Impaired catabolism of free oligosaccharides due to MAN2C1 variants causes a neurodevelopmental disorder.

Free oligosaccharides (fOSs) are soluble oligosaccharide species generated during N-glycosylation of proteins. Although little is known about fOS metabolism, the recent identification of NGLY1 deficiency, a congenital disorder of deglycosylation (CDDG) caused by loss of function of an enzyme involved in fOS metabolism, has elicited increased interest in fOS processing. The catabolism of fOSs has been linked to the activity of a specific cytosolic mannosidase, MAN2C1, which cleaves α1,2-, α1,3-, and α1,6-mannose residues. In this study, we report the clinical, biochemical, and molecular features of six individuals, including two fetuses, with bi-allelic pathogenic variants in MAN2C1; the individuals are from four different families. These individuals exhibit dysmorphic facial features, congenital anomalies such as tongue hamartoma, variable degrees of intellectual disability, and brain anomalies including polymicrogyria, interhemispheric cysts, hypothalamic hamartoma, callosal anomalies, and hypoplasia of brainstem and cerebellar vermis. Complementation experiments with isogenic MAN2C1-KO HAP1 cells confirm the pathogenicity of three of the identified MAN2C1 variants. We further demonstrate that MAN2C1 variants lead to accumulation and delay in the processing of fOSs in proband-derived cells. These results emphasize the involvement of MAN2C1 in human neurodevelopmental disease and the importance of fOS catabolism.

Cross-reactivity of the BRAF VE1 antibody with epitopes in axonemal dyneins leads to staining of cilia.

Antibodies that recognize neo-epitopes in tumor cells are valuable tools in the evaluation of tissue biopsy or resection specimens. The VE1 antibody that recognizes the V600E-mutant BRAF protein is one such example. We have recently shown that the vast majority of papillary craniopharyngiomas-tumors that arise in the sellar or suprasellar regions of the brain-harbor BRAF V600E mutations. The VE1 antibody can be effective in discriminating papillary craniopharyngioma from adamantinomatous craniopharyngioma, which harbors mutations in CTNNB1 and not BRAF. While further characterizing the use of the VE1 antibody in the differential diagnosis of suprasellar lesions, we found that the VE1 antibody stains the epithelial cells lining Rathke's cleft cysts with very strong staining of the cilia of these cells. We used targeted sequencing to show that Rathke's cleft cysts do not harbor the BRAF V600E mutation. Moreover, we found that the VE1 antibody reacts strongly with cilia in various structures-the bronchial airways, the fallopian tubes, the nasopharynx, and the epididymis-as well as with the flagella of sperm. In addition, VE1 reacts strongly with the cilia of the ependymal lining of the brain and with the cilia-containing microlumens of ependymoma tumors. There is significant sequence homology between the synthetic peptide (amino acid 596-606 of BRAF V600E: GLATEKSRWSG) that was used to generate the VE1 antibody and regions of multiple axonemal dynein heavy chain proteins (eg, DNAH2, DNAH7, and DNAH12). These proteins are major components of the axonemes of cilia and flagella where they drive the sliding of microtubules. In ELISA assays, we show that the VE1 antibody recognizes epitopes from these proteins. A familiarity with the cross-reactivity of the VE1 antibody with epitopes of proteins in cilia is of value when evaluating tissues stained with this important clinical antibody.

Rathke's cleft cysts with significant squamous metaplasia--high risk of postoperative deterioration and close origins to craniopharyngioma.

BACKGROUND: Rathke's cleft cyst (RCC) with significant squamous and/or stratified epithelium including smooth transition from single cuboidal to squamous epithelium (tRCC) is rare and possibly represents an intermediate form to craniopharyngioma. METHODS: Twelve patients with histologically confirmed tRCC were retrospectively investigated from a series of 167 cases of RCC and 96 cases of craniopharyngiomas. Clinical data were reviewed, and immunohistochemistry findings for cytokeratins and ß-catenin were examined. RESULTS: All lesions were located in the sella turcica with marked extension to suprasellar cistern. Six of the 12 patients had suffered postoperative re-enlargement, and three of these six patients required more than two additional operations and irradiation. CAM5.2 was positive in the glandular epithelium in all tRCCs and focally positive in the squamous epithelium of all these tRCCs. 34ßE12 was positive in the squamous epithelium in all tRCCs and focally positive in the glandular epithelium in all but one tRCC. The findings of cytokeratin expression of tRCCs were very similar to those of craniopharyngioma. ß-Catenin showed nuclear translocation in five cases. All patients with nuclear translocation of ß-catenin suffered postoperative re-enlargement. CONCLUSIONS: tRCC carries an extremely high risk of re-enlargement. Cytokeratin expression resembles that in craniopharyngioma, which might indicate a very close origin of these pathologies. Nuclear translocation of ß-catenin may be related to the aggressive clinical course.

