-kit基因和PDGFRA基因的突变状况,为进一步的生物靶向治疗提供依据。方法用免疫组织化学EnVision法、聚合酶链反应（PCR）扩增和直接测序的方法,检测165例GIST c-kit基因9、11、13和17号外显子突变以及PDGFRA基因12和18号外显子突变。结果病理组织学诊断的165例GIST病例中有155例（94％）免疫组织化学显示CD117阳性。在CD117阳性的GIST中,c-kit基因总突变率为76．1％（118／155）：分别为11号外显子67．1％（104／155）、9号外显子7．1％（11／155）、13号外显子1．3％（2／155）和17号外显子0．6％（1／155）。绝大多数为杂合性突变,少数为纯合性突变。11号外显子的突变位点多集中在5’端的经典热点,其次为3’端的框内串联重复。后者主要以核分裂象少的老年女性胃部病例多见。9号外显子突变代表一类发生在年轻男性体积较大的小肠病变。13号外显子发现一处新的突变点L641P。PDGFRA基因突变见于50％（5／10）CD117阴性病例,均为18号外显子突变,包括常见的D842V点突变和一个框内843-846处IMHD缺失伴有S847T的新突变。PDGFRA基因突变多见于发生在后腹膜／网膜的具有高度侵袭危险性的病例。结论中国GIST病例大多数存在c-kit基因和PDGFRA基因的突变,且在基因突变类型和肿瘤原发部位问有非随机的联系。除了发现几个新的突变形式外,国人的GIST似乎和西方国家有些不同的突变特点。靶向治疗需要基因突变分型的启示和指导。     

Multiple gastrointestinal stromal tumors with a germline c-kit mutation

Familial gastrointestinal stromal tumor (GIST) is a rare autosomal dominant genetic disorder; thus far, only seven families have been reported with c-kit germline mutations. Presented herein is a case of multiple intestinal GIST in a 38-year-old man with a germline mutation of the c-kit gene. Operative specimens of the jejunal segment and multiple wedge resection specimens included approximately 30 masses, ranging in size from 1.0 to 6.0 cm. Microscopically, the tumors were composed of CD117-positive spindle/epitheloid cells with variable numbers of mitotic counts, a characteristic of GIST. The mitotic rate increased to more than 5/50 high-power fields. Interestingly, marked hypertrophy of the myenteric plexus with CD117-positive cells was identified in the intestinal segment. By polymerase chain reaction-single-strand conformation polymorphism analysis and direct DNA sequencing, a heterozygous c-kit missense mutation at nucleotide 1676 of codon 559 (T --> C, Val --> Ala), part of the juxtamembrane domain, was detected in the normal tissue. The same mutation was homozygous in the tumor samples. The present case is the first proven case of multiple GIST with a c-kit germline mutation in Korea and is distinguishable from other reported germ-line c-kit mutations because the same 1676 T --> C missense mutation occurs in the normal allele as well as the affected allele, although the significance of the identical mutations remains to be investigated.     

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.     

Mutations in Exon 11 of c-Kit Occur Preferentially in Malignant versus Benign Gastrointestinal Stromal Tumors and Do Not Occur in Leiomyomas or Leiomyosarcomas

Gastrointestinal stromal tumors (GISTs) comprise the largest subset of mesenchymal tumors of the gastrointestinal tract. These neoplasms differ histologically and immunohistochemically from typical leiomyomas and leiomyosarcomas. Most GISTs express CD34 and CD117 (c-kit protein) but not desmin. Recently, gain-of-function mutations of c-kit proto-oncogene have been shown in five solitary GISTs and in tumors and leukocytes from a family with multiple GISTs. An in-frame deletion or a point mutation in exon 11 of c-kit was detected in these cases. Stable transfection of the mutant c-kit complementary DNA was also shown to induce malignant transformation of murine lymphoid cells, suggesting that the c-kit mutations contribute to tumor development. In this study, we evaluated 43 GISTs and 14 smooth muscle tumors for mutations in the exon 11 of c-kit by a PCR-assay. Half of the malignant GISTs (12/24) and only one benign GIST (1/19) revealed mutant bands. No mutant bands were found in 3 leiomyomas and 11 leiomyosarcomas. Sequence analysis confirmed the presence of an in-frame deletion of 3–21 bp in all 13 GISTs with mutant bands. Wild-type bands from 8 malignant and 11 benign GISTs and 7 smooth muscle tumors without mutant bands were cloned and sequenced. Additional mutations were found in 3 malignant and 2 benign GISTs. There were no mutations in 3 leiomyomas and 4 leiomyosarcomas. The mutation status of exon 11 did not correlate with immunohistochemically detectable expression of the CD117, as virtually all GISTs with or without such mutations showed CD117 immunoreactivity. The c-kit mutations occur preferentially in malignant GISTs and might be a clinically useful adjunct marker in the evaluation of GISTs. The conservation of the c-kit mutation pattern, observed in consecutive lesions from the same patients, suggests that these mutations might be useful tumor markers in monitoring recurrence or minimal residual disease.     

