New Mechanisms of mTOR Pathway Activation in KIT-mutant Malignant GISTs.

A great majority of gastrointestinal stromal tumors (GISTs) are primarily driven by gain-of-function KIT receptor tyrosine kinase mutations that subsequently lead to activation of phosphatidiylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway, a downstream effector of KIT signaling. KIT tyrosine kinase inhibitor, imatinib mesylate, has been successfully used for the treatment of primary, advanced, and disseminated GISTs. Recently, activation of mTOR pathway independent of KIT signaling was demonstrated in imatinib mesylate naïve malignant GISTs and treatment-resistant metastatic tumors. This activation was attributed to oncogenic mutations in PIK3CA encoding PI3K 110α subunit, or to the inactivation of PTEN tumor suppressor, a potent mTOR negative regulator. In this study, mTOR pathway genes were evaluated in 14 imatinib mesylate naïve, KIT-mutant, malignant small intestinal GISTs using next-generation sequencing. Mutations were detected in 3 (21%) of 14 analyzed tumors: (1) c.3200A>T substitution in PIK3CB encoding PI3K 110ß subunit, (2) c.1040A>G substitution in tuberous sclerosis complex (TSC2) encoding tuberin, mTOR down-regulator (3) c.6625C>G substitution in mTOR. At the protein level, these changes were predicted to cause, respectively, PIK3CB p.D1067V, TSC2 p.K347R, and mTOR p.L2209V mutations. Previously reported "in vitro" experiments with mouse 3T3 fibroblasts demonstrated oncogenic potential of PIK3CB p.D1067V and mTOR p.L2209V mutants; whereas, PolyPhen-2 software analysis predicted TSC2 p.K347R mutation to likely have a damaging impact on tuberin function. The results of this and previous studies indicate diversity of genetic changes leading to activation of PI3K-AKT-TSC-mTOR pathway in malignant GISTs. Extensive genotyping of the genes involved in mTOR pathway demonstrates common alterations that need to be considered in targeted treatment.

SP174 Antibody Lacks Specificity for NRAS Q61R and Cross-Reacts With HRAS and KRAS Q61R Mutant Proteins in Malignant Melanoma.

HRAS, KRAS, and NRAS, highly homologous proteins, are often mutationally activated in cancer. Usually, mutations cluster in codons 12, 13, and 61 and are detected by molecular genetic testing of tumor DNA. Recently, immunohistochemistry with SP174 antibody has been introduced to detect NRAS Q61R-mutant protein. Studies on malignant melanomas showed that such an approach could be a viable alternative to molecular genetic testing. This investigation was undertaken to evaluate the value of SP174 immunohistochemistry for detection of NRAS Q61R-mutant isoform. Two hundred ninety-two malignant melanomas were evaluated using Leica Bond-Max automated immunostainer. Twenty-nine tumors (10%) showed positive immunoreactivity. NRAS codon 61 was polymerase chain reaction amplified and sequenced in 24 positive and 92 negative cases using Sanger sequencing, quantitative polymerase chain reaction, and next-generation sequencing approaches. A c.182A>G substitution leading to NRAS Q61R mutation was identified in 22 tumors. Two NRAS wild-type tumors revealed c.182A>G substitutions in HRAS and KRAS codon 61, respectively. Both mutations were detected by next-generation sequencing and independently confirmed by Sanger sequencing. None of 85 NRAS codon 61 wild-type tumors and 7 NRAS mutants other than Q61R showed immunoreactivity with SP174 antibody. Thus, SP174 antibody was 100% sensitive in detecting NRAS Q61R-mutant isoform in malignant melanoma, but not fully specific as it cross-reacted with HRAS and KRAS Q61R-mutant proteins. Therefore, molecular testing is needed to determine which RAS gene is mutated. The rarity of HRAS and KRAS Q61R mutants in malignant melanoma let previous investigations erroneously conclude that SP174 is specific for NRAS Q61R-mutant protein.

SP174, NRAS Q61R Mutant-Specific Antibody, Cross-Reacts With KRAS Q61R Mutant Protein in Colorectal Carcinoma.

