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Standardized treatment options are lacking for patients with unresectable or multifocal follicular dendritic cell sarcoma (FDCS) and disease-related mortality is as high as 20%. Applying whole-genome sequencing (WGS) in one case and whole-exome sequencing (WES) in additional twelve cases, this study adds information on the molecular landscape of FDCS, expanding knowledge on pathobiological mechanisms and identifying novel markers of potential theragnostic significance. Massive parallel sequencing showed high frequency of mutations on oncosuppressor genes, particularly in RB1, CARS and BRCA2 and unveiled alterations on homologous recombination DNA damage repair-related genes in 70% (9/13) of cases. This indicates that patients with high-stage FDCS may be eligible for poly ADP ribose polymerase inhibition protocols. Low tumor mutational burden was confirmed in this study despite common PDL1 expression in FDCS arguing on the efficacy of immune checkpoint inhibitors. CDKN2A deletion, detected by WGS and confirmed by fluorescence in situ hybridization in 41% of cases (9/22) indicates that impairment of cell cycle regulation may sustain oncogenesis in FDCS. Absence of mutations in the RAS/RAF/MAPK pathway and lack of clonal hematopoiesis-related mutations in FDCS sanction its differences from dendritic cell-derived neoplasms of hematopoietic derivation. WGS and WES in FDCS provides additional information on the molecular landscape of this rare tumor, proposing novel candidate genes for innovative therapeutical approaches to improve survival of patients with multifocal disease.

EBV-positive inflammatory follicular dendritic cell sarcoma (EBV+ inflammatory FDCS) is a rare neoplasm almost exclusively located in the spleen or liver. It is characterized by a proliferation of EBV-positive spindle-shaped cells bearing follicular dendritic cell markers, associated with an abundant lymphoplasmacytic infiltrate. EBV+ inflammatory FDCS is often asymptomatic or responsible for mild symptoms. It usually displays an indolent course and its prognosis is excellent after tumor removal, although relapsing and metastatic forms exist. Herein, we describe an aggressive form of splenic EBV+ inflammatory FDCS in a 79-year-old woman presenting with abdominal pain, deterioration of general health status, major inflammatory syndrome, and symptomatic hypercalcemia. A splenectomy was performed leading to a rapid improvement in her clinical condition and normalization of laboratory abnormalities. Unfortunately, her symptoms and laboratory abnormalities reappeared 4 months later. Computed tomography showed a mass in the splenectomy site and multiple liver and peritoneal nodules. Further analyses were performed on tumor tissue and showed positive phospho-ERK staining of tumoral cells indicating activation of MAPK pathway. Inactivating mutations were found on CDKN2A and NF1 genes. Subsequently, the patient's condition deteriorated rapidly. Since interleukin-6 levels were dramatically increased, tocilizumab was used but only had a transient effect on the patient's symptoms and inflammatory syndrome. Antitumor agent gemcitabine was initiated but her clinical condition continued to deteriorate and the patient died 2 weeks later. The management of aggressive forms of EBV+ inflammatory FDCS remains challenging. However, since these tumors seem to display genetic alterations, better characterization could lead to molecular targeted therapies., Competing Interests: Declaration of Conflicting InterestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: Follicular dendritic cell sarcoma (FDCS) is a rare low-grade tumor of the lymph nodes, but roughly one-third of the cases emerge from extranodal sites, posing diagnostic challenges., Case Presentation: In this report, we present the case of a 59-year-old lady who complained of renal colic. During investigation, a kidney tumor was discovered. A radical nephrectomy was performed, and histological examination identified the tumor as a sarcomatoid renal cell carcinoma. The case was then referred to a genitourinary pathologist for further evaluation. The tumor cells exhibited positive staining for CD21, CD23, somatostatin receptor 2 A, and MDM2 expression. Additionally, MDM2 gene amplification was confirmed by the FISH study. Ultimately, the tumor was diagnosed as a primary renal FDCS. The patient was placed under active oncological surveillance and did not receive any further therapy. Remarkably, after 91 months of follow-up, she remains tumor-free., Conclusion: This case represents a well-documented primary renal FDCS. Our aim in presenting this extremely rare tumor is to enhance awareness and highlight the importance of considering FDCS in the differential diagnosis., (© 2024. The Author(s).)

The 5th edition of the World Health Organization classification of hematolymphoid tumors (WHO Blue Book) is soon to be published. Significant revisions have been made in the chapters on histiocytic/dendritic cell neoplasms and stroma-derived neoplasms of lymphoid tissues, leading to the reclassification and renaming of specific diseases. This article provides a concise interpretation and summary of these updates, highlighting the differences from the fourth edition. Pertinent changes from clinical pathological diagnosis to treatment and prognosis are explored, with an emphasis on recent advancements in molecular genetics. Newly introduced disease classifications are discussed, and the section on follicular dendritic cell sarcoma contributed by the author is detailed to assist readers in quickly understanding and assimilating the new classification standards.