Clinical application of intrathecal gadobutrol for assessment of cerebrospinal fluid tracer clearance to blood.

BACKGROUNDMethodology for estimation of cerebrospinal fluid (CSF) tracer clearance could have wide clinical application in predicting excretion of intrathecal drugs and metabolic solutes from brain metabolism and for diagnostic workup of CSF disturbances.METHODSThe MRI contrast agent gadobutrol (Gadovist) was used as a CSF tracer and injected into the lumbar CSF. Gadobutrol is contained outside blood vessels of the CNS and is eliminated along extravascular pathways, analogous to many CNS metabolites and intrathecal drugs. Tracer enrichment was verified and assessed in CSF by MRI at the level of the cisterna magna in parallel with obtaining blood samples through 48 hours.RESULTSIn a reference patient cohort (n = 29), both enrichment within CSF and blood coincided in time. Blood concentration profiles of gadobutrol through 48 hours varied between patients diagnosed with CSF leakage (n = 4), idiopathic normal pressure hydrocephalus dementia (n = 7), pineal cysts (n = 8), and idiopathic intracranial hypertension (n = 4).CONCLUSIONAssessment of CSF tracer clearance is clinically feasible and may provide a way to predict extravascular clearance of intrathecal drugs and endogenous metabolites from the CNS. The peak concentration in blood (at about 10 hours) was preceded by far peak tracer enhancement at MRI in extracranial lymphatic structures (at about 24 hours), as shown in previous studies, indicating a major role of the spinal canal in CSF clearance capacity.FUNDINGThe work was supported by the Department of Neurosurgery, Oslo University Hospital; the Norwegian Institute for Air Research; and the University of Oslo.

Optimized photochemistry enables efficient analysis of dynamic RNA structuromes and interactomes in genetic and infectious diseases.

Direct determination of RNA structures and interactions in living cells is critical for understanding their functions in normal physiology and disease states. Here, we present PARIS2, a dramatically improved method for RNA duplex determination in vivo with >4000-fold higher efficiency than previous methods. PARIS2 captures ribosome binding sites on mRNAs, reporting translation status on a transcriptome scale. Applying PARIS2 to the U8 snoRNA mutated in the neurological disorder LCC, we discover a network of dynamic RNA structures and interactions which are destabilized by patient mutations. We report the first whole genome structure of enterovirus D68, an RNA virus that causes polio-like symptoms, revealing highly dynamic conformations altered by antiviral drugs and different pathogenic strains. We also discover a replication-associated asymmetry on the (+) and (-) strands of the viral genome. This study establishes a powerful technology for efficient interrogation of the RNA structurome and interactome in human diseases.

Molecular pathogenesis of megalencephalic leukoencephalopathy with subcortical cysts: mutations in MLC1 cause folding defects.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare type of leukodystrophy, most often caused by mutations in the MLC1 gene. MLC1 is an oligomeric plasma membrane (PM) protein of unknown function expressed mainly in glial cells and neurons. Most disease-causing missense mutations dramatically reduced the total and PM MLC1 expression levels in Xenopus oocytes and mammalian cells. The impaired expression of the mutants was verified in primary cultures of rat astrocytes, as well as human monocytes, cell types that endogenously express MLC1, demonstrating the relevance of the tissue culture models. Using a combination of biochemical, pharmacological and imaging methods, we also demonstrated that increased endoplasmatic reticulum-associated degradation and endo-lysosomal-associated degradation can contribute to the cell surface expression defect of the mutants. Based on these results, we suggest that MLC1 mutations reduce protein levels in vivo. Since the expression defect of the mutants could be rescued by exposing the mutant-protein expressing cells to low temperature and glycerol, a chemical chaperone, we propose that MLC belongs to the class of conformational diseases. Therefore, we suggest the use of pharmacological strategies that improve MLC1 expression to treat MLC patients.

Reduction in Size of a Large Rathke's Cleft Cyst on Treatment with Low Dose of Corticosteroid.

