Overexpression of helper T cell type 2-related molecules in the skin of patients with eosinophilic dermatosis of hematologic malignancy.

BACKGROUND: Eosinophilic dermatosis of hematologic malignancy (EDHM) is a rare dermatosis associated with blood tumors. OBJECTIVE: To characterize the expression of T-cell and B-cell markers and pruritogenic mediators in EDHM skin. METHODS: Immunohistochemical and immunofluorescence analysis were performed in 12 skin samples of EDHM, 11 samples of bullous pemphigoid (BP), and 5 samples from healthy controls (HC). Serum levels of interleukin (IL) 4 were analyzed in 11 patients with EDHM, 11 BP patients, and 5 HC by enzyme-linked immunosorbent assay. RESULTS: T-cell markers, including clusters of differentiation (CD) 3, CD4, CD8, and CD5 were significantly overexpressed in EDHM and BP skin compared to HC. A predominance of CD4+ over CD8+ cells and GATA3+ (helper T cell type 2 [Th2] marker) over T-bet+ (Th1 marker) cells were observed. FOXP3 expression was increased but the FOXP3/CD4 ratio was low. B-cell markers were under-represented, without significant differences between the 3 groups. IL-4 and IL-31 were significantly overexpressed in EDHM and BP compared to HC and colocalized with the Th2-associated marker GATA3. Eotaxin-1 was significantly overexpressed in EDHM compared to BP and HC. IL-4 serum concentration was significantly increased in EDHM and BP compared to HC. LIMITATIONS: Small sample size; retrospective design. CONCLUSIONS: Targeting Th2-related molecules, in particular IL-4, holds promise for EDHM management.

Ataxia-Telangiectasia Mutated Loss of Heterozygosity in Melanoma.

ATM germline pathogenic variants were recently found enriched in high-risk melanoma patients. However, ATM loss of heterozygosity (LOH) has never been investigated in melanoma and, therefore, a causal association with melanoma development has not been established yet. The purpose of this study was to functionally characterize 13 germline ATM variants found in high-risk melanoma patients-and classified by in silico tools as pathogenic, uncertain significance, or benign-using multiple assays evaluating ATM/pATM expression and/or LOH in melanoma tissues and cell lines. We assessed ATM status by Immunohistochemistry (IHC), Western Blot, Whole-Exome Sequencing/Copy Number Variation analysis, and RNA sequencing, supported by Sanger sequencing and microsatellite analyses. For most variants, IHC results matched those obtained with in silico classification and LOH analysis. Two pathogenic variants (p.Ser1135_Lys1192del and p.Ser1993ArgfsTer23) showed LOH and complete loss of ATM activation in melanoma. Two variants of unknown significance (p.Asn358Ile and p.Asn796His) showed reduced expression and LOH, suggestive of a deleterious effect. This study, showing a classic two-hit scenario in a well-known tumor suppressor gene, supports the inclusion of melanoma in the ATM-related cancer spectrum.

Dysembryoplastic neuroepithelial tumors: A single-institutional series with special reference to glutamine synthetase expression.

Dysembryoplastic neuroepithelial tumors (DNT) is a benign (World Health Organisation, WHO, grade I) glioneuronal tumor and it represent one of the most frequent neoplasm in patient affected by seizures. The epileptic neuronal activity can be determined by abnormal synchronization, excessive glutamate excitation and\or inadequate GABA inhibition. Increasing evidence suggests that the astrocytes might be involved in this process even if neurons play a relevant role. In particular astrocytes promote the clearance of glutamate, a potent excitatory neurotransmitter of the central nervous system. Indeed, elevated concentrations of extracellular glutamate may determine iper-excitability and seizures as well as other neurological disorders. So, astrocytes, converting glutamate into glutamine via the enzyme glutamine synthetase (GS), could play a protective anti-seizures role. In the present study, we analyzed the immunohistochemical expression of GS in 20 DNTs specimens documenting a constant immunoistochemical expression of GS in astrocytes of the lesional tissue and of the cerebral cortex.

Canine Clitoral Carcinoma: A Clinical, Cytologic, Histopathologic, Immunohistochemical, and Ultrastructural Study.

