[Glomuvenous malformation: a clinicopathological analysis of 31 cases].

Objective: To investigate the clinicopathological features of glomuvenous malformation (GVM). Methods: Thirty-one cases of GVM diagnosed at the Henan Provincial People's Hospital from January 2011 to December 2021 were collected. Their clinical and pathological features were analyzed. The expression of relevant markers was examined using immunohistochemistry. The patients were also followed up. Results: There were 16 males and 15 females in this study, with an average age of 11 years (range, 1-52 years). The locations of the disease included 13 cases in the limbs (8 cases in the upper limbs, 5 cases in the lower limbs), 9 cases in the trunks, and 9 cases in the foot (toes or subungual area). Twenty-seven of the cases were solitary and 4 were multifocal. The lesions were characterized by blue-purple papules or plaques on the skin surface, which grew slowly. The lumps became larger and appeared to be conspicuous. Microscopically, GVM mainly involved the dermis and subcutaneous tissue, with an overall ill-defined border. There were scattered or clustered irregular dilated vein-like lumens, with thin walls and various sizes. A single or multiple layers of relatively uniform cubic/glomus cells were present at the abnormal wall, with scattered small nests of the glomus cells. The endothelial cells in the wall of abnormal lumen were flat or absent. Immunohistochemistry showed that glomus cells strongly expressed SMA, h-caldesmon, and collagen IV. Malformed vascular endothelial cells expressed CD31, CD34 and ERG. No postoperative recurrence was found in the 12 cases. Conclusions: GVM is an uncommon type of simple venous malformation in the superficial soft tissue and different from the classical glomus tumor. Morphologically, one or more layers of glomus cells grow around the dilated venous malformation-like lumen, which can be combined with common venous malformations.

Update on Pheochromocytoma and Paraganglioma from the SSO Endocrine/Head and Neck Disease-Site Work Group. Part 1 of 2: Advances in Pathogenesis and Diagnosis of Pheochromocytoma and Paraganglioma.

This first part of a two-part review of pheochromocytoma and paragangliomas (PPGLs) addresses clinical presentation, diagnosis, management, treatment, and outcomes. In this first part, the epidemiology, prevalence, genetic etiology, clinical presentation, and biochemical and radiologic workup are discussed. In particular, recent advances in the genetics underlying PPGLs and the recommendation for genetic testing of all patients with PPGL are emphasized. Finally, the newer imaging methods for evaluating of PPGLs are discussed and highlighted.

Structure of a glomulin-RBX1-CUL1 complex: inhibition of a RING E3 ligase through masking of its E2-binding surface.

The approximately 300 human cullin-RING ligases (CRLs) are multisubunit E3s in which a RING protein, either RBX1 or RBX2, recruits an E2 to catalyze ubiquitination. RBX1-containing CRLs also can bind Glomulin (GLMN), which binds RBX1's RING domain, regulates the RBX1-CUL1-containing SCF(FBW7) complex, and is disrupted in the disease Glomuvenous Malformation. Here we report the crystal structure of a complex between GLMN, RBX1, and a fragment of CUL1. Structural and biochemical analyses reveal that GLMN adopts a HEAT-like repeat fold that tightly binds the E2-interacting surface of RBX1, inhibiting CRL-mediated chain formation by the E2 CDC34. The structure explains the basis for GLMN's selectivity toward RBX1 over RBX2, and how disease-associated mutations disrupt GLMN-RBX1 interactions. Our study reveals a mechanism for RING E3 ligase regulation, whereby an inhibitor blocks E2 access, and raises the possibility that other E3s are likewise controlled by cellular proteins that mask E2-binding surfaces to mediate inhibition.

The glomuvenous malformation protein Glomulin binds Rbx1 and regulates cullin RING ligase-mediated turnover of Fbw7.

Fbw7, a substrate receptor for Cul1-RING-ligase (CRL1), facilitates the ubiquitination and degradation of several proteins, including Cyclin E and c-Myc. In spite of much effort, the mechanisms underlying Fbw7 regulation are mostly unknown. Here, we show that Glomulin (Glmn), a protein found mutated in the vascular disorder glomuvenous malformation (GVM), binds directly to the RING domain of Rbx1 and inhibits its E3 ubiquitin ligase activity. Loss of Glmn in a variety of cells, tissues, and GVM lesions results in decreased levels of Fbw7 and increased levels of Cyclin E and c-Myc. The increased turnover of Fbw7 is dependent on CRL and proteasome activity, indicating that Glmn modulates the E3 activity of CRL1(Fbw7). These data reveal an unexpected functional connection between Glmn and Rbx1 and demonstrate that defective regulation of Fbw7 levels contributes to GVM.