Rathke's cleft cyst is a non-neoplastic sellar cyst, which is increasingly reported on radiological investigation performed for unrelated intra-cranial pathology. When symptomatic, it is associated with headache, visual symptoms, and pituitary dysfunction. We report a case of an 18 year-old male patient with Rathke's cleft cyst, who presented with failing vision, headache, and hypocortisolism. After defaulting on planned surgery, the patient continued to take a replacement dose of prednisolone for a year. He reported significant improvement in vision and remarkable reduction in cyst size on repeat imaging after a year. Surgery was later performed in view of persisting severe headache. The authors discuss the reduction in cyst size in relation to long-term usage of replacement steroid. They postulate that selected patients with Rathke's cleft cyst with radiological evidence of inflammatory fluid can be given a trial of glucocorticoids and assessed for cyst shrinkage and changes in imaging characteristics.

Rathke's cleft-like cysts arise from Isl1 deletion in murine pituitary progenitors.

The transcription factor ISL1 is expressed in pituitary gland stem cells and the thyrotrope and gonadotrope lineages. Pituitary-specific Isl1 deletion causes hypopituitarism with increased stem cell apoptosis, reduced differentiation of thyrotropes and gonadotropes, and reduced body size. Conditional Isl1 deletion causes development of multiple Rathke's cleft-like cysts, with 100% penetrance. Foxa1 and Foxj1 are abnormally expressed in the pituitary gland and associated with a ciliogenic gene-expression program in the cysts. We confirmed expression of FOXA1, FOXJ1, and stem cell markers in human Rathke's cleft cyst tissue, but not craniopharyngiomas, which suggests these transcription factors are useful, pathological markers for diagnosis of Rathke's cleft cysts. These studies support a model whereby expression of ISL1 in pituitary progenitors drives differentiation into thyrotropes and gonadotropes and without it, activation of FOXA1 and FOXJ1 permits development of an oral epithelial cell fate with mucinous cysts. This pituitary-specific Isl1 mouse knockout sheds light on the etiology of Rathke's cleft cysts and the role of ISL1 in normal pituitary development.

18F-FDG PET/CT in Labrune Syndrome.

A 69-year-old woman presented with cognitive impairment related to attentive, executive, and mnemonic functions; progressive worsening of walking, speaking, writing, and reading ability; and double sphincter incontinence. Leukoencephalopathy, cystic lesions, and calcifications, suspected for Labrune syndrome, were observed at MRI and CT brain images. Generalized wave abnormalities were also visible at electroencephalogram. Functional brain imaging performed with F-FDG PET/CT demonstrated a decreased glucose metabolism in impaired brain regions, in accordance with MRI findings. Genetic testing confirmed a mutation of SNORD118.

Cushing's Syndrome in a Patient With Rathke's Cleft Cyst and ACTH Cell Hyperplasia Detected by 11C-Methionine PET Imaging-A Case Presentation.

Background: Adrenocorticotropic Hormone (ACTH)-dependent Cushing's Syndrome (CS) is most often caused by a pituitary adenoma. Although rarely, it can also result from pituitary corticotroph cell hyperplasia (CH). Reports on concomitant pituitary lesions including ACTH-producing adenomas and Rathke's cleft cysts (RCCs) have been published. Positron emission tomography (PET), using 11C-labelled-methionine (MET) as a tracer and co-registered with magnetic resonance imaging (MRI) has been shown to be useful in the diagnosis of pituitary collision lesions, however, its role is still under investigation. In this work we present the case of a patient in whom CS was caused by non-adenomatous CH within the wall of an RCC. Case Summary: In 2015 a patient with signs and symptoms of CS was referred to our Department. Biochemical studies repeatedly showed elevated midnight serum cortisol and ACTH levels. Magnetic resonance imaging of the sellar region revealed an RCC and MET-PET/MR showed heterogeneous labelled-methionine metabolism in the vicinity of the cyst's wall. Transsphenoidal surgery resulted in rapid, complete and lasting relief of symptoms. Histopathological examination demonstrated an RCC and CH. Conclusions: Concomitance of pituitary focal lesions is a rare phenomenon. Methionine-labelled PET/MR may be useful in the diagnosis of collision sellar lesions, including CH. Corticotroph cell hyperplasia can present as mild and fluctuating hypercortisolaemia.

Late development of craniopharyngioma following surgery for Rathke's cleft cyst.