Vaginal and vulvar tumors are uncommon in dogs. Knowledge of canine primary clitoral neoplasia is restricted to a few case reports, and only carcinomas have been reported. Cytologic and histologic features reported in the literature seem to overlap with those of canine apocrine gland anal sac adenocarcinoma (AGASA). Clinical features also recall those of canine AGASA, such as locoregional metastases and hypercalcemia of malignancy (HM). In this study, 6 cases of primary canine clitoral carcinomas (CCCs), with and without HM, were investigated by means of cytology, histopathology, electron microscopy, and immunohistochemistry for neuroendocrine markers including chromogranin A (CGA), synaptophysin (SYN), neuron-specific enolase (NSE), and S-100. In all 6 tumors, cytologic findings were consistent with malignant epithelial neoplasia of apocrine gland origin. The tumors examined were classified into 3 different histological patterns representing different degrees of differentiation: tubular, solid, and rosette type. Both CGA and SYN were mildly expressed in 2 of 6 tumors, while NSE was consistently expressed in all 6 cases. None of the tumors were S-100 positive. Transmission electron microscopy revealed electron-dense cytoplasmic granules compatible with neuroendocrine granules in all 6 cases. CCCs presented clinicopathologic features resembling AGASAs with neuroendocrine characteristics, and 2 of 6 neoplasms were considered as carcinomas with neuroendocrine differentiation and were positive for 3 neuroendocrine markers. CCCs can often present with HM, and long-term outcome is likely poor. Our study concludes that CCC seems to be a rare tumor, but it might be underestimated because of the overlapping features with AGASA. Further studies should aim to define the true incidence of this disease.

Pituitary adenoma with adipose tissue: A new metaplastic variant.

Pituitary adenomas are benign tumors representing approximately 15-20% of intracranial neoplasms. There have been few reports of metaplastic osseous transformation and about 60 cases of neuronal metaplasia in pituitary adenoma but adipose metaplasia has not been previously described in the English literature. Here we report a case of pituitary adenoma with metaplastic adipose tissue in a 58-year-old male patient. Histologically this case fulfilled the criteria of a non-functioning pituitary adenoma, and moreover a central area of adipose tissue, made by mature adipocytes, and many tumor cells, containing fat droplet were evident. Lipomatous transformation of tumor cells in the CNS has been previously observed but, to the best of our knowledge, our case is the first pituitary adenoma with such change. The histogenesis of the adipose element in pituitary adenoma is not well understood, and could be a result of a metaplastic change or divergent differentiation from a common progenitor cell.

Subependymal giant cell astrocytoma: a lesion with activated mTOR pathway and constant expression of glutamine synthetase.

Subependymal giant-cell astrocytoma (SEGA) is a rare tumor associated with tuberous sclerosis complex (TSC). TSC mainly involves the central nervous system (CNS) where SEGA, subependymal nodules, and cortical tubers may be present. First studies suggested the astrocytic nature of SEGA while successive studies demonstrated the mixed glio-neuronal nature. There are similarities between TSC-associated CNS lesions and type IIb focal cortical dysplasia (FCD). In all these pathologies, mammalian target of rapamycin (mTOR) pathway activation has been demonstrated. Recent data evidenced that balloon cells in FCD IIb express glutamine synthetase (GS). GS is involved in the clearance of glutamate. Cells expressing GS might exert an antiepileptic role. We evaluated by immunohistochemistry the glial fibrillary acidic protein (GFAP), neurofilaments (NF), and GS expression and the mTOR status (mTOR and phosphorylated ribosomal protein S6) in 16 SEGAs and 2 cortical tubers. Our purpose was to emphasize the mixed nature of SEGA and to further investigate the similarities between TSC-related CNS lesions (in particular SEGA) and FCD IIb. We confirm the glio-neuronal nature and the common activation of the mTOR pathway in SEGAs. In addition, we report for the first time that these tumors, analogously to FCD IIb, commonly express GS. Notably, the expression of mTOR, phosphorylated ribosomal protein S6, and GS was restricted to gemistocytic-like GFAP-negative cells. GS expression and mTOR pathway activation were also documented in cortical tubers. Further studies are necessary to understand the significance of GS expression in SEGAs as well as in cortical tubers.

Immunohistochemistry is highly sensitive and specific for the detection of NRASQ61R mutation in melanoma.