Paragangliomas in Carney-Stratakis Syndrome.

Carney-Stratakis Syndrome (CSS) comprises of paragangliomas (PGLs) and gastrointestinal stromal tumors (GISTs). Several of its features overlap with Carney Triad (CT) - PGLs, GISTs, and pulmonary chondromas. CSS has autosomal dominant inheritance, incomplete penetrance, and greater relative frequency of PGL over GISTs. The PGLs in CSS are multicentric and GISTs are multifocal in all the patients, suggesting an inherited susceptibility and associating the two manifestations. In this review, we highlight the clinical, pathological, and molecular characteristics of CSS, along with its diagnostic and therapeutic implications.

PHEOCHROMOCYTOMA: A GENETIC AND DIAGNOSTIC UPDATE.

OBJECTIVE: Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumors derived from adrenal or extra-adrenal locations, respectively. Upon suspicion of PPGL, specific metabolomic, molecular, biochemical, imaging, and histopathologic studies are performed to prove, localize, treat, and monitor disease progression. Improved diagnostic tools allow physicians to accurately diagnose PPGL, even in patients presenting with small (<1 cm) or biochemically silent tumors, which previously delayed proper detection and treatment. METHODS: This review outlines the most updated approach to PPGL patients and presents a new diagnostic protocol for physicians to increase earlier tumor identification and accurately assess metastatic behavior. CONCLUSION: We present the most recent advances in genetics, epigenetics, metabolomics, biochemical, and imaging diagnoses of this rare tumor to properly assess disease, decide treatment options, and manage follow-up. We also elaborate on new therapeutic perspectives in these very rare neoplastic entities. ABBREVIATIONS: ATRX = ATRX chromatin remodeler; ccRCC = clear cell renal cell carcinoma; c-MYC = MYC proto oncognene; CT = computed tomography; DOTATATE = DOTA-octreotate; EGLN1/2 = egl-9 family hypoxia inducible factor 1/2; EGLN2/PHD1 = egl-9 family hypoxia inducible factor 2; EPAS1/HIF2A = endothelial PAS domain protein 2/hypoxia-inducible factor 2α; ERK = extracellular signal-regulated kinase; HIFs = hypoxia-inducible factors; HIF-α = hypoxia-inducible factor alpha; HNPGLs = head and neck paragangliomas; 177Lu-DOTATATE = lutetium octreotate; MAX = myc-associated factor X; MDH2 = malate dehydrogenase; MIBG = metaiodobenzylguanidine; MN = metanephrine; MRI = magnetic resonance imaging; mTOR = mammalian target of rapamycin; NETs = neuroendocrine tumors; NF1 = neurofibromin 1; NMN = normetanephrine; PHD = prolyl hydroxylase domain protein; PI3K = phosphoinositide 3-kinase; PPGLs = pheochromocytoma and paragangliomas; PRRT = peptide receptor radionuclide therapy; Pvhl = von Hippel-Lindau protein; RAS = rat sarcoma oncogene; RET = rearranged during transfection proto-oncogene; SDH = succinate dehydrogenase; SDHA, -B, -C, -D = succinate dehydrogenase subunits A, B, C, D; SDHAF2 = succinate dehydrogenase complex assembly factor 2; SDHB, C, D = succinate dehydrogenase subunits B, C, D; SDHx = succinate dehydrogenase subunits; SSTRs = somatostatin receptors; VHL = von Hippel-Lindau.

Ultrastructural features of tumor-associated mast cells in parasympathetic paragangliomas (chemodectomas) of the neck.

The mechanisms of the pathogenesis of neck paraganglioma (PGL) and the possible role of mast cells (MCs) in its development and metastasis are still poorly understood. We analyzed MCs' morphologic characterization, activation, and the properties of their cytoplasmic/released granules in PGLs, using light and transmission electron microscopy. Paragangliomas showed a large tumor-associated MC population both in the connective tissue layers of the tumor and between the tumor cells. Notably, MCs were presented by a high expression of specific proteases, size variation, polymorphism, and variable ultrastructural phenotype of granules. A massive number of granules were released surrounding the degranulated MCs while the integrity of MC membrane was maintained. Granules were electron-dense with or without a membrane, ranging from 0.2 to 0.8 µm in diameter. MC plasmalemma was not found at the site of MC-collagen fibrils contact, whereas the secretome and fibrils were directly contacted. We observed direct and mediator-based interactions between MCs and paraganglioma cells. The latter preserved their membrane integrity when MC granules were not in proximity. The effects of the MC secretome on the paraganglioma microenvironment demonstrated its pathogenetic role in tumor progression and allow its application to new diagnostic criteria and the development of protocols for personalized therapy. RESEARCH HIGHLIGHTS: Ultrastructural analysis reveals novel regulatory effects of mast cells via diverse secretory pathways on the pathogenesis of parasympathetic paraganglioma, including fibrous extracellular matrix remodeling and mediator-based interactions between MCs and cells of the tumor microenvironment.

