CDKs in Sarcoma: Mediators of Disease and Emerging Therapeutic Targets.

Sarcomas represent one of the most challenging tumor types to treat due to their diverse nature and our incomplete understanding of their underlying biology. Recent work suggests cyclin-dependent kinase (CDK) pathway activation is a powerful driver of sarcomagenesis. CDK proteins participate in numerous cellular processes required for normal cell function, but their dysregulation is a hallmark of many pathologies including cancer. The contributions and significance of aberrant CDK activity to sarcoma development, however, is only partly understood. Here, we describe what is known about CDK-related alterations in the most common subtypes of sarcoma and highlight areas that warrant further investigation. As disruptions in CDK pathways appear in most, if not all, subtypes of sarcoma, we discuss the history and value of pharmacologically targeting CDKs to combat these tumors. The goals of this review are to (1) assess the prevalence and importance of CDK pathway alterations in sarcomas, (2) highlight the gap in knowledge for certain CDKs in these tumors, and (3) provide insight into studies focused on CDK inhibition for sarcoma treatment. Overall, growing evidence demonstrates a crucial role for activated CDKs in sarcoma development and as important targets for sarcoma therapy.

Atypical lipomatous tumour/well-differentiated liposarcoma and de-differentiated liposarcoma in patients aged ≤ 40 years: a study of 116 patients.

AIMS: Limited data exist on atypical lipomatous tumour (ALT)/well-differentiated liposarcoma (WDL) and de-differentiated liposarcoma (DDLPS) in children and young adults. METHODS AND RESULTS: Cases of ALT/WDL/DDLPS arising in patients aged ≤ 40 years were collected from multiple institutional and consultation archives. A total of 116 cases of ALT/WDL (75) and DDLPS (41) were identified, representing fewer than 5% of these tumours seen at our institutions during this time-period. The patients (59 male/57 female) ranged in age from 8 to 40 years. Sites included deep central (abdomen/retroperitoneum/pelvis/groin) (n = 60), extremity (n = 42), trunk (n = 5), head/neck (n = 8) and mediastinum (n = 1). De-differentiated patterns included: high-grade pleomorphic sarcoma, myxofibrosarcoma-like, heterologous rhabdomyoblastic differentiation, low-grade spindle cell sarcoma and homologous lipoblastic differentiation. Forty-one patients experienced a local recurrence and 11 patients with DDLPS developed metastasis. ALT arising in the extremities had lower recurrence rates than deep central WDL (5-year recurrence-free survival 88.9% versus 59.0%; P = 0.002), while patients with deep central DDLPS experienced significantly more adverse events compared to WDL at this site (5-year event-free survival 11.9% versus 59.0%) (P < 0.0001). Seven (of eight) head/neck tumours had follow-up available; five recurred, and one patient (DDLPS) with recurrence also experienced a metastasis. The single mediastinal tumour (DDLPS) recurred and metastasised. CONCLUSION: ALT/WDL and DDLPS occurring in patients aged ≤ 40 years is rare, but exhibits similar morphological features to its counterparts in older adults, including potential for heterologous and homologous de-differentiation in the latter. Although case numbers are limited, tumours arising in the head and neck exhibit high rates of adverse events, suggesting that classification as WDL rather than ALT is more appropriate.

A case of primary cutaneous Ewing sarcoma in a neutropenic patient.

Primary cutaneous Ewing sarcoma is a rare clinical presentation of Ewing sarcoma, usually occurring as a small, localized tumor on the extremities of young adults and associated with favorable prognosis. We report a case of primary cutaneous Ewing sarcoma, which presented on the sole of the foot of a 27-year-old patient with relapsed acute myeloid leukemia and neutropenia. Diagnosis was determined through histological features and staining, as well as fluorescence in situ hybridization and molecular testing. The patient underwent wide-local excision with plan to begin targeted chemotherapy, but unfortunately died from adenovirus pneumonia while neutropenic before targeted chemotherapy was initiated.

Improved survival for extremity soft tissue sarcoma treated in high-volume facilities.