CONTEXT: - NRAS is a member of the RAS family oncoproteins implicated in cancer. Gain-of-function NRAS mutations were reported in a subset of colorectal cancers. These mutations occur at codons 12, 13, and 61 and are detected by molecular genetic testing. Recently, an antibody (clone SP174) became available to immunohistochemically pinpoint NRAS Q61R mutant protein. In malignant melanoma, NRAS Q61R mutant-specific immunohistochemistry was shown to be a valuable supplement to traditional genetic testing. OBJECTIVE: - To evaluate the significance of NRAS Q61R mutant-specific immunohistochemistry in a cohort of colorectal carcinomas. DESIGN: - A total of 1185 colorectal carcinomas were immunohistochemically evaluated with SP174 antibody. NRAS Q61R mutant-specific immunohistochemistry was validated by molecular genetic testing including Sanger sequencing, quantitative polymerase chain reaction (qPCR), and next-generation sequencing. RESULTS: - Twelve tumors showed strong SP174 immunoreactivity. Sanger sequencing detected an identical c.182A>G substitution, causing NRAS Q61R mutation at the protein level, only in 8 SP174-positive cases. These results were confirmed by qPCR study. Subsequently, NRAS wild-type tumors with strong SP174 staining were evaluated by next-generation sequencing and revealed KRAS c.182A>G substitutions predicted to cause KRAS Q61R mutation. Review of colorectal carcinomas with known KRAS and NRAS genotype revealed that none of 62 wild-type tumors or 47 mutants other than Q61R were SP174 positive. CONCLUSION: - SP174 immunohistochemistry allows sensitive detection of NRAS and KRAS Q61R mutants. However, molecular genetic testing is necessary to determine specifically which RAS gene is mutated.

MAGE-A is More Highly Expressed Than NY-ESO-1 in a Systematic Immunohistochemical Analysis of 3668 Cases.

Two cancer testis antigens, the New York esophageal squamous cell carcinoma-1 (NY-ESO-1) and the melanoma-antigen family A (MAGE-A), represent promising immunotherapy targets due to the low expression of these antigens in nonmalignant tissue. To assess overexpression patterns in various cancers, we performed a systematic immunohistochemical analysis for NY-ESO-1 and MAGE-A on tissue array samples of 3668 common epithelial carcinomas (CA) and germ cell tumors of high prevalence and mortality. Here, we find significantly higher expression of MAGE-A (>50% on tumor cells) compared with NY-ESO-1 in several CAs including cutaneous squamous cell carcinomas (SCC) (52.8%/2.8%), esophageal SCC (50%/0%), head and neck SCC (41.1%/<1%), bladder urothelial CA (40.4%/8.3%), cervical/anal SCC (37.5%/0%), lung SCC (34%/3.8%), lung adenocarcinomas (27.6%/3.9%), ovarian CA (26.4%/3.6%), endometrial CA (26.3%/1.3%), lung small cell CA (24.4%/2.4%), gastric adenocarcinomas (20%/4%), breast mucinous CA (19.3%/0%), hepatocellular CA (18.8%/1.2%), breast infiltrating ductal CA (16.4%/1.8%), colorectal adenocarcinomas (10.7%/<1%), cholangiocarcinomas (9.8%/0%), thymic CA (9%/4.5%), and mesotheliomas (7.9%/<1%). Furthermore, high expression of MAGE-A, but not NY-ESO-1, was seen in whole slide evaluations of an independent cohort of metastatic SCC (45.5%/3.6%) and metastatic CA (13.5%/0%) of various primaries with significantly higher expression of MAGE-A in metastatic SCC compared with other metastatic CA. MAGE-A is also more highly expressed in germ cell tumors, seminomas (69%/3.5%) and nonseminomas (40.1%/4.7%). In summary, MAGE-A is more highly expressed than NY-ESO-1 in a majority of human malignancies, and targeting MAGE-A may benefit a large number of patients.

Frequency and clinicopathologic profile of PIK3CA mutant GISTs: molecular genetic study of 529 cases.

Gastrointestinal stromal tumors (GISTs) are mesenchymal tumors usually driven by the mutational activation of receptor tyrosine kinases, KIT, or PDGFRA. Oncogenic activation of phosphatidylinositide-3-kinase (PI3K), a downstream effector in the KIT signaling pathway, has been identified in different types of cancer, with the PI3K 110α subunit encoded by PIK3CA being a common mutational target. In this study, the mutational hotspot in the PIK3CA kinase domain encoded by exon 20 was evaluated in 529 imatinib-naive GISTs using PCR amplification and Sanger sequencing. Eight mutations (two co-existing in one tumor) were identified. Subsequently, The cobas PIK3CA Mutation Test was employed to evaluate mutational hotspots in exons 1, 4, 7, and 9 in 119 PIK3CA exon 20-wild type tumors. In two cases, mutations in exons 1 and 9 were identified. In one GIST, previously undetected by Sanger sequencing, the exon 20 mutation was discovered. Altogether, eight primary and two metastatic GISTs carried PIK3CA mutations. The size of primary PIK3CA-mutant GISTs was ≥14 cm (mean size 17 cm), and mitotic activity varied from 0 to 72 per 50HPF (mean 5/50HPF). Follow-up data showed short survival in 6 of 7 studied cases. Detection of PIK3CA mutations in large or metastatic KIT-mutant GISTs may suggest that PIK3CA-mutant clones have a proliferative advantage during disease progression. Tyrosine kinase inhibitors have been successfully used in GIST treatment. However, resistance frequently develops due to secondary KIT mutations or activation of downstream to KIT signaling pathways, such as the PI3K/AKT/mTOR pathway. PIK3CA mutations similar to the ones detected in GISTs have been shown to cause such activation. Therefore, genotyping of PIK3CA in GISTs might help to pinpoint primary and metastatic tumors with the potential to develop resistance to tyrosine kinase inhibitors and guide therapy with PI3K inhibitors.