Background: Follicular dendritic cell sarcoma (FDCS) is a rare malignancy that arises from follicular dendritic cells and typically presents as a slow-growing painless mass without specific symptoms. Here we report an unusual case of a 55-year-old female with retroperitoneal FDCS who presented with progressive abdominal pain onset and acute exacerbation., Methods: On CTA, a middle-upper abdominal mass (58*40 mm) was shown with multiple enlarged lymph nodes. After en-bloc resection of the tumor, the patient recovered completely from her symptoms and was discharged without complication. One month later, the patient returned for follow-up and the relevant tests were completed., Results: In this case, CA724 elevated significantly and seemed to be associated with tumor progression. The results of positron emission tomography/computed tomography (PET/CT) and radiological examinations, including magnetic resonance imaging (MRI) and computed tomography angiography (CTA), were discussed to improve our understanding of diagnostic tools on FDCS. Targeted genomic sequencing analysis revealed three novel gene mutations, EPHA3 (nonsense mutation), DDR2 (SNV), and BIRC3 (InDel)., Conclusion: We reported an unusual case of retroperitoneal FDCS with acute exacerbated abdominal pain. The interpretations of CA724, PET/CT, as well as imaging results deserve further investigation in FDCS. Genomic sequencing revealed three novel gene mutations in FDCS, including EPHA3 (nonsense mutation), DDR2 (SNV), and BIRC3 (InDel).

Context.—: Despite their stromal origin, follicular dendritic cells (FDCs) share many functions with hematopoietic system cells. FDC neoplasms are currently classified by the World Health Organization along with those of a histiocytic nature. However, the molecular alterations driving oncogenesis in FDC sarcomas (FDCSs) are beginning to be unveiled and do not seem to concur with those described in histiocytic neoplasms, namely MAPK pathway activation., Objective.—: To identify molecular alterations driving tumorigenesis in FDCS., Design.—: We investigated the role of MYC and TP53 in FDC-derived tumor oncogenesis and assessed comprehensively the status of the MAPK pathway in 16 FDCSs, 6 inflammatory pseudotumor (IPT)-like FDCSs, and 8 IPTs., Results.—: MYC structural alterations (both amplifications and rearrangements) were identified in 5 of 14 FDCSs (35.7%), all associated with MYC overexpression. TP53 mutations were identified in 4 of 14 FDCSs (28.6%), all of which displayed intense and diffuse p53 expression. None of these alterations were identified in any IPT-like FDCSs or in IPT cases. No MAPK pathway gene alterations were identified in any of the cases studied., Conclusions.—: The presence of MYC and TP53 alterations and the lack of association with Epstein-Barr virus segregate classical FDCS from IPT-like FDCS, pointing at different oncogenic mechanisms in both entities. Our results suggest a possible oncogenic role of MYC and TP53 alterations in FDCS. The absence of MAPK pathway alterations confirms the lack of a significant role of this pathway in the oncogenesis of FDC-derived neoplasms., Competing Interests: The authors have no relevant financial interest in the products or companies described in this article., (© 2023 College of American Pathologists.)

Background: Histiocytic and dendritic cell neoplasms are a diverse group of tumors arising from monocytic or dendritic cell lineage. Whereas the genomic features for Langerhans cell histiocytosis and Erdheim-Chester disease have been well described, other less common and often aggressive tumors in this broad category remain poorly characterized, and comparison studies across the World Health Organization diagnostic categories are lacking., Methods: Tumor samples from a total of 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs), underwent hybridization capture with analysis of up to 406 cancer-related genes., Results: Among the entire cohort of 102 patients, CDKN2A mutations were most frequent across subtypes and made up 32% of cases, followed by TP53 mutations (22%). Mitogen-activated protein kinase (MAPK) pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCS (72% vs. 0%; p < .0001). In contrast, NF-κB pathway mutations were frequent in FDCSs but rare in M group histiocytoses (61% vs. 12%; p < .0001). Tumor mutational burden was significantly higher in M group histiocytoses as compared with FDCSs (median 4.0/Mb vs. 2.4/Mb; p = .012). We also describe a pediatric patient with recurrent secondary histiocytic sarcoma treated with targeted therapy and interrogated by molecular analysis to identify mechanisms of therapeutic resistance., Conclusion: A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies. Our findings highlight the potential value of molecular testing to enable precise tumor classification, identify candidate oncogenic drivers, and define personalized therapeutic options for patients with these aggressive tumors., Implications for Practice: This study presents comprehensive genomic profiling results on 102 patient cases within four major subtypes of malignant histiocytic and dendritic cell neoplasms, including 44 follicular dendritic cell sarcomas (FDCSs), 41 histiocytic sarcomas (HSs), 7 interdigitating dendritic cell sarcomas (IDCSs), and 10 Langerhans cell sarcomas (LCSs). MAPK pathway mutations were present and enriched among the malignant histiocytosis (M) group (HS, IDCS, and LCS) but absent in FDCSs. In contrast, NF-κB pathway mutations were frequent in FDCSs but rare in M group histiocytosis. A total of 42 patient tumors (41%) harbored pathogenic mutations that were potentially targetable by approved and/or investigative therapies., (© 2021 The Authors. The Oncologist published by Wiley Periodicals LLC on behalf of AlphaMed Press.)