BACKGROUND AND OBJECTIVES: The purpose of this investigation was to determine the effect of hospital volume on treatment decisions, treatment results, and overall patient survival in extremity soft tissue sarcoma. METHODS: The National Cancer Database was used to identify patients ≥18 years of age with non-metastatic soft tissue sarcoma of the extremity treated with surgery. Patients in high- and low-volume centers were matched by propensity score and placed into two equal comparative groups of 2437 patients each. RESULTS: Chemotherapy was used at a higher rate in high-volume centers (22% vs 17%, P < 0.001) and external beam radiation usage was similar (55% vs 52%, P = 0.108). There was a lower incidence of positive margins in high-volume centers (12% vs 17%, P < 0.001). There was no significant difference in the rates of limb salvage surgery or readmissions at high-volume hospitals compared to low-volume. In a multivariate Cox proportional hazards model, low-volume facilities demonstrated diminished overall survival at all time points (hazard ratio at 5 years = 1.24, 95%CI 1.10-1.39). CONCLUSIONS: Treatment at high-volume hospitals was associated with fewer positive margins and increased overall survival at 2, 5, and 10 years. Continued efforts should focus on optimizing the balance between patient access to specialty care and experience of the treating center.

Anchored multiplex PCR for targeted next-generation sequencing reveals recurrent and novel USP6 fusions and upregulation of USP6 expression in aneurysmal bone cyst.

Primary aneurysmal bone cyst (ABC) is a neoplastic process due to recurrent translocations involving the USP6 gene. By fluorescence in situ hybridization, up to 69% of primary ABCs harbored USP6 translocations; no USP6 translocation was found in secondary ABC or giant cell tumor of bone (GCT). GCT can recur locally, metastasize to the lungs in some cases, and rarely undergo malignant transformation. Differentiating primary ABC from its mimics is important for treatment and prognosis. We evaluated USP6 fusion and expression in 13 cases of primary and 1 case of secondary ABC, and 9 cases of GCT using nucleic acid extracted from formalin-fixed, paraffin-embedded tissue and a next generation sequencing (NGS)-based assay. USP6 fusions including 7 novel fusions and USP6 transcripts were identified in all 13 primary ABCs. Nine cases with strong evidence of fusions showed high levels of USP6 transcripts by reverse transcription-PCR (RT-PCR). The remaining four had no detectable USP6 expression by a first-round of RT-PCR but the presence of USP6 transcripts was identified by a second-round, nested PCR. The major fusions were confirmed by RT-PCR followed by Sanger sequencing. No USP6 fusion or transcript was detected in any of the GCTs or the case of secondary ABC by NGS or by two rounds of PCR. All USP6 translocations resulted in fusion of the entire USP6 coding sequence with promoters of the fusion gene leading to upregulation of USP6 transcription, which is likely the underlying mechanism for ABC oncogenesis. © 2016 Wiley Periodicals, Inc.

Superoxide Dismutase Mimetic Avasopasem Manganese Enhances Radiation Therapy Effectiveness in Soft Tissue Sarcomas and Accelerates Wound Healing.

Soft tissue sarcomas (STSs) are mesenchymal malignant lesions that develop in soft tissues. Despite current treatments, including radiation therapy (RT) and surgery, STSs can be associated with poor patient outcomes and metastatic recurrences. Neoadjuvant radiation therapy (nRT), while effective, is often accompanied by severe postoperative wound healing complications due to damage to the surrounding normal tissues. Thus, there is a need to develop therapeutic approaches to reduce nRT toxicities. Avasopasem manganese (AVA) is a selective superoxide dismutase mimetic that protects against IR-induced oral mucositis and lung fibrosis. We tested the efficacy of AVA in enhancing RT in STSs and in promoting wound healing. Using colony formation assays and alkaline comet assays, we report that AVA selectively enhanced the STS (liposarcoma, fibrosarcoma, leiomyosarcoma, and MPNST) cellular response to radiation compared to normal dermal fibroblasts (NDFs). AVA is believed to selectively enhance radiation therapy by targeting differential hydrogen peroxide clearance in tumor cells compared to non-malignant cells. STS cells demonstrated increased catalase protein levels and activity compared to normal fibroblasts. Additionally, NDFs showed significantly higher levels of GPx1 activity compared to STSs. The depletion of glutathione using buthionine sulfoximine (BSO) sensitized the NDF cells to AVA, suggesting that GPx1 may, in part, facilitate the selective toxicity of AVA. Finally, AVA significantly accelerated wound closure in a murine model of wound healing post RT. Our data suggest that AVA may be a promising combination strategy for nRT therapy in STSs.