Use of tissue microarrays and immunohistochemistry to standardize the diagnosis of gastrointestinal stromal tumors

We assessed the concordance among seven general pathologists with respect to histologic diagnosis and interpretation of c-kit proto-oncogene (KIT) and platelet-derived growth factor receptor alpha (PDGFRA) immunostaining of 36 cases of primary spindle-cell tumor, predominantly of the gastrointestinal tract, mesentery, and retroperitoneum, based on review of a tissue microarray (TMA) subjected to immunohistochemistry with antibodies to KIT/CD117, PDGFRA, vimentin, desmin, smooth muscle action, CD34, and S-100 protein. Tumors included 20 molecularly analyzed gastrointestinal stromal tumors (GISTs), 4 leiomyosarcomas, 4 schwannomas, 4 desmoid-type fibromatoses, and 4 solitary fibrous tumors. The mean overall concordance with original diagnosis for each histologic type was 91.1%, with a mean kappa value of 0.91. With respect to PDGFRA immunostaining, the four GISTs with PDGFRA mutation were interpreted as cytoplasm positive, but the 16 GISTs with c-kit mutation were interpreted as weak or positive. These results indicate that the overall concordance with original diagnosis in mesenchymal tumors with the use of immunohistochemical panels is high, despite the use of TMAs. To some extent, PDGFRA immunophenotyping may be useful in GISTs with PDGFRA mutation, but it was not highly reproducible or specific. Therefore, in KIT-negative or weakly positive GISTs, mutation analysis will be required.     

Dual CD117 expression in gastrointestinal stromal tumor (GIST) and paraganglioma of Carney triad: a case report

Carney triad is a rare syndrome, with only 20 complete cases reported. We report a 36-year-old white woman with complete Carney triad, including metastatic gastric stromal tumor (GIST), pulmonary chondroma, and nonfunctioning extra-adrenal paraganglioma. Immunohistochemistry was positive for CD34 and CD117 (c-kit) in the GIST, and positive for chromogranin and CD117 in the paraganglioma. Ultrastructural studies demonstrated skeinoid fibers in the GIST. To our knowledge, this is the 21st complete Carney triad case reported and the first report of dual expression CD117 in both GIST and paraganglioma, a finding with intriguing pathogenetic implications related to the organization of the autonomic nervous system.     

Immunohistopathological and molecular genetic features of a case in which gastrointestinal stromal tumor recurred five times

Gastrointestinal stromal tumor (GIST) is a distinct group of mesenchymal neoplasms recently shown to exhibit differentiation toward interstitial cells of Cajal. Although previous studies have shown that the clinical outcome of patients with GIST is associated with mitotic activity, the proliferation index determined by the Ki-67 labeling index, immunophenotype (CD34 and/or p53) and mutation in exon 11 of the c-kit, a definitive discrimination between benign and malignant GIST has not yet been established. We report a patient in whom malignant GIST in the abdomen recurred five times. In this case, the primary GIST and the five recurrent GIST were associated with c-kit immunoreactivity, but the mitotic index of the GIST tended to be increasingly higher with subsequent recurrences. Mutational analysis of the c-kit revealed that the primary and recurrent GIST were mutant-negative. These data indicated that 'morphologically appearing benign' tumors with lower proliferative parameters may also have the capacity of metastasis and recurrence.     

Histopathological and cytological findings in a case of gastrointestinal stromal tumor presenting in the pelvic cavity

Gastrointestinal stromal tumor (GIST) usually occurs in the gastrointestinal tract, mainly in the stomach. Recently, GIST arising in extragastrointestinal organs was been reported. This case was a 49-year-old female who was diagnosed as having uterine leiomyoma and pelvic tumor in the rectovaginal septum. The pelvic tumor showed no connection with the uterus and rectum. Grossly, the pelvic tumor was light brown and solid. Cytologically, the tumor cells of the pelvic tumor showed vague interlacing fascicles with spindle/fibrous cytoplasm and elongated nuclei. No necrosis or mitosis was present. Histological findings of the pelvic tumor revealed an interlacing bundle fashioned with one to two mitotic figures per 50 HPE No necrosis was found in the tumor. The tumor cells were positive for CD117 (c-kit protein), CD34, and vimentin by immunohistochemistry, but negative for actin, desmin, and S-100. The tumor was diagnosed as GIST in the pelvic cavity. GIST rarely presents in extragastrointestinal regions such as this case. It is difficult to make a differential diagnosis between GIST and other mesenchymal spindle cell tumors only from a cytologic specimen. A positive reaction for CD117 is useful for the diagnosis of GIST.     