[Expression of SDHB, EPAS1 and MIB-1 in Zuckerkandl paragangliomas].

OBJECTIVE: To explore the significance of succinate dehydrogenase B (SDHB) mutation and EPAS1 overexpression in Zuckerkandl paragangliomas (PGL) and examine their correlations with malignant infiltration and metastasis. METHODS: From March 2008 to July 2011, the clinical profiles of 16 Zuckerkandl PGL patients were analyzed retrospectively. For increased diagnostic specificity, a complex immunohistochemical panel of tissue microarray was performed for SDHB, EPAS1 and MIB-1. Positive expression identified as a granular cytoplasmic staining. Greater than or equal to 50% as strongly positive (+++), 1% to 10% as weakly positive (+). RESULTS: Tissue microarray immunohistochemical staining showed SDHB immunoreactivity in the cytoplasm, whereas EPAS1 and MIB-1 in the nuclear of tumor cells. Positive expression of EPAS1 in which 13 cases of Zuckerkandl PGL. And high expression strongly associated with malignancy. SDHB mutation of 7 cases are all EPAS1 positive staining. Non-gene mutation 9 cases tumor specimens, 6 cases were EPAS1 positive expression (P < 0.05). CgA positive expression in 11 cases benign Zuckerkandl PGL, strongly positive in 4 malignant cases (4/4). MIB-1 below 1% in 12 cases of benign Zuckerkandl PGL. And in 4 malignant cases, MIB-1 was about 3%. Malignant neoplasms had significantly higher EPAS1, CgA and MIB-1 expression compared to benign counterparts (P < 0.05). CONCLUSIONS: The SDHB mutation causes the EPAS1 over expression in PGL and correlation with higher positive expression of CgA and MIB-1. It may be one of the mechanisms of malignant invasiveness and metastasis in PGL.

Adrenal cortical tumors, pheochromocytomas and paragangliomas.

Distinguishing adrenal cortical adenomas from carcinomas may be a difficult diagnostic problem. The criteria of Weiss are very useful because of their reliance on histologic features. From a practical perspective, the most useful criteria to separate adenomas from carcinomas include tumor size, presence of necrosis and mitotic activity including atypical mitoses. Adrenal cortical neoplasms in pediatric patients are more difficult to diagnose and to separate adenomas from carcinomas. The diagnosis of pediatric adrenal cortical carcinoma requires a higher tumor weight, larger tumor size and more mitoses compared with carcinomas in adults. Pheochromocytomas are chromaffin-derived tumors that develop in the adrenal gland. Paragangliomas are tumors arising from paraganglia that are distributed along the parasympathetic nerves and sympathetic chain. Positive staining for chromogranin and synaptophysin is present in the chief cells, whereas the sustentacular cells are positive for S100 protein. Hereditary conditions associated with pheochromocytomas include multiple endocrine neoplasia 2A and 2B, Von Hippel-Lindau disease and neurofibromatosis I. Hereditary paraganglioma syndromes with mutations of SDHB, SDHC and SDHD are associated with paragangliomas and some pheochromocytomas.

Comparison of [¹¹¹In]pentetreotide-SPECT and [¹8F]FDOPA-PET in the localization of extra-adrenal paragangliomas: the case for a patient-tailored use of nuclear imaging modalities.