OBJECTIVE: Rathke's cleft cyst (RCC) may transform to papillary type craniopharyngioma (CP) after squamous metaplasia: this is referred to as ciliated CP. We encountered a case involving a patient who had late development of adamantinomatous CP following surgery for RCC, the details of which may shed light on the histogenesis of CP in general. PATIENT: A 41-year-old man presented to our institution with visual disturbance, and magnetic resonance imaging (MRI) showed a cystic mass in the suprasellar region. The patient underwent a biopsy via a transsphenoidal approach and was diagnosed as having a RCC. 34 months after the initial surgery, the patient revisited our hospital for a rapidly aggravating visual disturbance and underwent neuroendoscopic biopsy and tumor removal via a bifrontal craniotomy. Histologically, the tumor was shown to be an adamantinomatous CP. No nuclear beta-catenin accumulation was detectable in the previous RCC specimen, but nuclear beta-catenin accumulation was found in the recent CP specimen, restricted to whorl-like structures or surrounding ghost cells. CONCLUSIONS: Our case of adamantinomatous CP that developed long after removal of the RCC, diagnosed by beta-catenin staining, supports the hypothesis that CPs may develop from RCCs directly due to beta-catenin mutations. However, it still does not prove that a histogenetic connection can be shown between the two lesions which are clonally unrelated. Our case is reported as two consecutive lesions; this in itself is a rare situation.

Rethinking the stalk effect: a new hypothesis explaining suprasellar tumor-induced hyperprolactinemia.

The pars tuberalis is a distinct subdivision of the pituitary gland but its function remains poorly understood. Suprasellar tumors in this pars tuberalis region are frequently accompanied by hyperprolactinemia. As these tumors do not immunoreact for any of the established pituitary hormones, they are classified as nonsecretory. It has been postulated that these suprasellar tumors induce hyperprolactinemia by compressing the pituitary stalk, resulting in impaired dopamine delivery to the pituitary and, consequently, disinhibition of the lactotropes. An alternative hypothesis proposed is that suprasellar tumors secrete a specific pars tuberalis factor that stimulates prolactin secretion. Hypothesized candidates are the preprotachykinin A derived tachykinins, substance P and/or neurokinin A.

Interleukin-5 and interleukin-10 are produced in central nervous system tumor cysts.

Interleukin-5 and interleukin-10, as important mediators of vascular permeability, contribute to the development of various pathologic effusions. However, little is known regarding the involvement of these two cytokines in the formation of cysts associated with central nervous system (CNS) tumors. Twenty-eight patients with various cystic CNS tumors were investigated for expression of interleukin-5 and interleukin-10 in cyst fluid and their matched cytokine receptors in tumor tissue. Interleukin-5 and interleukin-10 were detected in cyst fluid, and interleukin-5 concentration was significantly correlated with interleukin-10 concentration (r=0.508, p=0.006). Moreover, both receptors were also detectable in the tumor tissue specimens and high levels of expression were also found in perivascular cells. Therefore, the local production of interleukin-5 and interleukin-10 might be implicated in some types of cyst formation.

Pituitary function after endonasal surgery for nonadenomatous parasellar tumors: Rathke's cleft cysts, craniopharyngiomas, and meningiomas.

BACKGROUND: Transsphenoidal surgery for parasellar nonadenomatous lesions has the possibility to either improve or worsen pituitary hormonal function. Herein we present the rates and risk factors of new hormonal failure and recovery in patients undergoing surgery for either an RCC, craniopharyngioma, or tuberculum sella meningioma. METHODS: All consecutive patients treated over an 8-year period by endonasal surgery for an RCC, craniopharyngioma, or tuberculum sella meningioma were analyzed. Patients treated with prior sellar radiotherapy were excluded. Preoperative and postoperative pituitary hormonal status was determined. Patient characteristics, tumor size, intraoperative and postoperative events, and extent of tumor resection were correlated with new or resolved hypopituitarism. RESULTS: In total, 50 patients with an RCC, 18 with a craniopharyngioma and 13 with tuberculum sellae meningioma, were analyzed. New anterior pituitary failure and permanent DI occurred as follows: in RCCs, 6% and 2%; in craniopharyngiomas, 31% and 39%; and in meningiomas, 9% and 0%. Overall, improved hormonal function occurred in 57% of patients with an RCC including recovery of one or more anterior axes in 9 (41%) of 22 patients and resolution of hyperprolactinemia in 12 (67%) of 18 patients; no patients with a craniopharyngioma or meningioma had resolution of hypopituitarism. Younger age was predictive of hormonal recovery in patients with an RCC (P = .026). CONCLUSIONS: New hypopituitarism after transsphenoidal surgery occurs in approximately one third of patients with a craniopharyngioma and in less than 10% of patients with an RCC or suprasellar meningioma. Hormonal function improves in the majority of patients undergoing drainage of an RCC but is unlikely to occur after removal of a craniopharyngioma or suprasellar meningioma.