Primary gastrointestinal stromal tumor of the esophagus in an HIV-positive patient

We describe a rare case of malignant gastrointestinal stromal tumor (GIST) of the esophagus presenting in an HIV-positive man. Not only did the tumor arise from an unusual anatomic site for GIST, namely, the esophagus, but it also had a predominant epithelioid cell morphology that is uncommon and preferentially associated with aggressive behavior. Exhaustive immunohistochemical studies showed strong reactivities to the classic GIST marker, CD34, and to the current more sensitive and more specific GIST marker, CD117/ c-kit protein. This immunophenotype corresponded to that of stromal tumors arising in the more common sites like stomach and small intestine as well as to that of a reported series of esophageal GISTs in the general population. Mutations of the c-kit protein was detected in the tumor, confirming previous observations. This further documents that esophageal GIST and the more common benign esophageal spindle cell lesions are pathologically distinct entities and despite its rarity, esophageal GIST should be recognized by pathologists and clinicians. The occurrence of this tumor in an HIV-positive patient is coincidental, and it resulted in an extremely unusual metastatic site that has not been reported for GISTs.     

Gastrointestinal stromal tumours--an update for histopathologists

This review aims to summarize recent knowledge gained about gastrointestinal stromal tumour (GIST) of particular relevance to histopathologists. KIT and PDGFRA mutation analyses can be useful for confirming a diagnosis of GIST, but there are some diagnostic limitations to these analyses, and so immunohistochemical markers currently remain crucial to the diagnostic process. Of these markers, CD117 and Discovered on GIST 1 (DOG1) are currently the most sensitive and specific markers of GIST, and recent data appear to disprove the fear that antigen retrieval causes false-positive CD117 immunostaining. The accurate prognostication of GIST has been greatly helped by the National Institutes of Health (NIH) and Armed Forces Institute of Pathology (AFIP) classification systems, although both systems still have limitations, and the behaviours of certain GIST subgroups are less well predicted by both systems. KIT and PDGFRA mutation analyses can help to predict the response of GISTs to receptor tyrosine kinase inhibitors, and both GISTs that respond and those that show resistance to these inhibitors may show characteristic pathological changes. Some GIST subgroups (e.g. Carney syndrome and paediatric GISTs) have had recently described clinicopathological and/or molecular characteristics which may help with the diagnosis and/or treatment of these specific neoplasms.     

Molecular analysis of c-Kit and PDGFRA in GISTs diagnosed by EUS

Gastrointestinal stromal tumors (GISTs) are characterized by overexpression and mutations of c-Kit. Approximately 80% of c-Kit mutations occur in exon 11, being a response factor to imatinib (Gleevec) therapy. Mutations of platelet-derived growth factor receptor-alpha (PDGFRA) are observed in a subset of GISTs lacking c-Kit mutations.We aimed to assess whether c-Kit and PDGFRA mutation analysis of GISTs obtained by endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) could be routinely performed. Mutation analysis of c-Kit hotspot exons (9, 11, 13 and 17) and PDGFRA hotspot exons (12 and 18) was performed in aspirates of 33 GISTs and 18 non-GIST mesenchymal tumors.Of the GIST cases, 19 (58%) of 33 contained a mutation in exon 11, 1 (3%) in exon 9, and none in exons 13 and 17. No activating c-Kit mutations were identified in non-GIST cases. No PDGFRA mutation was detected.Mutation analysis is possible in these FNA cell blocks and can assist in the diagnosis and therapeutic decisions in GIST cases/     

Synchronous poorly-differentiated neuroendocrine carcinoma and gastrointestinal stromal tumor of the stomach: a case report with immunohistochemical and molecular genetic analyses of KIT and PDGFRA