Testing for NRAS is now integral part in the assessment of metastatic melanoma patients because there is evidence that NRAS-mutated patients may be sensitive to MEK inhibitors, and RAS mutation is a common mechanism of acquired resistance during treatment with BRAF inhibitors. This study evaluated the sensitivity and specificity of immunohistochemical analysis using an N-Ras (Q61R) antibody to detect the presence of the NRASQ61R mutation in melanoma patients. A total of 98 primary cutaneous melanomas that have undergone examination of NRAS mutation were retrieved from a multicentric database. Formalin-fixed and paraffin-embedded melanoma tissues were analyzed for BRAF and NRAS mutations by independent, blinded observers using both conventional DNA molecular techniques and immunohistochemistry with the novel anti-human N-Ras (Q61R) monoclonal antibody (clone SP174). The antibody showed a sensitivity of 100% (14/14) and a specificity of 100% (83/83) for detecting the presence of an NRASQ61R mutation. Of the NRAS-mutated cases, none of the non-Q61R cases stained positive with the antibody (0/7). There were three cases with discordant NRAS mutational results. Additional molecular analysis confirmed the immunohistochemically obtained NRAS result in all cases, suggesting that a multiple analytical approach can be required to reach the correct sample classification. The reported immunohistochemical method is an accurate, rapid, and cost-effective method for detecting NRASQ61R mutation in melanoma patients, and represents a valuable supplement to traditional mutation testing. If validated in further studies, genetic testing would only be required for immunohistochemistry-negative patients to detect non-Q61R mutations.

Expression of glutamine synthetase in balloon cells: a basis of their antiepileptic role?

Glutamine synthetase is an enzyme involved in the clearance of glutamate, the most potent excitatory neurotransmitter. We studied the immunohistochemical expression of glutamine synthetase in neocortical samples from 5 children who underwent surgery for pharmacoresistant epilepsy and a histological diagnosis of focal cortical dysplasia IIb. In all cases, balloon cells, but not dysmorphic neurons, were immunopositive for glutamine synthetase. This finding suggests that balloon cells can be involved in the neutralization of glutamate and play a protective anti-seizure role.

ß-adrenoceptors are upregulated in human melanoma and their activation releases pro-tumorigenic cytokines and metalloproteases in melanoma cell lines.

Recent studies sight ß-adrenergic receptor (AR) antagonists as novel therapeutic agents for melanoma, as they may reduce disease progression. Here within, we evaluated the expression of ß-ARs in a series of human cutaneous melanocytic lesions, and studied the effect of their endogenous agonists, norepinephrine (NE) and epinephrine (E), on primary and metastatic human melanoma cell lines. Using immunohistochemistry, we found that both ß1- and ß2-ARs are expressed in tissues from benign melanocytic naevi, atypical naevi and malignant melanomas and that expression was significantly higher in malignant tumours. Melanoma cell lines (human A375 primary melanoma cell line and human Hs29-4T metastatic melanoma cell lines) also expressed ß1- and ß2-ARs by measuring transcripts and proteins. NE or E increased metalloprotease-dependent motility, released interleukin-6 and 8 (IL-6, IL-8) and vascular endothelial growth factor (VEGF). These effects of catecholamines were inhibited by the unselective ß-AR antagonist propranolol. The role of soluble factors elicited by catecholamines seemed pleiotropic as VEGF synergized with NE increased melanoma invasiveness through 3D barriers, while IL-6 participated in stromal fibroblast activation towards a myofibroblastic phenotype. Our results indicate that NE and E produce in vitro via ß-ARs activation a number of biological responses that may exert a pro-tumorigenic effect in melanoma cell lines. The observation that ß-ARs are upregulated in malignant melanoma tissues support the hypothesis that circulating catecholamines NE and E, by activating their receptors, favour melanoma progression in vivo.

Differential HLA class I subunit (A, B, C heavy chain and ß2-microglobulin) expression levels in normal tissues.

Human leukocyte antigen (HLA) class I subunit expression level in primary and metastatic lesions has been characterized in many cancer types utilizing formalin-fixed and paraffin-embedded (FFPE) tissue sections as substrates in immunohistochemical reactions. The evaluation of the results of these studies has been hampered by the scant information about HLA class I subunit expression level in normal tissues. To address this unmet need, we have analyzed the HLA class I subunit expression level in FFPE sections of normal tissues.Two tissue microarray (TMA) blocks were constructed from archived FFPE tissue samples of a wide number of human normal tissues. The expression level of HLA-A, HLA-B, HLA-C heavy chains and ß2-microglobulin (ß2-M) was evaluated by IHC staining, with mAb HC-A2, mAb HC-10, and mAb NAMB1, respectively. The staining was scored according to its intensity.According to their staining patterns with the three mAbs tested, normal tissues can be divided into four groups: (i) tissues displaying moderate/strong staining patterns, (ii) tissues displaying barely detectable staining patterns, (iii) tissues displaying differential staining patterns, and (iv) tissues with no detectable staining. The ubiquitous expression pattern for HLA-A, B, C heavy chain and ß2-M was found only at the endothelial level; the stroma was negative except for fibroblasts in all the tissues analyzed. Our data suggest that, contrary to the general postulate, HLA class I subunit expression is not detectable in all nucleated cells. This information provides a useful background to evaluate changes in HLA class I subunit expression associated with the malignant transformation of cells.