Abl kinases can function as suppressors of tumor progression and metastasis.

Introduction: Abl family kinases function as proto-oncogenes in various leukemias, and pro-tumor functions have been discovered for Abl kinases in many solid tumors as well. However, a growing body of evidence indicates that Abl kinases can function to suppress tumor cell proliferation and motility and tumor growth in vivo in some settings. Methods: To investigate the role of Abl kinases in tumor progression, we used RNAi to generate Abl-deficient cells in a model of androgen receptor-indifferent, metastatic prostate cancer. The effect of Abl kinase depletion on tumor progression and metastasis was studied in an in vivo orthotopic model, and tumor cell motility, 3D growth, and signaling was studied in vitro. Results: Reduced Abl family kinase expression resulted in a highly aggressive, metastatic phenotype in vivo that was associated with AKT pathway activation, increased growth on 3D collagen matrix, and enhanced cell motility in vitro. Inhibiting AKT pathway signaling abolished the increased 3D growth of Abl-deficient cells, while treatment with the Abl kinase inhibitor, imatinib, promoted 3D growth of multiple additional tumor cell types. Moreover, Abl kinase inhibition also promoted soft-agar colony formation by pre-malignant fibroblasts. Conclusions: Collectively, our data reveal that Abl family kinases can function to suppress malignant cell phenotypes in vitro, and tumor progression and metastasis in vivo.

CDK4/6-MEK Inhibition in MPNSTs Causes Plasma Cell Infiltration, Sensitization to PD-L1 Blockade, and Tumor Regression.

PURPOSE: Malignant peripheral nerve sheath tumors (MPNST) are lethal, Ras-driven sarcomas that lack effective therapies. We investigated effects of targeting cyclin-dependent kinases 4 and 6 (CDK4/6), MEK, and/or programmed death-ligand 1 (PD-L1) in preclinical MPNST models. EXPERIMENTAL DESIGN: Patient-matched MPNSTs and precursor lesions were examined by FISH, RNA sequencing, IHC, and Connectivity-Map analyses. Antitumor activity of CDK4/6 and MEK inhibitors was measured in MPNST cell lines, patient-derived xenografts (PDX), and de novo mouse MPNSTs, with the latter used to determine anti-PD-L1 response. RESULTS: Patient tumor analyses identified CDK4/6 and MEK as actionable targets for MPNST therapy. Low-dose combinations of CDK4/6 and MEK inhibitors synergistically reactivated the retinoblastoma (RB1) tumor suppressor, induced cell death, and decreased clonogenic survival of MPNST cells. In immune-deficient mice, dual CDK4/6-MEK inhibition slowed tumor growth in 4 of 5 MPNST PDXs. In immunocompetent mice, combination therapy of de novo MPNSTs caused tumor regression, delayed resistant tumor outgrowth, and improved survival relative to monotherapies. Drug-sensitive tumors that regressed contained plasma cells and increased cytotoxic T cells, whereas drug-resistant tumors adopted an immunosuppressive microenvironment with elevated MHC II-low macrophages and increased tumor cell PD-L1 expression. Excitingly, CDK4/6-MEK inhibition sensitized MPNSTs to anti-PD-L1 immune checkpoint blockade (ICB) with some mice showing complete tumor regression. CONCLUSIONS: CDK4/6-MEK inhibition induces a novel plasma cell-associated immune response and extended antitumor activity in MPNSTs, which dramatically enhances anti-PD-L1 therapy. These preclinical findings provide strong rationale for clinical translation of CDK4/6-MEK-ICB targeted therapies in MPNST as they may yield sustained antitumor responses and improved patient outcomes.

TAZ/YAP fusion proteins: mechanistic insights and therapeutic opportunities.