Oncogenic Activation of the Wnt/ß-Catenin Signaling Pathway in Signet Ring Stromal Cell Tumor of the Ovary.

Signet ring stromal cell tumor (SRSCT) of the ovary is a very rare benign ovarian neoplasm. To date, no underlying genetic mechanism has been identified. In this study, 50 oncogenes and tumor suppressor genes were evaluated for mutations in a typical SRSCT using the next-generation DNA sequencing approach. An in-frame deletion of 30 nucleotides in the glycogen serine kinase-3 beta phosphorylation region of the ß-catenin gene (CTNNB1) was identified, and the finding was confirmed by Sanger sequencing. This deletion (c.68_97del) at the protein level would lead to a p.Ser23_Ser33delinsThr oncogenic-type mutation. Subsequent immunohistochemistry showed prominent nuclear accumulation of ß-catenin and cyclin D1 in tumor cells. Thus, mutational activation of the Wnt/ß-catenin pathway could be a crucial event in the molecular pathogenesis of SRSCT of the ovary. These findings may also assist in the diagnosis of this rare tumor.

Intranodal palisaded myofibroblastoma: another mesenchymal neoplasm with CTNNB1 (ß-catenin gene) mutations: clinicopathologic, immunohistochemical, and molecular genetic study of 18 cases.

Intranodal palisaded myofibroblastoma is a benign, lymph node-based myofibroblastic tumor of unknown pathogenesis. We report the clinicopathologic, immunohistochemical, and molecular genetic features of this rare entity. The study cohort consisted of 14 men and 4 women ranging in age from 31 to 65 (mean, 47; median 49) years with tumors arising in inguinal lymph nodes (n=15), a neck lymph node (n=1), and undesignated lymph nodes (n=2). Most individuals presented with a painless mass or lump. Possible trauma/injury to the inguinal region was documented in 4 cases. Tumors ranged in size from 1.0 to 4.2 (mean, 3.1; median; 3.0) cm. Microscopically, the process presented as a well-circumscribed, oftentimes pseudoencapsulated nodule (n=17) or nodules (n=1). Tumors consisted of a cellular proliferation of cytologically bland, spindled cells arranged in short fascicles and whorls within a finely collagenous (n=11) or myxocollagenous (n=7) matrix. In 12 tumors, scattered fibromatosis-like fascicles of spindled cells were noted. Histologic features characteristic of the process included nuclear palisades (n=16 cases), collagenous bodies (n=15), and perinuclear intracytoplasmic hyaline globules (n=10). Mitotic activity ranged from 0 to 8 (mean, 2; median, 1) mitotic figures/50 high-powered fields with no atypical division figures identified. Immunohistochemically, all tumors tested expressed smooth muscle actin and/or muscle-specific actin (n=5, each), and nuclear ß-catenin and cyclin D1 (n=8, each). The latter 2 results prompted a screening for mutations in the ß-catenin gene glycogen synthase kinase-3 ß phosphorylation mutational "hotspot" region in exon 3 using polymerase chain reaction amplification and Sanger sequencing. Single nucleotide substitutions leading to missense mutations at the protein level were identified in 7 of 8 (88%) analyzed tumors and are responsible for the abnormal expression of ß-catenin and cyclin D1. These results demonstrate that mutational activation of the ß-catenin gene is likely a pivotal event in the pathogenesis of intranodal palisaded myofibroblastoma.

Nuclear expression and gain-of-function ß-catenin mutation in glomangiopericytoma (sinonasal-type hemangiopericytoma): insight into pathogenesis and a diagnostic marker.

Glomangiopericytoma (sinonasal-type hemangiopericytoma) is a rare mesenchymal neoplasm with myoid phenotype (smooth muscle actin-positive), which distinguishes this tumor from soft tissue hemangiopericytoma/solitary fibrous tumor. Molecular genetic changes underlying the pathogenesis of glomangiopericytoma are not known. In this study, 13 well-characterized glomangiopericytomas were immunohistochemically evaluated for ß-catenin expression. All analyzed tumors showed strong expression and nuclear accumulation of ß-catenin. Following this observation, ß-catenin glycogen serine kinase-3 beta phosphorylation region, encoded by exon 3, was PCR amplified in all cases and evaluated for mutations using Sanger sequencing. Heterozygous mutations were identified in 12 of 13 tumors. All mutations consisted of single-nucleotide substitutions: three in codon 32 (c.94G>C (n=2) and c.95A>T), four in codon 33 (two each c.98C>G and c.98C>T), two in codon 37 (c.109T>G), one in codon 41 (c.121A>G), and two in codon 45 (c.133T>C). At the protein level, these substitutions would lead to p.D32H, p.D32V, p.S33C, p.S33F, p.S37A, p.T41A, and p.S45L mutations, respectively. Previously, similar mutations have been reported in different types of cancers and shown to trigger activation of ß-catenin signaling. All analyzed glomangiopericytomas showed prominent nuclear expression of cyclin D1, as previously shown for tumors with nuclear expression of ß-catenin as a sign of oncogenic activation. These results demonstrate that mutational activation of ß-catenin and associated cyclin D1 overexpression may be central events in the pathogenesis of glomangiopericytoma. In additon, nuclear accumulation of ß-catenin is a diagnostic marker for glomangiopericytoma.