A Fast and Automated Melanin-bleaching Method for Histopathologic Evaluation of Pigmented Melanoma Tissues.

Histopathologic examination of highly pigmented melanoma tissues has always been a challenge for pathologists. The high concentration of melanin pigment is an obstacle for immunohistochemistry and the ensuing evaluation. Therefore, removing melanin has become a crucial step for processing heavily pigmented melanoma samples. Several bleaching techniques have been proposed in the past, however, the most commonly used methods are time-consuming and poorly standardized. In this study, we propose a new fast and fully automated bleaching method applicable to validated immunohistochemical panels already used in the diagnosis of melanocytic tumors. The proposed bleaching protocol is based on sample pretreatment with 0.5% hydrogen peroxide and a Tris base pH 10 solution for 8 minutes at 80°C before antigen retrieval. Immunohistochemistry with HMB45, MART-1, Ki-67, SOX10, S-100, Tyrosinase, and BRAF(V600E) antibodies showed that this pretreatment removed excess melanin without affecting the tissue antigenicity and cytoarchitecture. In conclusion, we propose a new fast and automated bleaching protocol, easily transferable to a routine setting with efficient results in specimens in which the melanin pigmentation could blunt the histopathologic examination.

Bright-Field Multiplex Immunohistochemistry Assay for Tumor Microenvironment Evaluation in Melanoma Tissues.

The tumor microenvironment (TME) plays a crucial role in melanoma development, progression and response to treatment. As many of the most relevant TME cell phenotypes are defined by the simultaneous detection of more than two markers, the bright-field (BF) multiplex immunohistochemistry (IHC) technique has been introduced for the quantitative assessment and evaluation of the relative spatial distances between immune cells and melanoma cells. In the current study, we aimed to validate BF multiplex IHC techniques in the Ventana Discovery Ultra Immunostainer to be applied to the evaluation of the TME in variably pigmented melanoma tissues. The BF multiplex IHC staining was performed using different combinations of six immune-cell markers-CD3, CD4, CD8, CD20, CD68 and CD163-and the melanoma cell marker SOX10. Our results show that the BF double IHC Yellow/Purple protocol guarantees the maximum contrast in all the cell populations tested and the combination SOX10 (Green), CD8 (Yellow) and CD163 (Purple) of the BF triple IHC protocol ensures the best contrast and discrimination between the three stained cell populations. Furthermore, the labeled cells were clearly distinct and easily identifiable using the image analysis software. Our standardized BF IHC multiplex protocols can be used to better assess the immune contexts of melanoma patients with potential applications to drive therapeutic decisions within clinical trials.

Primary cerebral myxofibrosarcoma: clinical, morphologic, immunohistochemical, molecular, and ultrastructural study of an infrequent tumor in an extraordinary localization.

Herein, we describe an intracerebral primary low-grade myxofibrosarcoma occurring in a 9-year-old boy. The lesion measured 7 cm and occupied the left parieto-occipital region. A gross-total removal of the tumor was performed. Nine months later, radiologic follow-up revealed a local recurrence which was again surgically removed. The patient then underwent radiotherapy and chemotherapy. He was well and disease-free at 6 months follow-up. The tumor was composed of spindle, stellated, and multinucleated cells embedded in a myxoid background. Foci of increased cellularity, pleomorphism, and high mitotic rate were present. The tumor borders were sharply demarcated from the non-neoplastic nervous parenchyma. Immunohistochemical staining showed that the neoplastic cells were vimentine and CD34 positive. Fluorescence in-situ hybridization analyses did not show FUS and EWSR1 gene rearrangements. Primary intracranial myxofibrosarcomas are very rare (to the best of our knowledge, less than 10 published cases in the international literature). We believe each new case should be recorded to produce a better clinical, pathologic, molecular, prognostic, and therapeutic characterization of this lesion.

Mammary carcinoma in a tiger (Panthera tigris): morphological and immunohistochemical study.