The Hippo pathway is dysregulated in many different cancers, but point mutations in the pathway are rare. Transcriptional co-activator with PDZ-binding motif (TAZ) and Yes-associated protein (YAP) fusion proteins have emerged in almost all major cancer types and represent the most common genetic mechanism by which the two transcriptional co-activators are activated. Given that the N termini of TAZ or YAP are fused to the C terminus of another transcriptional regulator, the resultant fusion proteins hyperactivate a TEAD transcription factor-based transcriptome. Recent advances show that the C-terminal fusion partners confer oncogenic properties to TAZ/YAP fusion proteins by recruiting epigenetic modifiers that promote a hybrid TEAD-based transcriptome. Elucidating these cooperating epigenetic complexes represents a strategy to identify new therapeutic approaches for a pathway that has been recalcitrant to medical therapy.

PRC2 loss drives MPNST metastasis and matrix remodeling.

The histone methyltransferase PRC2 plays a complex role in cancer. Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas with frequent loss-of-function mutations in PRC2 that are associated with poor outcome. Here, we identify a critical role for PRC2 loss in driving MPNST metastasis. PRC2-dependent metastatic phenotypes included increased collagen-dependent invasion, upregulation of matrix-remodeling enzymes, and elevated lung metastasis in orthotopic mouse models. Furthermore, clinical sample analysis determined that PRC2 loss correlated with metastatic disease, increased fibrosis, and decreased survival in patients with MPNSTs. These results may have broad implications for PRC2 function across multiple cancers and provide a strong rationale for investigating potential therapies targeting ECM-remodeling enzymes and tumor fibrosis to improve outcomes in patients with MPNSTs.

Oncogenic RABL6A promotes NF1-associated MPNST progression in vivo.

Background: Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas with complex molecular and genetic alterations. Powerful tumor suppressors CDKN2A and TP53 are commonly disrupted along with NF1, a gene that encodes a negative regulator of Ras. Many additional factors have been implicated in MPNST pathogenesis. A greater understanding of critical drivers of MPNSTs is needed to guide more informed targeted therapies for patients. RABL6A is a newly identified driver of MPNST cell survival and proliferation whose in vivo role in the disease is unknown. Methods: Using CRISPR-Cas9 targeting of Nf1 + Cdkn2a or Nf1 + Tp53 in the mouse sciatic nerve to form de novo MPNSTs, we investigated the biological significance of RABL6A in MPNST development. Terminal tumors were evaluated by western blot, qRT-PCR, and immunohistochemistry. Results: Mice lacking Rabl6 displayed slower tumor progression and extended survival relative to wildtype animals in both genetic contexts. YAP oncogenic activity was selectively downregulated in Rabl6-null, Nf1 + Cdkn2a lesions whereas loss of RABL6A caused upregulation of the CDK inhibitor, p27, in all tumors. Paradoxically, both models displayed elevated Myc protein and Ki67 staining in terminal tumors lacking RABL6A. In Nf1 + p53 tumors, cellular atypia and polyploidy were evident and increased by RABL6A loss. Conclusions: These findings demonstrate that RABL6A is required for optimal progression of NF1 mutant MPNSTs in vivo in both Cdkn2a and p53 inactivated settings. However, sustained RABL6A loss may provide selective pressure for unwanted alterations, including increased Myc, cellular atypia, and polyploidy, that ultimately promote a hyper-proliferative tumor phenotype akin to drug-resistant lesions.

Combination therapies for MPNSTs targeting RABL6A-RB1 signaling.

Precision medicine relies on a detailed molecular understanding of disease pathogenesis. Here, we consider urgently needed therapeutic options for malignant peripheral nerve sheath tumors (MPNSTs) based on emerging insights into druggable pathway alterations found to drive this deadly cancer. Recent observations demonstrate an essential role for an oncogenic GTPase, RABL6A, in promoting MPNST progression through hyperactivation of cyclin-dependent kinases (CDKs) and inactivation of the retinoblastoma (RB1) tumor suppressor. Monotherapies with CDK4/6 inhibitors have shown limited efficacy and durability in pre-clinical studies of MPNSTs and in clinical studies of other tumors. Therefore, we discuss the rationale and clinical benefits of inhibiting multiple RABL6A effectors, particularly CDK4/6 and MEK kinases, in targeted combination therapies suitable for MPNSTs and other Ras-driven malignancies.

Prognostic and therapeutic value of the Hippo pathway, RABL6A, and p53-MDM2 axes in sarcomas.