Comparative immunohistochemical assessment of craniopharyngioma and related lesions.

Craniopharyngiomas (CP), Rathke's cleft cysts (RCC), and sellar xanthogranulomas (XG) are closely related lesions. As expression of cytokeratins 8 (CK8) and 20 (CK20) was reported in RCC but not in CP, the present study investigates the reproducibility of immunohistochemical distinction between CP and RCC, attempting to identify the relationship of XG to these lesions. A comparative study of 55 patient specimens (25 CP, 28 RCC, and 2 XG) was analyzed for the histological features of xanthomatous changes and squamous metaplasia, and expression of CK8 and CK20. In the 25 CP cases, xanthomatous changes were seen in 5 (20%), with CK8 reactivity demonstrated in all 25 cases. A prominent xanthomatous component was identified in 13 of 28 RCC (46%), and squamous metaplasia was seen in 11 (39%), 9 of which also contained xanthomatous features. CK8 reactivity was demonstrated in all 28 RCC cases, whereas CK20 was seen only in 9 cases (32%). Of the two cases diagnosed as XG, none contained epithelium, and immunohistochemistry for cytokeratins was not observed. Overall, differential expression of cytokeratins cannot reliably distinguish CP from RCC. Furthermore, expression of CK20 in RCC is generally seen within a background of prominent squamous metaplasia and reactive xanthomatous changes.

Clinicopathological and endocrinological study of Rathke's cleft cyst manifesting as hyponatremia.

Rathke's cleft cyst becomes symptomatic in a few cases. Increasing experience has identified previously unrecognized clinical effects including pituitary dysfunction. This study retrospectively investigated eight patients with Rathke's cleft cyst manifesting as hyponatremia and treated surgically with histological confirmation to clarify the mechanism of hyponatremia. All patients suffered from physical symptoms caused by the hyponatremia. All patients underwent magnetic resonance (MR) imaging and screening of pituitary hormones in addition to cortisol and thyroid hormones. All patients had cysts of more than 10 mm in diameter and MR imaging frequently showed irregularly thickened cyst wall. Histological examination disclosed various phases of inflammation and significant fibrosis. Endocrinological examination showed low concentrations of both serum cortisol in all eight patients and urinary cortisol in six of six patients examined. The major cause of hyponatremia was hypocortisolemia, induced by damage to the anterior pituitary gland.

Discovery of Aquaporin-1 and Aquaporin-4 Expression in an Intramedullary Spinal Cord Ependymal Cyst: Case Report.

BACKGROUND: Intramedullary ependymal cysts of the spinal cord are rare, benign, fluid-filled cysts usually situated along the ventral surface of the spinal cord. Only 32 cases have been reported since they were first described. Thus, owing to the rarity at which these cysts are encountered, their management and pathogenesis remain controversial. Whereas some investigators have advocated for cystosubarachnoid shunt placement for symptomatic ependymal cysts, others have argued for complete cyst resection or simple fenestration. Here we report the case of a 56-year-old female with a T11-T12 ependymal cyst that was successfully managed with cyst fenestration. We further investigated a potential pathological mechanism of cyst formation by performing immunohistochemistry to detect aquaporin expression in the cyst lining. CASE DESCRIPTION: A 56-year-old female was found to harbor an enlarging cystic lesion of the conus that was discovered on workup of progressive paraparesis and urinary incontinence. She had lower extremity weakness and progressive myelopathy. Thoracic laminectomy with cyst fenestration arrested her neurologic deterioration. Pathological analysis revealed an intramedullary ependymal cyst. Immunohistochemistry was subsequently performed for expression of aquaporin-1 and aquaporin-4. There was dense staining of the underlying neuropil with concurrent membranous staining pattern of the cyst lining. CONCLUSIONS: Intramedullary ependymal cysts are rare, cystic lesions of the spinal cord. Early cyst fenestration decompresses the cyst and prevents neurologic deterioration. Here we report for the first time that aquaporins are expressed in the cyst wall, which is consistent with a passive, osmotic pathogenic mechanism of cyst formation.