Inflammatory pseudotumor-like follicular/fibroblastic dendritic cell sarcoma (IPT-like FFDCS) is a rare, indolent neoplasm that occurs in the spleen or liver and harbors Epstein-Barr virus (EBV) integrated into the host genome. The molecular genetic characteristics of IPT-like FFDCS have not been well studied and there are no established and actionable molecular features to guide treatment decisions or diagnosis beyond the recognition of viral genome integration. We subjected two cases of IPT-like FFDCS to a comprehensive next-generation sequencing analysis. Several variants of uncertain clinical significance were detected in both tumors. No variants of potential or strong clinical significance were detected within the targeted regions of the evaluated genes. Additionally, no fusion events were detected involving the genes in either tumor. The performed molecular analysis identified no genetic aberrations in IPT-like FFDCS and its genomic landscape remains, with the exception of a monoclonal EBV gene, largely undefined.

Objective: To investigate the clinical pathologic characteristics of extranodal follicular dendritic cell sarcoma (FDCS). Methods: We collected 7 cases of extranodal FDCS, HE staining, immunohistochemical study were performed. The V600E mutation of BRAF in 7 cases were detected by real-time PCR and EBER in situ hybridization was performed on 4 cases. Results: Among the 7 cases of FDCS, 5 cases were male and 2 cases were female, the median age was 55 years old, including 4 cases of low-grade FDCS and 3 cases of high-grade FDCS. The tumor location of 2 cases was in mediastinum, the tumor locations of others were in nasopharynx, kidney, lung, rectum and liver, respectively. The results of immunohistochemistry showed that, the tumor cells were diffusely or focally positive for CD21, CD23, CD35, D2-40, EGFR and CXCL13, but negative for S-100, CD68, HMB45, SMA, Desmin, CD117, Dog-1, CD34, CD30, EMA and CK.Five cases were positive for PD-L1 and the its expression in high-grade FDCS were higher than that in low-grade FDCS.Two cases of low-grade FDCS were positive for BRAF V600E, but the BRAF V600E mutation weren't detected in all of 7 cases. The result of EBER in-situ hybridization showed that only the nasopharynx FDCS was positive.The follow-up information of 5 patients were available (7~43 months), 4 patients died and 1 still alive with rectum metastasis. Conclusions: FDCS is a rare malignant disease with relapse and metastatic tendency. The combined applications of the first-line antibodies including CD21, CD23, CD35 and second-line antibodies including D2-40, CXCL13, EGFR are helpful for its diagnosis and differential diagnosis. The high expression of PD-L1 implicates the potential benefit of FDCS patients acquired from immunotherapy.