Additional prognostic and therapeutic biomarkers effective across different histological types of sarcoma are needed. Herein we evaluate expression of TAZ and YAP, the p53-MDM2 axis, and RABL6A, a novel oncoprotein with potential ties to both pathways, in sarcomas of different histological types. Immunohistochemical staining of a tissue microarray including 163 sarcomas and correlation with clinical data showed that elevated YAP and TAZ independently predict worse overall and progression-free survival, respectively. In the absence of p53 expression, combined TAZ and YAP expression adversely affect overall, progression free, and metastasis free survival more than TAZ or YAP activation alone. RABL6A independently predicted shorter time to metastasis and was positively correlated with p53, MDM2 and YAP expression, supporting a possible functional relationship between the biomarkers. Network analysis further showed that TAZ is positively correlated with MDM2 expression. The data implicate all five proteins as clinically relevant downstream players in the Hippo pathway. Finally, a novel inhibitor of MDM2 (MA242), effectively suppressed the survival of sarcoma cell lines from different histological types regardless of p53 status. These findings suggest both independent and cooperative roles for all five biomarkers across different histological types of sarcoma in predicting patient outcomes and potentially guiding future therapeutic approaches.

TAZ-CAMTA1 and YAP-TFE3 alter the TAZ/YAP transcriptome by recruiting the ATAC histone acetyltransferase complex.

Epithelioid hemangioendothelioma (EHE) is a vascular sarcoma that metastasizes early in its clinical course and lacks an effective medical therapy. The TAZ-CAMTA1 and YAP-TFE3 fusion proteins are chimeric transcription factors and initiating oncogenic drivers of EHE. A combined proteomic/genetic screen in human cell lines identified YEATS2 and ZZZ3, components of the Ada2a-containing histone acetyltransferase (ATAC) complex, as key interactors of both fusion proteins despite the dissimilarity of the C terminal fusion partners CAMTA1 and TFE3. Integrative next-generation sequencing approaches in human and murine cell lines showed that the fusion proteins drive a unique transcriptome by simultaneously hyperactivating a TEAD-based transcriptional program and modulating the chromatin environment via interaction with the ATAC complex. Interaction of the ATAC complex with both fusion proteins indicates that it is a key oncogenic driver and unifying enzymatic therapeutic target for this sarcoma. This study presents an approach to mechanistically dissect how chimeric transcription factors drive the formation of human cancers.

The proliferation of human cells is tightly regulated to ensure that enough cells are made to build and repair organs and tissues, while at the same time stopping cells from dividing uncontrollably and damaging the body. To get the right balance, cells rely on physical and chemical cues from their environment that trigger the biochemical signals that regulate two proteins called TAZ and YAP. These proteins control gene activity by regulating the rate at which genes are copied to produce proteins. If this process becomes dysregulated, cells can grow uncontrollably, causing cancer. In cancer cells, it is common to find TAZ and YAP fused to other proteins. In epithelioid hemangioendothelioma, a rare cancer that grows in the blood vessels, cancerous growth can be driven by a version of TAZ fused to the protein CAMTA1, or a version of YAP fused to the protein TFE3. While the role of TAZ and YAP in promoting gene activity is known, it is unclear how CAMTA1 and TFE3 contribute to cell growth becoming dysregulated. Merritt, Garcia et al. studied sarcoma cell lines to show that these two fusion proteins, TAZ-CAMTA1 and YAP-TFE3, change the pattern of gene activity seen in the cells compared to TAZ or YAP alone. An analysis of molecules that interact with the two fusion proteins identified a complex called ATAC as the cause of these changes. This complex adds chemical markers to DNA-packaging proteins, which control which genes are available for activation. The fusion proteins combine the ability of TAZ and YAP to control gene activity and the ability of CAMTA1 and TFE3 to make DNA more accessible, allowing the fusion proteins to drive uncontrolled cancerous growth. Similar TAZ and YAP fusion proteins have been found in other cancers, which can activate genes and potentially alter DNA packaging. Targeting drug development efforts at the proteins that complex with TAZ and YAP fusion proteins may lead to new therapies.

Utility of FISH in the diagnosis of angiomatoid fibrous histiocytoma: a series of 18 cases.