Nuclear beta-catenin accumulation as reliable marker for the differentiation between cystic craniopharyngiomas and rathke cleft cysts: a clinico-pathologic approach.

Clinical and histopathologic differentiation of cystic lesions from the sellar region, that is, craniopharyngiomas (CPs) and Rathke cleft cysts (RCCs), is challenging and has paramount importance with respect to variable clinical manifestation and adapted surgical treatment strategies in both entities. Here, we retrospectively evaluated clinico-pathologic findings in 81 patients presenting with a cystic tumor located in the sellar region. All patients underwent transsphenoidal or transcranial resections. Microscopic inspection of surgical specimens identified CP in 51 patients, and RCC in 30 patients. Amongst the panel of immunohistochemical marker proteins used for histopathologic analysis, nuclear accumulation of beta-catenin was detectable only in CP. On the basis of the histopathologic and immunohistochemical analysis, clinical presentation (sex, age, ophthalmologic, and endocrinologic deficits), imaging (tumor location, size, and calcification), as well as a description of cyst contents obtained during operation were retrospectively evaluated. In purely cystic CPs, an isointense signal was more frequent in T1-weighted magnetic resonance images and calcification of the tumor capsule in computed tomography scans. In addition, the size of RCC was smaller and this tumor entity was more often located within the sella. Aberrant (nuclear) immunohistochemical staining for beta-catenin appeared, however, as most reliable factor for the differentiation between purely cystic CPs and RCCs, whereas tumor location, tumor size, and calcification of the tumor capsule were less consistent parameters. The data are compatible with distinct pathogenic pathways associated with these related histopathologic entities.

Leukoencephalopathy with bilateral anterior temporal lobe cysts.

Recently, several reports describing patients with a nonprogressive clinical course, increased signal in the cerebral white matter, and cystic changes in the anterior temporal lobes on magnetic resonance imaging (MRI) have appeared. To date, 25 patients with this very distinctive condition have been described. We report four new cases of this newly recognized entity. All have been identified primarily because of the distinctive MRI features consisting of the very unusual anterior temporal lobe cystic changes. The clinical features are characterized by severe, disabling, but nonprogressive mental and motor retardation. Magnetic resonance spectroscopy has shown increased myo-inositol and decreased N-acetylaspartate in the cerebral white matter. This is a distinctive, probably genetic, condition with characteristic neuroimaging and clinical features. In the appropriate clinical situation, the neuroimaging features are diagnostic.

TREM-1 expression in craniopharyngioma and Rathke's cleft cyst: its possible implication for controversial pathology.

Whether a mixed type of craniopharyngioma (CP) exists and whether papillary craniopharyngioma (pCP) is on a histopathological continuum with Rathke's cleft cyst (RCC) remain controversial. Herein, we examined the expression and localization of ß-catenin, BRAF p.V600E (V600E), and triggering receptor expressed on myeloid cells-1 (TREM-1) in 58 samples including 20 pCPs, 26 adamantinomatous craniopharyngiomas (aCP), and 12 RCCs. Five aCPs were diagnosed with mixed type CPs and the remaining 21 cases were pure aCPs. Four of the 12 RCCs presented with significant squamous epithelium (SE). V600E immunoreactivity was observed in all pCPs in the cytoplasm, but not in the nuclei. aCPs and RCCs, including mixed type CP, did not express V600E. Nuclear ß-catenin translocation was detected exclusively in aCPs. TREM-1 was expressed in pCPs. Additionally, TREM-1 expression was detected in the SE of 5 "mixed type" CPs, while it was absent in pure aCPs. TREM-1 was expressed in 4 RCCs with SE, but not in the remaining 8 RCCs. TREM-1 mRNA levels were compared in cultured pCP and aCP cells. TREM-1 mRNA level was significantly (p < 0.001; up to 4.045 fold) higher in pCPs than in aCPs. Western blotting revealed a significantly (p < 0.001; up to 7.19 fold) lower level of TREM-1 expression in aCP cells compared to that in pCP cells. Our findings further supported that RCC and pCP may represent two ends of a morphological spectrum. A variant showing overlapping histological features of aCP and pCP should not be considered as a mixed type.