Rationale: Follicular dendritic cell (FDC) sarcoma is a rare tumor with FDC differentiation that typically arises within lymph nodes but can also occur extranodally. To date, the primary esophageal FDC sarcoma has not been reported in the English literature., Patient Concerns: We described a 67-year-old female who foremostly presented with dysphagia, and the patient was readmitted due to a dry cough and pain of his right shoulder 2 years after initial treatment., Diagnoses: Primary esophageal FDC sarcoma with the right superior mediastinal lymph node metastasis., Interventions: The esophageal tumor was removed by endoscopic submucosal dissection at the first hospitalization. At the second hospitalization 2 years after the initial visit, the tracheal stent loaded with (125) iodine radioactive seeds was placed. The profiles of genetic variations and immunotherapeutic biomarkers were also explored by next-generation sequencing protocol from the patient's blood, esophageal primary, and mediastinal metastatic tumor samples., Outcomes: The patient's symptom transitorily relieved, but she gave up further treatment and died 2 months after the tracheal stent was placed. As for the genomic alterations, we found 9 gene mutations in all the samples, including checkpoint kinase 2(CHEK2), FAT atypical cadherin 1 (FAT1), tumor protein 53 (TP53), DPYD, ERBB2 interacting protein (ERBB2IP), FBXW7, KMT2D, PPP2R1A, TSC2, whereas amplification of MYC was only in the metastatic example. The analysis of clonal evolution and phylogenetic tree showed the propagation and replay of polyclonal esophageal FDC sarcoma. At the same time, the detection of biomarkers for immunotherapy revealed microsatellite stable and mismatch repair-proficient (pMMR), which predicted a relatively poor anti-programmed death (PD-1)/programmed death ligand (PD-L1) immunotherapy outcome. On the contrary, the tumor mutational burdens were 10 mutations per 1 million bases in both the primary and metastatic tumor sample, which ranked the top 23.3% in solid tumors mutational burdens database of Geneseeq and might be a good predictor of the efficacy of anti-PD-1/PD-L1 immunotherapy., Lessons: To the best of our knowledge, this case report announced the first case of extranodal primary esophageal FDC sarcoma in the world, and firstly revealed its unique genetic alterations profiles, which might contribute to further in-depth study of this rare disease.

Castleman disease (CD) is a rare lymphoproliferative disorder subclassified as unicentric CD (UCD) or multicentric CD (MCD) based on clinical features and the distribution of enlarged lymph nodes with characteristic histopathology. MCD can be further subtyped based on human herpes virus 8 (HHV8) infection into HHV8-associated MCD, HHV8 - /idiopathic MCD (iMCD), and polyneuropathy, organomegaly, endocrinopathy, monoclonal gammopathy, and skin change (POEMS)-associated MCD. In a subset of cases of UCD, an associated follicular dendritic cell sarcoma (FDCS) may be seen. Although numerous reports of the clinical and histologic features of UCD, MCD, and FDCS exist, an understanding of the genetic and epigenetic landscape of these rare diseases is lacking. Given this paucity of knowledge, we analyzed 15 cases of UCD and 3 cases of iMCD by targeted next-generation sequencing (NGS; 405 genes) and 3 cases of FDCS associated with UCD hyaline vascular variant (UCD-HVV) by whole-exome sequencing. Common amplifications of ETS1 , PTPN6 , and TGFBR2 were seen in 1 iMCD and 1 UCD case; the iMCD case also had a somatic DNMT3A L295Q mutation. This iMCD patient also showed clinicopathologic features consistent with a specific subtype known as Castleman-Kojima disease (thrombocytopenia, anasarca, fever, reticulin fibrosis, and organomegaly [TAFRO] clinical subtype). Additionally, 1 case of UCD-HVV showed amplification of the cluster of histone genes on chromosome 6p. FDCS associated with UCD-HVV showed mutations and copy number changes in known oncogenes, tumor suppressors, and chromatin structural-remodeling proteins., (© 2018 by The American Society of Hematology.)

Follicular dendritic cell sarcoma is a rare malignant neoplasm of dendritic cell origin that is currently poorly characterized by genetic studies. To investigate whether recurrent genomic alterations may underlie the biology of follicular dendritic cell sarcoma and to identify potential contributory regions and genes, molecular inversion probe array analysis was performed on 14 independent formalin-fixed, paraffin-embedded samples. Abnormal genomic profiles were observed in 11 out of 14 (79%) cases. The majority showed extensive genomic complexity that was predominantly represented by hemizygous losses affecting multiple chromosomes. Alterations of chromosomal regions 1p (55%), 2p (55%), 3p (82%), 3q (45%), 6q (55%), 7q (73%), 8p (45%), 9p (64%), 11q (64%), 13q (91%), 14q (82%), 15q (64%), 17p (55%), 18q (64%), and 22q (55%) were recurrent across the 11 samples showing abnormal genomic profiles. Many recurrent genomic alterations in follicular dendritic cell sarcoma overlap deletions that are frequently observed across human cancers, suggesting selection, or an active role for these alterations in follicular dendritic cell sarcoma pathogenesis. In support of a tumor suppressor-driven biology, homozygous deletions involving tumor suppressor genes CDKN2A, RB1, BIRC3, and CYLD were also observed. Neither recurrent gains nor amplifications were observed. This genomic characterization provides new information regarding follicular dendritic cell sarcoma biology that may improve understanding about the underlying pathophysiology, provide better prognostication, and identify potential therapeutic markers for this rare disease.