Detection of the BRAF V600E mutation in colon carcinoma: critical evaluation of the imunohistochemical approach.

Recently BRAF V600E mutant-specific antibody (clone VE1) became available to immunohistochemically pinpoint the occurrence of these BRAF-mutant proteins in different tumors, such as colon carcinoma. Detection of BRAF mutations is important for the accurate application of targeted therapy against BRAF serine-threonine kinase activation. In this study, we evaluated 113 colon carcinomas including 95 primary and 27 metastatic tumors with the VE1 antibody using Leica Bond-Max automated immunohistochemistry. To ensure comprehensive BRAF V600E mutation detection, all cases were evaluated using 4 molecular methods (Sanger sequencing, the Cobas 4800 BRAF V600 Mutation Test, BRAF V600 allele-specific polymerase chain reaction, and BRAF V600 quantitative polymerase chain reaction) with nearly 100% concordance. Molecular and immunohistochemical studies were blinded. Furthermore, all cases were evaluated for KRAS and NRAS mutations as parameters mutually exclusive with BRAF mutations offering parallel evidence for BRAF mutation status. Strong to moderate VE1 positivity was seen in 34 tumors. Twelve colon carcinomas showed weak VE1 immunohistochemical staining, and 67 were entirely negative. An identical c.1799T>A single nucleotide substitution leading to the BRAF V600E mutation was identified in 27 of 113 (24%) colon carcinomas. A majority of BRAF-mutant tumors were located in the right side of the colon and had mismatch-repair deficiency. V600E mutation-negative carcinomas were more often sigmoid tumors and usually showed intact mismatch-repair proteins and KRAS or NRAS mutations. The sensitivity and specificity of positive results (strong to moderate staining) of VE1 immunohistochemistry were 85% and 68%, respectively. If any positivity would be considered, then the specificity declined to 51% with no significant improvement of sensitivity. Therefore, only strong positivity should be considered when using the VE1 antibody and Leica Bond-Max automated immunohistochemistry with these parameters. Although VE1 antibody can be useful in the screening of colon carcinomas for BRAF V600E-mutant proteins, molecular genetic confirmation is always necessary for mutation diagnosis.

CD30 expression in malignant vascular tumors and its diagnostic and clinical implications: a study of 146 cases.

Angiosarcoma (AS) is a rare malignant vascular tumor, whereas epithelioid hemangioendothelioma (EHE) is a vascular tumor of low-grade malignancy. CD30 is a member of the tumor necrosis factor receptor superfamily, member 8 (TNFRSF8). Although the expression of CD30 is most commonly associated with lymphoid malignancies or germ cell tumors, occasional ASs have been reported as CD30 positive. However, there are limited data to evaluate its role definitively in malignant vascular tumors. In this study, we evaluated 91 ASs, 30 EHEs from various sites, and 25 Kaposi sarcomas. Overall, CD30 was expressed in 31/91 cases (34%) of AS, in 7/30 cases (30%) of EHE, but in none of the Kaposi sarcomas. CD30 was expressed in a membranous staining pattern and positivity in tumor cells varied from focal to diffuse. The positive ASs included vasoformative more differentiated tumors and also solid, undifferentiated, lymphoma-like examples, one of which was classified as lymphoma before the era of immunohistochemistry. The CD30 expression was seen in >50% of tumor cells in a majority of ASs but only in 7% of EHEs. None of the 55 ASs studied were immunohistochemically positive for TIA-1 or Granzyme B, antigens used as more specific markers for anaplastic large-cell lymphoma. Compared with AS, normal vascular endothelia of capillaries and muscular vessels showed variable positivity. Among hemangiomas, cavernous and spindle cell hemangiomas showed most frequent endothelial CD30 positivity, whereas in most other hemangiomas, CD30 positivity was scant. In conclusion, CD30 expression occurs in a significant subset of ASs and EHEs and needs to be included in the differential diagnosis with other CD30-positive malignancies to avoid a diagnostic pitfall. It remains to be determined whether patients with strongly CD30-positive ASs could be candidates for targeted therapy using the recently introduced CD30 antibody drug conjugates.