AIMS AND METHODS: The aim of this prospective study was to compare the diagnostic value of [¹8F]FDOPA-PET and [¹¹¹In]pentetreotide-SPECT somatostatin receptor scintigraphy (SRS) in patients with nonmetastatic extra-adrenal paragangliomas (PGLs). Twenty-five consecutive unrelated patients who were known or suspected of having nonmetastatic extra-adrenal PGLs were prospectively evaluated with SRS and [¹8F]FDOPA-PET. ¹³¹I-MIBG and [¹8F]FDG-PET were added to the work-up in patients with a personal or familial history of PGL, predisposing mutations, abdominal PGLs, metanephrine hypersecretion and abdominal foci on SRS and/or [¹8F]FDOPA-PET. RESULTS: SRS correctly detected 23/45 lesions of which 20 were head or neck lesions (H&N) and 3 were abdominal lesions. [¹8F]FDOPA-PET detected significantly more lesions than SRS (39/45, P < 0·001). Both SRS and ¹8F-DOPA-PET detected significantly more H&N than abdominal lesions (66·7% vs 20%, P = 0·003 and 96·7% vs 67%, P = 0·012, respectively). In two patients with the succinate dehydrogenase D (SDHD) mutation, [¹8F]FDOPA-PET missed five abdominal PGLs which were detected by the combination of SRS, [¹³¹I]MIBG and [¹8F]FDG-PET. A lesion-based analysis using a forward stepwise logistic regression model demonstrates that size ≤ 10 mm (P = 0·002) and abdominal lesions (P = 0·031) were independently associated with "[¹8F]FDOPA-PET diagnosis only". In turn, a previous history of surgery and/or the presence of germline mutation was associated with lower lesion size (P = 0·001). CONCLUSIONS: The sensitivity of SRS for localizing parasympathetic PGLs is lower than originally reported, and [¹8F]FDOPA-PET is better than SRS for localizing small lesions. SRS should be replaced by [¹8F]FDOPA-PET as the first-line imaging procedure in H&N PGL, especially in patients at risk of multifocal disease (predisposing mutations and or previous history of surgery).

A novel mutation of the glomulin gene in an Italian family with autosomal dominant cutaneous glomuvenous malformations.

Glomuvenous malformations (GVM) are hamartomas characterized histologically by glomus cells, which should be distinguished from glomus tumors. Familial GVM are rare, often present as multiple lesions, and exhibit familial aggregation, with autosomal dominant transmission. GVM are caused by mutations of the glomulin (GLMN) gene on chromosome 1p21-p22. Their development is thought to follow the 'two-hit' hypothesis, with a somatic mutation required in addition to the inherited germline mutation. We describe a novel GLMN mutation in an Italian family with GVM in which some members present with the less commonly observed phenotype of solitary lesions. A second somatic 'hit' mutation in GLMN was not discovered in our family. We further provide histological, immunohistochemical and electron microscopic data exhibiting the classic features of GVM. The diagnosis of GVM is critical because of distinction from venous malformations and blue rubber bleb nevus syndrome, which may demonstrate clinical similarities but require different treatment.

Immunohistochemical Expression of Choline Acetyltransferase and Catecholamine-Synthesizing Enzymes in Head-and-Neck and Thoracoabdominal Paragangliomas and Pheochromocytomas.

Paragangliomas (PGLs) are neural-crest-derived, non-epithelial neuroendocrine tumors distributed along the parasympathetic and sympathetic nerves. Head-and-neck PGLs (HNPGLs) have been recognized as nonchromaffin, nonfunctional, parasympathetic tumors. By contrast, thoracoabdominal paragangliomas and pheochromocytomas (PPGLs) are chromaffin, functional, sympathetic tumors. Although HNPGLs and PPGLs have the same histological structure, the zellballen pattern, composed of chief and sustentacular cells surrounded by abundant capillaries, the pathobiological differences between these types of PGLs remain unclarified. To determine the phenotypic features of these PGLs, we performed an immunohistochemical study using specific antibodies against choline acetyltransferase (ChAT), an enzyme involved in acetylcholine synthesis, and enzymes for the catecholamine-synthesis, tyrosine hydroxylase (TH), and dopamine beta-hydroxylase (DBH), in 34 HNPGLs from 31 patients, 12 thoracoabdominal PGLs from 12 patients, and 26 pheochromocytomas from 22 patients. The expression of ChAT, TH, and DBH was 100%, 23%, and 10% in the HNPGLs; 12%, 100%, and 100% in the pheochromocytomas; and 25%, 67%, and 100% in the thoracoabdominal PGLs, respectively. These results designate HNPGLs as acetylcholine-producing parasympathetic tumors, in contrast to PPGLs being catecholamine-producing tumors. The other most frequently used neuroendocrine markers are synaptophysin and chromogranin A expressed 100% and 80%, respectively, and synaptophysin was superior to chromogranin A in HNPGLs. This is the first report of HNPGLs being acetylcholine-producing tumors. Immunohistochemistry of ChAT could be greatly useful for pathologic diagnosis of HNPGL. Whether measurement of acetylcholine levels in the blood or urine could be a tumor marker of HNPGLs should be investigated soon.