Although the stomach is the most common location for gastrointestinal stromal tumor (GIST) with co-primary tumors, the synchronous appearance of a poorly differentiated neuroendocrine carcinoma (NEC) and GIST in the stomach is extremely rare. To the best of our knowledge, this is the first case of gastric GIST coexisting with gastric NEC to be reported in the literature. The current study reports the case of a 71-year-old male with gastric poorly differentiated NEC and GIST discovered incidentally during surgical treatment of the NEC. Immunohistochemistry analysis showed that the NEC tumor cells were positive for CK (cytokeratin), CD57, synaptophysin, chromogranin, CD117 (KIT protein), Dog-1 (discovered on GIST-1 protein) and CD34. The synchronous GIST immunophenotype showed positivity for CD117, Dog-1 and CD34 (100%), whereas staining for CK, SMA, desmin and S100 was negative. Ki-67 labeling of proliferating cells was 90% in NEC and 1% in GIST. An accurate diagnosis was confirmed by immunohistochemical findings. Furthermore, genetic analysis using PCR direct sequencing identified no mutations in the KIT (exons 9, 11, 13 and 17) and PDGFRA (exons 12 and 18) genes. The patient developed lymph node metastases and underwent cisplatin-based chemotherapy after the operation. This is the first documented case of synchronous gastric GIST and NEC with the examination of protein expression and gene mutations in KIT and PDGFRA, which will help to further understand the etiology and pathogenesis of NEC coexisting with GIST in a gastric location.     

Gastro-intestinal stromal tumour--role of CD117 in diagnosis and management

Gastro-intestinal stromal tumours (GIST) are a biologically distinct heterogenous group of tumours of the gut. They are said to arise from interstitial cells of Cajal in gut wall. The turnour results from mutation of c-kit gene which codes for CD117 containing tyrosine kinase receptor of Cajal cells. Identification of this mutation by immunohistochemistry (IHC) is the key to the diagnosis of these tumours. CD117 negative GISTs develop from gene mutation through alternate pathway (PDGFRA). The accurate diagnosis is important as specific chemotherapeutic agents are now available for their management. We have studied 8 cases of GISTs during last 2 years in our institute. Half of the cases were female, six cases were in the age group between 35 to 50 years, the other two being of 19 and 70 years. On histology, 5 cases were categorized as high grade on the basis of their size and mitotic count. All cases were subjected to IHC. Only 4 cases were CDll7 positive, one case was positive for S100 and one case for SMA. Remaining 2 cases, negative for CD117, S100 and SMA, histologically resembled GISTs. CD117 positive cases are ideal candidates for treatment with molecularly targeted specific chemotherapeutic agents, e.g., imatinib as these tumours are non-responsive to conventional chemotherapy. Histologically diagnosed stromal tumours of the gut should be subjected to immunostain for CD117 so that specific medical management can be provided to prevent recurrence and metastasis as well as pre-operative debulking of the tumour.     

CD117阴性胃肠道间质瘤的临床病理及免疫组织化学研究

目的 探讨免疫组织化学在形态学典型、免疫组织化学CD117阴性胃肠道间质瘤(GIST)诊断中的意义.方法 对10例CD117阴性、形态学典型的GIST进行c-kit基因第9、11、13、17号外显子及血小板源性生长因子受体α(PDGFRA)基因第12和18号外显子的基因检测,同时所有病例均进行CD117、CD34、平滑肌肌动蛋白(SMA)、结蛋白、S-100蛋白、WT-1、DOG-1 的免疫组织化学染色(EnVision法).结果 10例中8例完成c-kit及PDGFRA基因的检测,仅1例有c-kit基因第9号外显子突变,余未发现基因突变.10例CD117阴性的病例9例CD34阳性,2例SMA局灶阳性.结蛋白和S-100蛋白均阴性.DOG1弥漫阳性者5例,1例弥漫弱阳性,2例局灶阳性,2例阴性.4例WT-1弥漫阳性,2例局灶阳性,1例有散在肿瘤细胞阳性,3例阴性.结论 对胃肠道及胃肠道外形态学典型、但CD117阴性的GIST病例,联合应用多种免疫组织化学标记有助于诊断.DOG-1和WT-1可作为补充加入到CD117阴性GIST的诊断中.     