Frequent truncating mutations of STAG2 in bladder cancer.

Here we report the discovery of truncating mutations of the gene encoding the cohesin subunit STAG2, which regulates sister chromatid cohesion and segregation, in 36% of papillary non-invasive urothelial carcinomas and 16% of invasive urothelial carcinomas of the bladder. Our studies suggest that STAG2 has a role in controlling chromosome number but not the proliferation of bladder cancer cells. These findings identify STAG2 as one of the most commonly mutated genes in bladder cancer.

No KRAS mutations found in gastrointestinal stromal tumors (GISTs): molecular genetic study of 514 cases.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. A great majority of GISTs is driven by pathological activation of KIT or platelet-derived growth factor receptor-α (PDGFRA), two closely related receptor tyrosine kinases. However, other genetic changes including gain-of-function BRAF mutations and loss of succinate dehydrogenase (SDH) complex activity have been identified in the subsets of KIT-, PDGFRA-wild type tumors. Genetic mutations affecting KIT, PDGFRA, BRAF and SDH complex functions are believed to be mutually exclusive events. Recently, KRAS codon 12 and 13 mutations were reported in a small subset of KIT or PDGFRA mutant GISTs. Moreover, in in vitro experiments, KIT mutants with concurrent KRAS mutation showed resistance to imatinib, a receptor tyrosine kinase inhibitor used in GIST treatment. The aim of this study was to evaluate a large cohort of GISTs to define frequency and clinical significance of KRAS mutations in this type of cancer. A well-characterized cohort of 514 GISTs was screened for KRAS mutations using Sanger sequencing (n=450) and pyrosequencing (n=64). In all, 350 gastric, 100 intestinal and 64 primary disseminated GISTs were analyzed. No KRAS mutations were found. In GIST, KRAS mutations are extremely rare if they exist (<0.2%). Thus, mutational activation of KRAS does not seem to play any significant role in the development and progression of this type of cancer.

Immunohistochemical loss of succinate dehydrogenase subunit A (SDHA) in gastrointestinal stromal tumors (GISTs) signals SDHA germline mutation.

A subset (7% to 10%) of gastric gastrointestinal stromal tumors (GISTs) is notable for the immunohistochemical loss of succinate dehydrogenase (SDH) subunit B (SDHB), which signals the loss of function of the SDH complex consisting of mitochondrial inner membrane proteins. These SDH-deficient GISTs are known to be KIT/PDGFRA wild type, and most patients affected by this subset of GISTs are young. Some of these patients have germline mutations of SDH subunit genes SDHB, SDHC, or SDHD, known as Carney-Stratakis syndrome when combined with paraganglioma. More recently, germline mutations in SDH subunit A gene (SDHA) have also been reported in few patients with KIT/PDGFRA wild-type GISTs. In this study we immunohistochemically examined 127 SDHB-negative and 556 SDHB-positive gastric GISTs and 261 SDHB-positive intestinal GISTs for SDHA expression using a mouse monoclonal antibody 2E3 (Abcam). Cases with available DNA were tested for SDHA, SDHB, SDHC, and SDHD gene mutations using a hybridization-based custom capture next-generation sequencing assay. A total of 36 SDHA-negative GISTs (28%) were found among 127 SDHB-negative gastric GISTs. No SDHB-positive GIST was SDHA negative. Among 7 SDHA-negative tumors analyzed, there were 7 SDHA mutants, most germline. A second hit indicating biallelic inactivation of SDHA was present in 6 of those cases. These patients had no other SDH subunit gene mutations. Among the 25 SDHA-positive, SDHB-negative GISTs analyzed, we identified 3 SDHA mutations (1 germline), and 11 SDHB, SDHC, or SDHD mutations (mostly germline), and 11 patients with no SDH mutations. Compared with patients with SDHA-positive GISTs, those with SDHA-negative GISTs had an older median age (34 vs. 21 y), lower female to male ratio (1.8 vs. 3.1) but similar mitotic counts and median tumor sizes, with a slow course of disease in most cases, despite a slightly higher rate of liver metastases. SDHA-negative GISTs comprise approximately 30% of SDHB-negative/SDH-deficient GISTs, and SDHA loss generally correlates with SDHA mutations.

[An experimental study of the cervical lymphatic imaging in interstitial magnetic resonance lymphography of tongue using Dextran-DTPA-Gd].