Follicular dendritic cell (FDC) sarcomas are rare mesenchymal tumors with variable clinical, morphologic, and phenotypic characteristics. Transcriptome analysis was performed on multiple FDC sarcomas and compared with other mesenchymal tumors, microdissected Castleman FDCs, and normal fibroblasts. Using unsupervised analysis, FDC sarcomas clustered with microdissected FDCs, distinct from other mesenchymal tumors and fibroblasts. The specific endowment of FDC-related gene expression programs in FDC sarcomas emerged by applying a gene signature of differentially expressed genes ( n = 1,289) between microdissected FDCs and fibroblasts. Supervised analysis comparing FDC sarcomas with microdissected FDCs and other mesenchymal tumors identified 370 and 2,927 differentially expressed transcripts, respectively, and on the basis of pathway enrichment analysis ascribed to signal transduction, chromatin organization, and extracellular matrix organization programs. As the transcriptome of FDC sarcomas retained similarity with FDCs, the immune landscape of FDC sarcoma was investigated by applying the CIBERSORT algorithm to FDC sarcomas and non-FDC mesenchymal tumors and demonstrated that FDC sarcomas were enriched in T follicular helper (T FH ) and T regulatory (T REG ) cell populations, as confirmed in situ by immunohistochemistry. The enrichment in specific T-cell subsets prompted investigating the mRNA expression of the inhibitory immune receptor PD-1 and its ligands PD-L1 and PD-L2, which were found to be significantly upregulated in FDC sarcomas as compared with other mesenchymal tumors, a finding also confirmed in situ Here, it is demonstrated for the first time the transcriptional relationship of FDC sarcomas with nonmalignant FDCs and their distinction from other mesenchymal tumors. Implications: The current study provides evidence of a peculiar immune microenvironment associated with FDC sarcomas that may have clinical utility. Mol Cancer Res; 15(5); 541-52. ©2017 AACR ., (©2017 American Association for Cancer Research.)

Follicular dendritic cell sarcoma is a rare tumor that typically arises within lymph nodes but can also occur extranodally. It is important to have a high index of suspicion, so follicular dendritic cell sarcoma is included in the differential diagnosis of a spindle cell neoplasm in the appropriate clinical and morphologic settings. When included in the differential diagnosis, immunohistochemistry is generally sufficient to substantiate the diagnosis of follicular dendritic cell sarcoma. In this review, we discuss the clinicopathologic features of follicular dendritic cell sarcoma, recent molecular and cytogenetic findings, prognosis, and current approaches to treatment.

Follicular dendritic cell (FDC)-sarcoma is a rare neoplasm with morphologic and phenotypic features of FDCs. It shows an extremely heterogeneous morphology, therefore, its diagnosis relys on the phenotype of tumor cells. Aim of the present study was the identification of new specific markers for FDC-sarcoma by whole transcriptome sequencing (WTS). Candidate markers were selected based on gene expression level and biological function. Immunohistochemistry was performed on reactive tonsils, on 22 cases of FDC-sarcomas and 214 control cases including 114 carcinomas, 87 soft tissue tumors, 5 melanomas, 5 thymomas and 3 interdigitating dendritic cell sarcomas. FDC secreted protein (FDCSP) and Serglycin (SRGN) proved to be specific markers of FDC and related tumor. They showed better specificity and sensitivity values than some well known markers used in FDC sarcoma diagnosis (specificity: 98.6%, and 100%, respectively; sensitivity: 72.73% and 68.18%, respectively). In our cohorts CXCL13, CD21, CD35, FDCSP and SRGN were the best markers for FDC-sarcoma diagnosis and could discriminate 21/22 FDC sarcomas from other mesenchymal tumors by linear discriminant analysis. In summary, by WTS we identified two novel FDC markers and by the analysis of a wide cohort of cases and controls we propose an efficient marker panel for the diagnosis of this rare and enigmatic tumor.

The 2008 World Health Organization (WHO) diagnostic criteria of histiocytic and dendritic cell neoplasms from hematopoietic and lymphoid tissues no longer required the absence of clonal B-cell/T-cell receptor gene rearrangements. It is true that the clonal B-cell/T-cell receptor gene rearrangements have been identified in rare cases of histiocytic and dendritic cell neoplasms, such as those with or following lymphoma/leukemia or in some sporadic histiocytic/dendritic cell sarcomas, but the clonal features of such group of tumor are still not clear. Here we investigated the clonal status of 33 samples including Langerhans cell histiocytosis (LCH), Langerhans cell sarcoma (LCS), follicular dendritic cell sarcoma (FDCS), interdigitating dendritic cell sarcoma (IDCS) and histiocytic sarcoma (HS). Among them, twenty-eight cases were sporadic without current or past lymphoma/leukemia. Three cases were found with a past history of T-cell lymphoma, one case was followed by extraosseous plasmacytoma, and one case was found with diffuse large B-cell lymphoma (DLBCL). Our results showed that there was a high frequency of clonal IG and T-cell receptor gene rearrangements in these cases. Notably, 4 cases of LCH and 2 cases of FDCS showed both B and T cell receptor gene rearrangements concurrently. One case of FDCS synchronous with DLBCL showed identical clonal IGH in both tumor populations and clonal TCRβ in FDCS alone. No matter if the presence of clonal receptor gene rearrangements was associated with the tumor origin or tumorigenesis, it might serve as a novel tumor marker for developing target therapy.