The histologic and immunohistochemical features of a case of mammary gland carcinoma are described in a 14-yr-old female tiger (Panthera tigris). Immunoreactivity to estrogen receptor (ER), progesterone receptor (PR), tumoral protein 53 (p53), vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER-2), and cyclooxigenase-2 (COX-2) was investigated. Neoplastic cells were negative for ER, PR, and p53 but showed positivity for VEGF, HER-2, and COX-2, both in the primary and the metastatic lesions. Histopathologic findings and immunohistochemistry results suggested that the malignant behavior of the reported case could be comparable with some aggressive cat mammary carcinomas.

PreImplantation Factor immunohistochemical expression correlates with prostate cancer aggressiveness.

BACKGROUND: The PreImplantation Factor (PIF)-a peptide secreted by viable embryos-exerts autotrophic protective effects, promotes endometrial receptivity and controls trophoblast invasion. Synthetic PIF (sPIF) has both immune-protective and regenerative properties, and reduces oxidative stress and protein misfolding. PIF is detected by immunohistochemistry (IHC) in hyperplastic endometriotic lesions and advanced uterine cancer. sPIF reduces graft-versus-host disease while maintaining a graft-versus-leukemia effect. METHODS: PIF detection in prostate cancer was assessed in 50 human prostate samples following radical prostatectomy using tumor-microarray-based IHC correlating PIF immune staining with Gleason score (GS) and cancer aggressiveness. RESULTS: PIF was detected in moderate-to-high risk prostate cancer (GS 4+3 and beyond, prognostic groups 3 to 5). In prostate cancer (GS (WHO Grade Group (GG)5), PIF was detected in 50% of cases; in prostate cancer (GS 4+4 GG4), PIF was observed in 62.5% of cases; in prostate cancer (GS 4+3 GG3), PIF immunostaining was observed in 57.1% of cases. In prostate cancer, (GS 3+4 GG2) and (GS 3+3 GG1) cases where PIF staining was negative to weak, membranous staining was observed in 20% of cases (staining pattern considered negative). High-grade prostate intraepithelial neoplasia PIF positive stain in 28.57% of cases (6 of 21) was observed. In contrast, PIF was not detected in normal prostate glands. Importantly, sPIF added to the PC3 cell line alone or combined with prostate cancer fibroblast feeder-cells did not affect proliferation. Only when peripheral blood mononuclear cells were added to the culture, a minor increase in cell proliferation was noted, reflecting local proliferation control. CONCLUSIONS: Collectively, PIF assessment could be a valuable, simple-to-use immunohistochemical biomarker to evaluate aggressiveness/prognosis in specimens from prostate cancer patients.

Correction to: PD-L1 expression in bladder primary in situ urothelial carcinoma: evaluation in BCG-unresponsive patients and BCG responders.

This correction is being done to update the right surname of first name of authors of this manuscript. This does not change the results or the views presented in this manuscript.

PD-L1 expression in bladder primary in situ urothelial carcinoma: evaluation in BCG-unresponsive patients and BCG responders.

Carcinoma in situ (CIS) is believed to be a precursor of muscle-invasive carcinomas that may arise from these flat high-grade, superficial urothelial lesions. CIS accounts for approximately 10% of all bladder tumors. Therapeutic options for urothelial CIS are limited, and in order to inhibit disease progression and recurrence, current guidelines recommend transurethral resection (TURBT) followed by intravesical administration of Bacillus of Calmette-Guerin (BCG). Approximately 30-40% of patients fail the BCG therapy with recurrence and progression of disease. In the present study, we examined the expression of PD-L1 both in neoplastic epithelial cells and in stromal inflammatory cells in patients with diagnosis of CIS primary responders and not responders to BCG therapy, in order to verify if the PD-L1 expression could identify patients resistant to BCG treatment. Moreover, we analyzed on the same cases the immunoreactivities of anti-PD-L1 MoAbs such as SP263, C23, and SP142. Our results have showed that PD-L1 expression in tumor cells and in immune cell compartment is higher in BCG-unresponsive group than in BCG responders, but only the PD-L1 22C3 expression in tumor cells seems to be associated with recurrence of disease (p = 0.035; OR 0.1204; CI 95% from 0.0147 to 1.023). Hence, our data suggest that the PD-L1 22C3 expression could help to identify CIS that fail the BCG therapy, supporting the hypothesis that enhanced levels of intratumoral PD-L1 22C3 expressed by the tumor cells may explain the failure of BCG immunotherapy.