PURPOSE: To explore the application value of the cervical lymphatic imaging in interstitial magnetic resonance lymphography using submucosal injection of Dextran-DTPA-Gd. METHODS: 0.2 mL Dextran-DTPA-Gd (3.96 mmol/L) was injected into the submucosa of the bilateral lingual margins in 12 New Zealand rabbits,and then massaged the injection site for 30 seconds. MR images were obtained before injection and 10, 15, 20, 25, 30, 35, 40, 50, 90 minutes after injection by 3D TOF CE-MRA sequence.The signal intensities of cervical lymph node were measured, the enhancing rates(E%) were calculated and the signal enhancing rates -time curve was drawn. The data was analysed using SPSS11.5 software package. RESULTS: The cervical lymph nodes,the first and second lymphatics were strengthened significantly after injecting Dextran-DTPA-Gd, but the blood vessels were not enhanced at the same time. The enhancing rates of cervical lymph node reached the peak(344%) at 30-min,and the best strengthening effect was achieved between 20-min and 50-min. CONCLUSIONS: As IMRLG contrast agent,the Dextran-DTPA-Gd could image lymphatic drainage lines of the neck and the cervical lymph nodes efficiently.

Vascular endothelial growth factor receptor 2 as a marker for malignant vascular tumors and mesothelioma: an immunohistochemical study of 262 vascular endothelial and 1640 nonvascular tumors.

Vascular endothelial growth factor receptor 2 (VEGFR2) is a primary responder to vascular endothelial growth factor signal and thereby regulates endothelial migration and proliferation. This receptor is expressed in endothelial cells and in some vascular tumors, but many reports also detail its expression in carcinomas and lymphomas. VEGFR2 is a potential cell-type marker, and data on VEGFR2 expression may also have therapeutic significance in view of recent availability of VEGFR2 inhibitors. In this study, we immunohistochemically examined 262 vascular endothelial and 1640 nonvascular tumors and selected non-neoplastic tissues with a VEGFR2-specific rabbit monoclonal antibody 55B11. In early human embryo, VEFGR2 was expressed in endothelia of developing capillaries and in the thoracic duct, great vessels, hepatic sinusoids, epidermis, and mesothelia. In late first trimester fetus peripheral soft tissues, VEGFR2 was restricted to capillary endothelia, chondrocytes, and superficial portion of the epidermis. In normal adult tissues, it was restricted to endothelia and mesothelia. VEGFR2 was consistently expressed in angiosarcomas, Kaposi sarcomas, and retiform hemangioendotheliomas. It was detected in only half of epithelioid hemangioendotheliomas (15/27), usually focally. VEGFR2 was strongly expressed in most capillary hemangiomas and weakly or focally in cavernous, venous, and spindle cell hemangiomas and in lymphangiomas. Malignant epithelial mesothelioma was found to be a unique epithelial neoplasm with a strong and nearly consistent VEGFR2 expression, including membrane staining (35/38). Approximately 10% of squamous cell carcinomas and 23% of pulmonary adenocarcinomas contained focal positivity. The only nonendothelial mesenchymal tumors found to be VEGFR2 positive were biphasic synovial sarcoma (focal epithelial expression) and chordoma. All melanomas and lymphomas were negative. VEGFR2 is a promising marker for malignant vascular tumors and malignant epithelioid mesothelioma. Expression in biphasic synovial sarcoma epithelium, chordoma, and some carcinomas has to be considered in differential diagnosis. Information on VEGFR2 tissue expression may be useful in development of targeted oncologic therapy through VEGFR2-specific tyrosine kinase inhibitors.

KBA62 and PNL2: 2 new melanoma markers-immunohistochemical analysis of 1563 tumors including metastatic, desmoplastic, and mucosal melanomas and their mimics.

Identification of metastatic melanoma can be difficult because of its considerable morphologic variation and mimicry of a wide variety of other tumors. The more melanoma-specific melanoma markers, MelanA/MART-1, HMB45, and tyrosinase, used in addition to S100 protein, all have limitations in sensitivity and specificity. In this study, we evaluated 2 new melanoma markers, monoclonal antibodies KBA62 and PNL2 to yet unidentified antigens, using a large panel of metastatic melanomas (n=214), desmoplastic melanomas (n=34), gastrointestinal mucosal melanomas (n=54), benign nevi (n=27), clear cell sarcomas (n=16), and nonmelanocytic tumors (n=1218). Immunoreactivity for KBA62 and PNL2 was found in all pigmented nevi and in 86% and 90% of metastatic melanomas, respectively. Mucosal melanomas showed a similar rate of PNL2 immunoreactivity but somewhat less frequent KBA62 positivity (72%). In addition, KBA62 was found to be a sensitive diagnostic marker for desmoplastic melanoma (28 of 34; 82%), whereas PNL2 was only rarely positive (2 of 34; 6%). KBA62-positive normal tissues included pericytes, vascular and parenchymal smooth muscles, and basal cells of complex epithelia, including myoepithelia, whereas PNL2 labeled only melanocytes and neutrophils. Among nonmelanocytic tumors, those that were KBA62 positive were nodular fasciitis, leiomyoma and leiomyosarcoma, gastrointestinal stromal tumors, benign and malignant nerve sheath tumors, synovial sarcoma, and subsets of various carcinomas, especially those with squamous cell/stratified epithelial differentiation. PNL2 positivity in nonmelanocytic tumors was more restricted but occurred consistently in angiomyolipoma and other perivascular epitheloid cell tumor and in chronic myeloid leukemia tissue infiltrates. KBA62 may assist in the identification of desmoplastic melanomas, but its widespread occurrence in nonmelanomas limits utility. PNL2 is highly specific for melanomas but lacks reactivity with desmoplastic melanomas. It is also an excellent supplementary marker for perivascular epitheloid cell tumor at various sites.