Follicular dendritic cell (FDC) sarcomas are rare mesenchymal tumours, which are fatal in 20% of the patients and usually occur in secondary lymphoid organs or extranodal localizations. Due to the rareness of these tumours, only few studies have been conducted on molecular level. In the present study, we performed microRNA (miRNA) profiling of 31 FDC sarcomas and identified two subgroups, one with high miRNA expression and the other group with low miRNA expression levels. The first group showed a strong similarity to fibroblasts and myopericytomas, whereas the second group was more closely related to FDCs from Castleman's disease. Both groups showed important differences compared with myeloid-derived dendritic cells, confirming mesenchymal origin of FDCs and their derived sarcomas. The two FDC sarcoma groups did not differ on morphological grounds, mitotic activity or BRAF mutation status. However, patients of group I presented a tendency to a shorter overall survival and more frequent podoplanin expression by immunohistochemistry. The importance of these newly recognized FDC sarcoma subgroups in terms of clinical behaviour and therapeutic implications should be assessed in a larger cohort in future studies., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Background: Follicular dendritic cell sarcoma is a rare tumour with clinical behaviour covering a spectrum from indolent to aggressive disease. Treatment recommendations are currently based on case reports and small series describing combinations of surgery, chemotherapy and radiotherapy providing the best patient outcomes. Recent knowledge on molecular aberrations in this disease have not yet impacted on therapeutic decisions., Case Presentation: We describe a case of progressive follicular dendritic cell sarcoma of the lung and pleura, treated based on knowledge of the tumour's molecular aberrations. The patient was initially treated with surgery, chemotherapy and radiotherapy and developed disease progression. Mutation testing by Caris molecular intelligence demonstrated a breast cancer 2 gene mutation and further treatment with carboplatin and veliparib achieved disease stabilisation., Conclusion: Understanding of the molecular profile of rare tumours is key to improve therapeutic decision making and patient outcomes.

Follicular dendritic cell sarcoma is an uncommon neoplastic proliferation of spindled to ovoid cells with morphologic and immunophenotypic features similar to normal follicular dendritic cells. While most follicular dendritic cell sarcomas arise from lymph nodes, at least one-third occur in extranodal sites. A broad differential diagnosis can be developed--as this tumor has morphologic features similar to other tumors, hence creating a diagnostic pitfall--but its immunophenotypic profile is quite specific and is diagnostically crucial. Herein, we review the pathogenesis; histologic morphology; and immunohistochemical, electron microscopy, and clinical features, including treatment and prognosis, of follicular dendritic cell sarcomas. We will briefly describe the role of molecular studies including utility of BRAF mutations in diagnosing this tumor.

Follicular dendritic cell sarcoma is a rare mesenchymal neoplasm with a variable and unpredictable clinical course. The genetic alterations that drive tumorigenesis in follicular dendritic cell sarcoma are largely unknown. One recent study performed BRAF sequencing and found V600E mutations in 5 of 27 (19%) cases. No other recurrent genetic alterations have been reported. The aim of the present study was to identify somatic alterations in follicular dendritic cell sarcoma by targeted sequencing of a panel of 309 known cancer-associated genes. DNA was isolated from formalin-fixed paraffin-embedded tissue from 13 cases of follicular dendritic cell sarcoma and submitted for hybrid capture-based enrichment and massively parallel sequencing with the Illumina HiSeq 2500 platform. Recurrent loss-of-function alterations were observed in tumor suppressor genes involved in the negative regulation of NF-κB activation (5 of 13 cases, 38%) and cell cycle progression (4 of 13 cases, 31%). Loss-of-function alterations in the NF-κB regulatory pathway included three cases with frameshift mutations in NFKBIA and two cases with bi-allelic loss of CYLD. Both cases with CYLD loss were metastases and carried concurrent alterations in at least one cell cycle regulatory gene. Alterations in cell cycle regulatory genes included two cases with bi-allelic loss of CDKN2A, one case with bi-allelic loss of RB1, and one case with a nonsense mutation in RB1. Last, focal copy-number gain of chromosome 9p24 including the genes CD274 (PD-L1) and PDCD1LG2 (PD-L2) was noted in three cases, which represents a well-described mechanism of immune evasion in cancer. These findings provide the first insight into the unique genomic landscape of follicular dendritic cell sarcoma and suggest shared mechanisms of tumorigenesis with a subset of other tumor types, notably B-cell lymphomas.