Increase in FOXP3+ regulatory T cells in GVHD skin biopsies is associated with lower disease severity and treatment response.

In animal models, CD4+/CD25+ T-regulatory cells (Tregs) have been reported to prevent/delay the onset of graft-versus-host disease (GVHD). Recently, an insufficient upregulation of Tregs was found in target organ (intestinal) biopsies from patients with GVHD. We have analyzed by immunohistochemistry the number of CD3+ T lymphocytes and FOXP3+ Tregs in skin biopsies from (1) recipients of allogeneic hematopoietic stem cell transplantation (HSCT, n = 26), (2) nontransplanted patients diagnosed with cutaneous drug reaction (n = 12), and (3) healthy donors (n = 10). Infiltrating CD3+ cells were significantly higher in both transplanted patients showing acute GVHD (aGVHD) and drug reaction when compared to healthy donors and patients without GVHD. Tregs number in aGVHD was higher than in patients without GVHD or healthy subjects and lower than in drug reaction. Interestingly, the number of infiltrating FOXP3+ Tregs was significantly higher in patients responding to GVHD treatment and with a low GVHD grade. Increase in FOXP3+ Tregs in GVHD skin biopsies correlates with less severe GVHD and is associated with response to GVHD treatment. Larger studies are required to confirm that evaluation of Tregs in minimally invasive skin biopsies assists the diagnosis and prognosis of GVHD patients.

Inducible nitric oxide synthase expression in melanoma: implications in lymphangiogenesis.

Cutaneous melanoma preferentially metastasizes via the lymphatic route. However, the mechanisms of lymphatic invasion and metastasis to regional lymph nodes are poorly understood. Nitric oxide is a free radical molecule synthesized from L-arginine by nitric oxide synthases that plays a critical role in various physiological and pathological processes, including tumor growth and angiogenesis. We have tested whether inducible nitric oxide synthase expression correlates with lymphatic vessel density identified with D2-40 antibody and/or blood microvessel density identified with CD105/endoglin in a series of melanocytic nevi (n=28) and cutaneous melanomas (n=38), representative of various pT. Inducible nitric oxide synthase expression was significantly lower in melanocytic nevi in comparison with primary and metastatic melanomas (P<0.001). Mean microvessel density was significantly higher in primary and metastatic melanomas in comparison with melanocytic nevi (P<0.001 for intratumoral and P=0.001 for peritumoral vessels). Vertical growth phase melanomas showed a higher intratumoral microvessel density in comparison with radial growth phase melanomas (P=0.02). The number of peritumoral lymphatics was significantly lower in nevi as compared with primary and metastatic melanomas (P=0.01). No correlation between microvessel or lymphatic vessel and clinical outcome was found in melanomas. A significant direct correlation was observed between inducible nitric oxide synthase immunostaining in melanocytic tumor cells and the density of lymphatic vessels (peritumoral: P=0.001; intratumoral: P=0.08), and the density of peritumoral blood microvessel (P=0.02). Our findings support the hypothesis that inducible nitric oxide synthase is implicated not only in blood, but also in lymphatic vascular neoformation in melanoma. Mechanistic studies are needed to address the possibility that inducible nitric oxide synthase controls lymphangiogenesis, dissemination and lymphatic borne metastases.

A Diagnostic Pitfall: Atypical Teratoid Rhabdoid Tumor Versus Dedifferentiated/Poorly Differentiated Chordoma: Analysis of a Mono-institutional Series.

Atypical teratoid/rhabdoid tumor (AT/RT) and dedifferentiated/poorly differentiated chordoma are pediatric tumors with some overlapping morphologic, immunohistochemical, and molecular features. Both these tumors have alterations in the tumor suppressor gene SMARCB1 resulting in loss of expression of the INI-1 protein. On the contrary, dedifferentiated/poorly differentiated chordoma expresses the transcription factor brachyury, whereas AT/RT does not. In this article we have reviewed the clinicopathologic features of a pediatric series of tumors (17 samples from 14 patients) located in the brain or within the axial spine and the base of the skull diagnosed as AT/RTs or as dedifferentiated/poorly differentiated chordomas. On the basis of the INI-1 and brachyury immunohistochemical results we reevaluated the initial diagnoses. Four misdiagnoses were revised. The differential diagnosis between AT/RT and dedifferentiated/poorly differentiated chordoma or on occasion medulloblastoma may be difficult. The use of 2 antibodies, INI-1, and brachyury, may be the key for the right diagnosis.