Anal spindle cell lesion

Anal lumps are often clinically diagnosed as thrombosed or torted haemorrhoids or polyps. We report the case of an elderly woman who presented with a polypoid anal lesion, which showed pleomorphic spindle cell morphology on microscopy. Immunohistochemical stains revealed this to be a melanoma, which diffusely and strongly expressed CD117/c-kit protein. There is potential for misdiagnosis of CD117-positive amelanotic anal melanoma as a gastrointestinal stromal tumour (GIST), if a panel of immunohistochemistry markers is not performed. Melanoma comprises 0.25–1.25% of all anorectal malignancies. They are highly aggressive tumours, being unresponsive to both radical and local control with a poor 5-year survival of 10–15%. Previous studies have reported CD117 positivity in a small number of anorectal melanomas, a minority of which have shown c-kit mutation similar to those in GISTs. Melanomas are resistant to conventional chemotherapy and radiation and the presence of a c-kit mutation may offer a possible new alternative via gene-targeted therapy using the c-kit inhibitor imatinib Glivec. Accordingly we reviewed the literature and submitted the tumour for KIT mutational analysis.     

c-kit gene mutation and CD117 expression in human anorectal melanomas

c-kit and BRAF mutations play an important role during the pathogenesis of melanoma. The subtypes of melanomas arising from different parts of the body have variable c-kit or BRAF mutation frequencies. Few studies in the literature have examined c-kit and BRAF mutation status in melanomas that occur in the anus and rectum. In this study, we analyzed 40 cases of anorectal melanoma for c-kit and BRAF mutations by DNA sequencing using paraffin-embedded tissues. c-kit Mutations were detected in exons 9, 11, 13, and 17. CD117 expression in tumor cells was analyzed by immunohistochemistry. Our study showed that a c-kit mutation was found in 7 of the 40 cases of anorectal melanoma. CD117 expression was detected in 16 of the 40 cases, and 3 of these 16 cases also had c-kit mutations. Mutations in BRAF were also identified in 2 patients. These results indicate that a subset of anorectal melanomas have activating c-kit mutations, which suggests that kinase inhibitors such as imatinib may be used to treat this subset of melanoma patients. In addition, our results show that c-kit mutations do not correlate with CD117 expression.     

CD117阴性胃肠道间质瘤的临床病理及免疫组织化学研究

目的 探讨免疫组织化学在形态学典型、免疫组织化学CD117阴性胃肠道间质瘤(GIST)诊断中的意义.方法 对10例CD117阴性、形态学典型的GIST进行c-kit基因第9、11、13、17号外显子及血小板源性生长因子受体α(PDGFRA)基因第12和18号外显子的基因检测,同时所有病例均进行CD117、CD34、平滑肌肌动蛋白(SMA)、结蛋白、S-100蛋白、WT-1、DOG-1 的免疫组织化学染色(EnVision法).结果 10例中8例完成c-kit及PDGFRA基因的检测,仅1例有c-kit基因第9号外显子突变,余未发现基因突变.10例CD117阴性的病例9例CD34阳性,2例SMA局灶阳性.结蛋白和S-100蛋白均阴性.DOG1弥漫阳性者5例,1例弥漫弱阳性,2例局灶阳性,2例阴性.4例WT-1弥漫阳性,2例局灶阳性,1例有散在肿瘤细胞阳性,3例阴性.结论 对胃肠道及胃肠道外形态学典型、但CD117阴性的GIST病例,联合应用多种免疫组织化学标记有助于诊断.DOG-1和WT-1可作为补充加入到CD117阴性GIST的诊断中.

Abstract：

Objective To study the immunophenotype and c-kit or platelet derived growth factor receptor alpha(PDGFRA)gene mutations in CD117-negative gastrointestinal stromal tumors(GISTs).Methods Ten cases of GISTs with typical histologic features but no CD117 expression were retrieved from the archival of Department of Pathology,Peking Union Medical College Hospital,China.The Cages were further evaluated for the presence of c-kit exons 9.11, 13 and 17 mutations and PDGFRA exons 12 and 18mutations.DNA was extracted from the paraffin-embedded tuinor tissue.The PCR products were sequenced directly for the mutations.An immunohistochemical study for CD117,CD34,smooth muscle actin,desmin,S-100 protein.WT-1 and DOC-1 Was also performed.Results Eight of the 10 Cases had the mutation tests completed.C-kit mumfion in exon 9 Wag detected in only one case.Amongst the 10 cases studied, CD34Wag expressed in 9 cases. Smooth muscle actin was focally positive in 2 cases.None of them expressed desmin or S-100 protein.DOG-1 and WT-1 were diffusely positive in 5 and 4 Cages.respectively.In addition.DOG1 Was diffusely but weakly positive in 1 case and focally expressed in 2 cages.Three cases were focally positive for WT-1.Conclusion Pathologic diagnosis of CD117-negative GISTs can be facilitated with the application of a panel of immunohistochemical markers.including DOG-1 and WT-1.