SDHC Methylation Pattern in Patients With Carney Triad.

Carney triad is a multitumor syndrome affecting almost exclusively young women in a nonfamilial setting, which manifests by multifocal gastric gastrointestinal stromal tumors, paragangliomas, and pulmonary chondroma. The Carney triad-associated tumors are characterized by a deficiency of the mitochondrial succinate dehydrogenase enzymatic complex. Recently, it has been observed that the deficiency results from epigenetic silencing of the SDHC gene by its promoter hypermethylation. To elucidate anatomic distribution of SDHC promoter methylation in Carney triad patients and thus to shed some light on the possible natural development of this epigenetic change, both neoplastic and available non-neoplastic tissues of 3 patients with Carney triad were tested for hypermethylation at the SDHC promoter site. SDHC promoter hypermethylation was proven in all tumors studied. Lack of SDHC epigenetic silencing in the non-neoplastic lymphoid and duodenal tissue (ie, tissues not involved in the development of Carney triad-associated tumors) together with the finding of SDHC promoter hypermethylation in the non-neoplastic gastric wall favors the hypothesis of postzygotic somatic mosaicism as the biological background of Carney triad; it also offers an explanation of the multifocality of gastrointestinal stromal tumors of the stomach occurring in this scenario as well. However, the precise mechanism responsible for the peculiar organ-specific distribution of Carney triad-associated tumors is still unknown.

Orbital paraganglioma--a case report and review of the literature.

Paragangliomas are unique neuroendocrine neoplasms arising in specialized neural crest cells and may be adrenal or extra-adrenal. Paragangliomas have been described in various unusual locations, e.g., urinary bladder, prostate, cauda equina, larynx, sellar region, thyroid gland and nasal cavity. Orbital paragangliomas are very rare and peculiar in histogenesis as the orbit is a site in which the existence of normal paraganglia is not well-documented in humans. We hereby report a case of an orbital paraganglioma in a 70-year-old female patient, the oldest patient reported so far.

A 46-Year-Old Woman With a Mediastinal Mass.

CASE PRESENTATION: A 46-year-old otherwise healthy woman visited the ED twice over a period of 4 days for chest discomfort, midback pain, and dyspnea. The pain was localized, constant, nonpleuritic in nature, moderate in severity, and was not relieved by over-the-counter medications.

Pheochromocytomas and extra-adrenal paragangliomas detected by screening in patients with SDHD-associated head-and-neck paragangliomas.

Patients with SDHD-associated head-and-neck paragangliomas (HNP) are at risk for developing pheochromocytomas for which screening has been advised. To assess clinical, biochemical, and radiological outcomes of screening in a large single-center cohort of SDHD-positive patients with HNP and to address the necessity for repetitive follow-up, we evaluated 93 patients with SDHD-associated HNP (p.Asp92Tyr, p.Leu139Pro). Screening consisted of measurement of 24 h urinary excretion of catecholamines and/or their metabolites in duplicate, which was repeated with intervals of 2 years if initial biochemical screening was negative. In patients, in whom urinary excretion was above the reference limit, imaging studies with (123)I-MIBG (metaiodobenzylguanidine) scintigraphy and magnetic resonance imaging (MRI) and/or computed tomography (CT) were performed. Pheochromocytomas and extra-adrenal paragangliomas were treated surgically after appropriate blockade. Median follow-up was 4.5 years (range 0.5-19.5 years). Twenty-eight out of the 93 patients were included in our study and underwent additional imaging for pheochromocytomas/extra-adrenal paragangliomas. In 11 out of the 28 patients intra-adrenal pheochromocytomas were found. Extra-adrenal paragangliomas were discovered in eight patients. These tumors were detected during initial screening in 63% of cases, whereas 37% were detected after repeated biochemical screening. One patient was diagnosed with a biochemically silent pheochromocytoma. The high prevalence of pheochromocytomas/extra-adrenal paragangliomas in patients with SDHD-associated HNP warrants regular screening for tumors in these patients. Paragangliomas that do not secrete catecholamines might be more prevalent than previously reported. Future studies will have to establish whether routine imaging studies should be included in the screening of SDHD mutation carriers, irrespective of biochemical screening.

Contrasting clinical manifestations of SDHB and VHL associated chromaffin tumours.