Prox1 transcription factor as a marker for vascular tumors-evaluation of 314 vascular endothelial and 1086 nonvascular tumors.

Prox1, a transcription factor important in the regulation and maintenance of the lymphatic endothelial phenotype, is consistently expressed in lymphangiomas and Kaposi sarcoma and has also been reported in Kaposiform hemangioendothelioma. However, information on its distribution in vascular tumors, such as angiosarcoma, is limited. In this study, we examined selected normal tissues and 314 vascular endothelial and 1086 nonvascular tumors to get an insight into the biology of these tumors and on potential diagnostic use of Prox1 as an immunohistochemical marker. In adult tissues, Prox1 was essentially restricted to lymphatic endothelia, with expression in subsets of pancreatic and gastrointestinal epithelia. However, it was also detected in embryonic liver and heart. Prox1 was consistently expressed in lymphangiomas, venous hemangiomas, Kaposi sarcoma, in endothelia of spindle cell hemangioma, Kaposiform hemangioendothelioma, and retiform hemangioendothelioma, and in half of epithelioid hemangioendotheliomas. It was present in most cutaneous angiosarcomas from different sites but was less commonly expressed in deep soft tissue and visceral angiosarcomas. In contrast, Prox1 was generally absent in capillary and cavernous hemangiomas. In positive hemangiomas and angiosarcomas it was coexpressed with podoplanin, another marker of the lymphatic endothelial phenotype. There was an inverse correlation with CD34 expression. The expression in mesenchymal nonendothelial neoplasm was limited. Prox1 was detected in 5 of 27 synovial sarcomas, specifically in the epithelia of biphasic tumors. Four of 16 Ewing sarcomas and 5 of 15 paragangliomas were also positive. All melanomas and undifferentiated sarcomas were negative. Among epithelial neoplasms, Prox1 was detected in 18 of 38 colonic carcinomas and 10 of 15 cholangiocarcinomas and in a minority of pulmonary, prostatic, and endometrial adenocarcinomas. The common Prox1 expression in angiosarcoma and its rare presence in nonvascular mesenchymal tumors make this marker suitable for the diagnosis of angiosarcoma and Kaposi sarcoma. However, the presence of Prox1 in some malignant epithelial tumors necessitates caution in applying Prox1 as a marker for vascular tumors. Common Prox1 expression in angiosarcoma may reflect the lymphatic endothelial phenotype in these tumors. Its patterns of expression in hemangiomas and angiosarcoma may be diagnostically useful and offer a new parameter in the biological classification of vascular tumors.

Claudin-5 as an immunohistochemical marker for angiosarcoma and hemangioendotheliomas.

Claudin-5 is a tight junction protein expressed in endothelial cells and in some epithelial cells. It has been shown as a marker in canine angiosarcoma; however, data on human mesenchymal tumors are limited. In this study, we examined claudin-5 in selected normal tissues, in 280 benign and malignant vascular tumors, and in 448 other epithelial, mesenchymal, and neuroectodermal tumors. Early human embryos showed limited claudin-5 expression in endothelia of large truncal vessels, in liver sinusoids, and in the epidermis. In adult human tissues, claudin-5 was widely present in the endothelia of vessels of different calibers. However, neovascular capillaries in carcinomas and other tumors were often negative. Claudin-5 was also present in many glandular and ductal epithelia, hair shafts, and glomerular podocytes. Capillary and cavernous hemangiomas and lymphangiomas generally showed endothelial positivity; however, many vessels, especially those with poorly formed lumina, were negative in juvenile capillary hemangiomas, and fewer vessels were highlighted in lobular capillary hemangiomas. Hemangioendotheliomas of retiform, kaposiform, epithelioid, and epithelioid sarcoma-like types showed positivity, the latter in a diffuse cytoplasmic manner. Most angiosarcomas (115 of 119) and Kaposi sarcomas (28 of 29) showed strong labeling, but rare cases only contained positive cytoplasmic dots. Claudin-5 was commonly present in carcinomas (except in sarcomatoid ones), but most tumors showed heterogenous labeling weaker than that in angiosarcomas. Seminomas and renal cell, hepatocellular, and signet ring cell carcinomas were negative. Among non-vascular mesenchymal tumors, biphasic synovial sarcoma was the only tumor to contain claudin-5-positive nonvascular elements. In hemangiopericytomas, glomus tumor, and melanomas, claudin-5 was expressed in endothelial cells only. Claudin-5 is a promising new marker for angiosarcomas and hemangioendotheliomas, but widespread expression in carcinomas and biphasic synovial sarcoma should be considered in the differential diagnosis and addressed with the use of an antibody panel including keratins, especially the more epithelial-specific AE1/AE3 and epithelial membrane antigen.