The histiocytoses are rare tumors characterized by the primary accumulation and tissue infiltration of histiocytes and dendritic cells. Identification of the activating BRAFV600E mutation in Erdheim-Chester disease (ECD) and Langerhans cell histiocytosis (LCH) cases provided the basis for the treatment with BRAF and/or MEK inhibitors, but additional treatment options are needed. Twenty-four cases of neoplastic histiocytic diseases [11 extrapulmonary LCH, 4 ECD, 4 extranodal Rosai-Dorfman disease (RDD), 3 follicular dendritic cell sarcoma (FDCS), 1 histiocytic sarcoma (HS) and 1 blastic plasmacytoid dendritic cell neoplasm (BPDCN)] were analyzed using immunohistochemical and mutational analysis in search of biomarkers for targeted therapy. BRAF V600E mutations were detected in 4/11 LCH and 4/4 ECD cases. A pathogenic PTEN gene mutation and loss of PTEN protein expression were identified in the case of HS. Increased expression of PD-L1 (≥2+/≥5%) was seen in 3/4 ECD, 7/8 LCH, 3/3 FDCS and 1/1 HS, with overall 81% concordance between 2 antibodies used in the study (SP142 vs. MAB1561 clone). These results show for the first time significant expression of the PD-L1 immune checkpoint protein in these disorders, which may provide rationale for addition of immune check-point inhibitors in treatment of disseminated and/or refractory histiocytoses.

Background: The identification of chromosomal abnormalities in many hematopoietic and mesenchymal neoplasms has contributed significantly to classification systems. Follicular dendritic cell (FDC) sarcoma is an intermediate-grade malignancy with morphological and immunophenotypic features of follicular dendritic cells. Available data on genetic changes in this neoplasm are limited, with only isolated case reports of cytogenetic abnormalities., Case Report: We reviewed histological, immunophenotypic and cytogenetic findings in two cases of FDC sarcoma. The two cases of FDC sarcoma, were observed in female patients, one was nodal and one extranodal and they exhibited relatively complex karyotypes, characterized by structural abnormalities and loss of multiple chromosomes. One patient had several disease recurrences. At the last follow-up both patients were alive with no residual disease., Conclusion: The cytogenetic findings in these two cases, coupled with the few previously described abnormal karyotypes, suggest that FDC sarcoma is cytogenetically diverse.

Both interdigitating cell sarcoma (IDCS) and follicular dendritic cell sarcoma (FDCS) are rare neoplasms derived from dendritic cells in lymphoid organs. IDCS is defined as a neoplastic proliferation of spindle-shaped to ovoid cells with phenotypic features similar to those of IDCs. FDCS is a malignant neoplasm derived from FDCs that possess and present antigens to B cells in the follicular (germinal) centers of lymphoid organs. They often occur in lymph nodes, although they can also arise at extranodal sites. In this review, we have highlighted the morphological and immunohistochemical properties of these neoplasms, which could help in unequivocal and accurate diagnosis.

Follicular dendritic cell (FDC) sarcoma, especially of extranodal origin, is an extremely rare malignancy of FDC origin, with only 1 case previously documented in the thyroid. The authors report the case of a 58-year-old female who presented with a painless mass in her neck. The neoplastic cells expressed monocyte/macrophage-specific marker CD68 (KP-1) and lysozymes and the dendritic cell-associated antigens CD35 and Fascin but was negative for CD1a, CD21, and CD23, most consistent with a diagnosis of FDC sarcoma. BIOMED-2 multiplex polymerase chain reaction analysis showed B-cell clonality in both tumor and its adjacent coexisting Hashimoto's thyroiditis. To the authors' knowledge, this is the first report of a rare entity of FDC sarcoma primarily involving the thyroid gland coexisting with Hashimoto's thyroiditis.