Mutations in succinate dehydrogense-B (SDHB) and the von Hippel-Lindau (VHL) genes result in an increased risk of developing chromaffin tumours via a common aetiological pathway. The aim of the present retrospective study was to compare the clinical phenotypes of disease in subjects developing chromaffin tumours as a result of SDHB mutations or VHL disease. Thirty-one subjects with chromaffin tumours were assessed; 16 subjects had SDHB gene mutations and 15 subjects had a diagnosis of VHL. VHL-related tumours were predominantly adrenal phaeochromocytomas (22/26; 84.6%), while SDHB-related tumours were predominantly extra-adrenal paragangliomas (19/25; 76%). Median age at onset of the first chromaffin tumour was similar in the two cohorts. Tumour size was significantly larger in the SDHB cohort in comparison with the VHL cohort (P=0.002). Multifocal disease was present in 9/15 (60%) of the VHL cohort (bilateral phaeochromocytomas) and only 3/16 (19%) of the SDHB cohort, while metastatic disease was found in 5/16 (31%) of the SDHB cohort but not in the VHL cohort to date. The frequency of symptoms, hypertension and the magnitude of catecholamine secretion appeared to be greater in the SDHB cohort. Renal cell carcinomas were a feature in 5/15 (33%) of the VHL cohort and 1/16 (6%) of the SDHB cohort. These data indicate that SDHB-related tumours are predominantly extra-adrenal in location and associated with higher catecholamine secretion and more malignant disease, in subjects who appear more symptomatic. VHL-related tumours tend to be adrenal phaeochromocytomas, frequently bilateral and associated with a milder phenotype.

Paraganglioma of the thyroid gland: a rare entity.

Paragangliomas are neuroendocrine tumors. The thyroid gland is one of the anatomic sites in which paraganglia are not normally located and are exceptionally rare. We report a case of a 36-year-old Hispanic woman with a soft mass measuring about 30 mm in the right thyroid lobe. Patient was operated on and the neoplasm showed microscopically a typical nesting organoid pattern (zellballen). The inmunohistochemical analysis revealed that the tumor showed strongly and diffuse stain for NSE, Synaptophysin, Chromogranin A, and S-100 protein in the sustentacular cells, whereas no inmunoreactivity was detected with antibodies against thyroglobulin, calcitonin, TTF-1, CEA, and AE1-AE3. The MIB-1 labeling showed 7% of neoplastic cells. Head and neck paragangliomas usually develop slowly, and this tumor exhibited a low proliferative activity. In view of the uncertain malignant potential of paragangliomas, we recommended a careful long-term follow-up.

Extra-adrenal paraganglioma: presentation in three uncommon locations.

Extra-adrenal paragangliomata are uncommon entities. They can be classified into four basic groups according to their anatomical sites, i.e. branchiomeric, intravagal, aorticosympathetic and visceral autonomic. Similar tumours may arise in sites away from the usual distribution of the sympathetic and parasympathetic ganglia, e.g. orbit, nose, small intestine and even in the pancreas. We report three instructive cases of extra-adrenal paraganglioma which were found in unusual sites such as urinary bladder, thyroid gland and on the wall of the inferior vena cava.

Frequency and extent of cytokeratin expression in paraganglioma: an immunohistochemical study of 60 cases from 5 anatomic sites and review of the literature.

The absence of cytokeratin expression in paraganglioma helps to differentiate it from other neuroendocrine neoplasms such as carcinoid tumor. Although rare cytokeratin positive paragangliomas have been reported, there are no large systematic studies of this phenomenon. The aim of this study was to determine the frequency and extent of cytokeratin expression in paragangliomas using a large cohort of cases from multiple anatomic sites. Immunohistochemical staining for keratin AE1/AE3 (mouse monoclonal, MAB3412; Millipore) and CAM 5.2 (mouse monoclonal, 349 205; Becton-Dickinson) was performed on whole-tissue sections from 60 resected paragangliomas from the head and neck (36), thorax (10), abdomen (8), intradural/epidural spine (5) and bone, left iliac (1). Cytokeratin expression was identified in only 2/60 (3.3%) cases. One was a mediastinal paraganglioma with moderate to strong expression of keratin AE1/AE3 and CAM 5.2 in <5% tumor cells. The other was a lumbar intradural paraganglioma positive for CAM 5.2 (moderate to strong, 80% of tumor cells) but negative for keratin AE1/AE3. All other paragangliomas (58/60, 96.7%) were negative for keratin AE1/AE3 and CAM 5.2. This study - the largest series of cytokeratin-stained whole-tissue sections of paragangliomas to date - supports the dictum that most paragangliomas are cytokeratin negative. Rare exceptions may be site-related.