Succinate dehydrogenase-deficient GISTs: a clinicopathologic, immunohistochemical, and molecular genetic study of 66 gastric GISTs with predilection to young age.

Most gastrointestinal stromal tumors (GISTs) are driven by KIT or PDGFRA-activating mutations, but a small subset is associated with loss of function of the succinate dehydrogenase (SDH) complex of mitochondrial inner membrane proteins. This occurs by germline mutations of the SDH subunit genes and hitherto unknown mechanisms. SDH-deficient GISTs especially include pediatric GISTs and those associated with Carney triad (CT) or Carney-Stratakis syndromes (CSSs); the latter 2 also include paraganglioma as a component. SDH-deficient GISTs were identified in this study on the basis of immunohistochemical loss of succinate dehydrogenase subunit B (SDHB), which signals functional loss of the SDH complex. We found 66 SDH-deficient GISTs among 756 gastric GISTs, with an estimated frequency of 7.5% of unselected cases. Nearly, all gastric GISTs in patients <20 years, and a substantial percentage of those in patients <40 years, but only rare GISTs in older adults were SDH deficient. There was a female predominance of over 2:1. Two patients each had either pulmonary chondroma or paraganglioma (CT), but none of the examined cases had SDH germline mutations (CSS) or somatic KIT/PDGFRA or BRAF mutations. SDH-deficient GISTs were often multiple and typically showed plexiform muscularis propria involvement and epithelioid hypercellular morphology. They were consistently KIT-positive and DOG1/Ano 1-positive and almost always smooth muscle actin negative. Tumor size and mitotic activity varied, and the tumors were somewhat unpredictable with low mitotic rates developing metastases. Gastric recurrences occurred in 11 patients, and peritoneal and liver metastases occurred in 8 and 10 patients, respectively. Lymph node metastases were detected in 5 patients, but lymphovascular invasion was present in >50% of cases studied; these 2 were not related to adverse outcome. Seven patients died of disease, but many had long survivals, even with peritoneal or liver metastases. All 378 nongastric GISTs and 34 gastric non-GIST mesenchymal tumors were SDHB positive. SDH-deficient GISTs constitute a small subgroup of gastric GISTs; they usually occur in children and young adults, often have a chronic course similar to that of pediatric and CT GISTs, and have potential association with paraganglioma, necessitating long-term follow-up.

ERG transcription factor as an immunohistochemical marker for vascular endothelial tumors and prostatic carcinoma.

ERG, an ETS family transcription factor, is known to be expressed in endothelial cells, and oncogenic ERG gene fusions occur in subsets of prostatic carcinoma, acute myeloid leukemia, and Ewing sarcoma. In this study, we immunohistochemically investigated nuclear ERG expression using a new monoclonal antibody, CPDR ERG-MAb, that is highly specific for detecting ERG protein and ERG-expressing prostate carcinomas. A broad range of vascular endothelial (n = 250), other mesenchymal (n = 973), and epithelial tumors (n = 657) was examined to determine the use of ERG immunohistochemistry in surgical pathology. Only immunostains with ERG-positive normal endothelia (internal control) were considered valid, and only nuclear staining was considered to be positive. In adult tissues, ERG was restricted to endothelial cells and to a subset of bone marrow precursors, but early fetal mesenchyme and subpopulations of fetal cartilage were also positive. In vascular tumors, ERG was expressed in endothelia of all hemangiomas and lymphangiomas, and typically extensively expressed in 96 of 100 angiosarcomas, 42 of 43 epithelioid hemangioendotheliomas, and all 26 Kaposi sarcomas. Among nonvascular mesenchymal tumors, only blastic extramedullary myeloid tumors (7 of 10) and rare Ewing sarcomas (2 of 29) were positive. Among epithelial tumors, 30 of 66 prostatic adenocarcinomas showed focal-to-extensive ERG positivity, with no immunoreactivity in the normal prostate. Other carcinomas and epithelial tumors (n = 643) were ERG negative, with the exception of 1 of 42 large cell undifferentiated pulmonary carcinomas and 1 of 27 mesotheliomas, each of which showed focal nuclear ERG positivity. On the basis of the above observations, ERG is a highly specific new marker for benign and malignant vascular tumors. Among epithelial tumors, ERG shows a great promise as a marker to identify prostatic carcinoma in both primary and metastatic settings.