Background: Follicular dendritic cell (FDC) sarcoma is a rare low-to-intermediate grade malignant dendritic cell neoplasm that often has an indolent clinical course. FDC sarcomas are often misdiagnosed on aspiration cytology., Case: A 26-year-old woman presented with a solid, slowly growing, painless mass in her right neck for 3 months. Computed tomography revealed a 3.6-cm, well-defined homogenous solid mass located posterior to the mandible and submandibular glands. Fine needle aspiration cytology revealed many large, spindle to ovoid epithelioid cells in singles, small clusters, and syncytial sheets with moderate to abundant cytoplasm, indistinct cell borders, irregular nuclear membrane, fine to vesicular chromatin, and conspicuous nucleoli. The background contained many small mature lymphocytes intimately mixed with large epithelioid tumor cells. Tumor cells were strongly positive for CD21, CD35, CD23, and fascin. Diagnosis of FDC sarcoma was rendered; follow-up surgical resection and ultrastructural study confirmed the diagnosis. The cytogenetic study showed a normal female karyotype 46,XX., Conclusion: Although the cytomorphology of FDC sarcoma is characteristic, a preoperative diagnosis of FDC sarcoma based on fine needle aspiration cytology is very challenging, if not impossible. Immunohistochemistry is always necessary for rendering and/or confirming the diagnosis, and ultrastructural studies are helpful.

The diagnosis of histiocytic/dendritic cell (H/DC) sarcomas is currently based on morphology and the presence of immunophenotypic features of H/DC differentiation. The issue whether clonal immunoglobulin receptor gene rearrangements are present in H/DC sarcomas has been debated over decades until the recent data by Feldman et al, which provided compelling evidence that patients with follicular lymphoma and concurrent/synchronous H/DC sarcoma share identical genotypic features, suggested the possibility of transdifferentiation or dedifferentiation of 2 otherwise morphologically and immunophenotypically distinctive neoplasms. Here we investigated the molecular characteristics of 23 patients with sporadic H/DC sarcoma. Nine of the 23 cases (39%) showed clonal IGH (+/-IGK) gene rearrangements, whereas 2 (9%) cases showed only clonal IGK gene rearrangements, which were further validated and confirmed by direct DNA sequencing. One histiocytic sarcoma showed t(14;18) by quantitative-polymerase chain reaction, which was confirmed by fluorescence in situ hybridization analysis showing IGH/BCL2 fusions in neoplastic histiocytes. Notably, all IGH/IGK-positive H/DC sarcomas were negative for B-cell-associated transcription factors PAX5 and BOB.1, whereas 4 of 7 IGH/IGK-positive histiocytic sarcoma cases were positive for Oct2. In addition, no evidence of Epstein-Barr virus infection was detected in 8 of 11 IGH/IGK-positive H/DC sarcoma cases by in situ hybridization, suggesting that Epstein-Barr virus infection may not play an important role in the pathogenesis of these tumors. This study provides evidence that clonal immunoglobulin receptor gene rearrangements may be detected at a high frequency in sporadic H/DC sarcomas. The findings suggest that a large subset of H/DC sarcomas have inherited B-cell genotypes, thus providing new insights for the pathogenesis of these rare but aggressive neoplasms.

The case of a patient with follicular dendritic cell (FDC) sarcoma with chromosomal aberration add(21)(q11.2) is described. Cytogenetic studies showed the karyotype 46,XX,add(21)(q11.2)[3]/46,XX[17], although the encoded protein involved was not clarified. The abnormal pattern was quite simple, and different from a previous report. The clinical course of the FDC sarcoma in this case has been indolent, as for most FDC sarcoma patients. Although this patient suffered from breast carcinoma 6 years after the onset of FDC sarcoma, the carcinoma showed different histological and phenotypic profiles.

Rare cases of histiocytic and dendritic cell (H/DC) neoplasms have been reported in patients with follicular lymphoma (FL), but the biologic relationship between the 2 neoplasms is unknown. We studied 8 patients with both FL and H/DC neoplasms using immunohistochemistry, fluorescence in situ hybridization (FISH) for t(14;18), and polymerase chain reaction (PCR)/sequencing of BCL2 and IGH rearrangements. There were 5 men and 3 women (median age, 59 years). All cases of FL were positive for t(14;18). The H/DC tumors included 7 histiocytic sarcomas, 5 of which showed evidence of dendritic differentiation, and 1 interdigitating cell sarcoma. Five H/DC tumors were metachronous, following FL by 2 months to 12 years; tumors were synchronous in 3. All 8 H/DC tumors showed presence of the t(14;18) either by FISH, or in 2 cases by PCR with the major breakpoint region (MBR) probe. PCR and sequencing identified identical IGH gene rearrangements or BCL2 gene breakpoints in all patients tested. All H/DC tumors lacked PAX5, and up-regulation of CEBPbeta and PU.1 was seen in all cases tested. These results provide evidence for a common clonal origin of FL and H/DC neoplasms when occurring in the same patient, and suggest that lineage plasticity may occur in mature lymphoid neoplasms.