Angiomatoid fibrous histiocytoma is a mesenchymal neoplasm of intermediate malignancy and uncertain histogenesis/line of differentiation, which occurs most commonly in the extremities of children to young adults. It has a characteristic appearance characterized by a proliferation of histiocytoid cells with a lymphoid cuff and fibrous pseudocapsule, simulating the appearance of a neoplasm occurring within a lymph node. However, these classic histological features are not always present. Given the variable appearance of the neoplastic cells and the lack of consistently positive immunohistochemical markers, diagnosis can be problematic. Angiomatoid fibrous histiocytoma has been found to harbor three related translocations, a t(12;16)(q13;p11) resulting in a FUS/ATF1 fusion gene, t(12;22)(q13;q12) resulting in a EWSR1/ATF1 fusion, and t(2;22)(q33;q12) resulting in a EWSR1/CREB1 fusion. Fluorescence in situ hybridization (FISH) probes to EWSR1 and FUS, in theory, should detect all three translocations/gene fusions. We evaluated 18 cases of angiomatoid fibrous histiocytoma for rearrangements of EWSR1 and FUS by FISH, the largest series to date. We found that 13 of 17 (76%) cases of angiomatoid fibrous histiocytoma harbored rearrangements of EWSR1; rearrangements of FUS were not detected in any of the cases. This study affirms that the rearrangement of EWSR1 is a common genetic event in angiomatoid fibrous histiocytoma, and is thus useful diagnostically. This study supports the fact that the rearrangement of FUS is present in only a small minority of angiomatoid fibrous histiocytomas. Interestingly, 24% of the cases were translocation negative, and did not contain rearrangements of EWSR1 or FUS by FISH. Although it is possible that these cases contained cryptic rearrangements of EWSR1 or FUS that were not detectable by our FISH probes, it also raises the possibility that another translocation/gene fusion may be present in angiomatoid fibrous histiocytoma. Finally, we discuss some of the potential pitfalls of this technique, including confusion with other mesenchymal neoplasms containing rearrangement of EWSR1, in particular Ewing's sarcoma/PNET.

Solitary adult orbital myofibroma: Report of a case and review of the literature.

PURPOSE: Myofibromas are benign soft tissue tumors commonly encountered in infancy and childhood. Developing usually within the first two years of life, they can be multicentric and involve deep visceral organs. OBSERVATIONS: We present the rare occurrence of a solitary orbital myofibroma in an adult patient. The clinical, histopathologic and immunohistochemical findings of the tumor are documented. CONCLUSIONS: A comprehensive review of pediatric and adult orbital and periocular involvement by myofibroma is presented. Its characteristic pathologic and molecular findings are reviewed. IMPORTANCE: Myofibromas are uncommon but important tumors that can occur in the head and neck region, including the orbit. Seen more often in children, they can rarely be encountered in adult patients. Diagnosis is possible with a panel of immunostains and molecular analysis can be further confirmatory.

RABL6A Is an Essential Driver of MPNSTs that Negatively Regulates the RB1 Pathway and Sensitizes Tumor Cells to CDK4/6 Inhibitors.

PURPOSE: Malignant peripheral nerve sheath tumors (MPNST) are deadly sarcomas that lack effective therapies. In most MPNSTs, the retinoblastoma (RB1) tumor suppressor is disabled by hyperactivation of cyclin-dependent kinases (CDK), commonly through loss of CDK-inhibitory proteins such as p27(Kip1). RABL6A is an inhibitor of RB1 whose role in MPNSTs is unknown. To gain insight into MPNST development and establish new treatment options, we investigated RABL6A-RB1 signaling and CDK inhibitor-based therapy in MPNSTs. EXPERIMENTAL DESIGN: We examined patient-matched MPNSTs and precursor lesions by RNA sequencing (RNA-Seq) and IHC. Molecular and biological effects of silencing RABL6A and/or p27 in MPNST lines and normal human Schwann cells were determined. Tumor-suppressive effects of CDK inhibitors were measured in MPNST cells and orthotopic tumors. RESULTS: RABL6A was dramatically upregulated in human MPNSTs compared with precursor lesions, which correlated inversely with p27 levels. Silencing RABL6A caused MPNST cell death and G1 arrest that coincided with p27 upregulation, CDK downregulation, and RB1 activation. The growth-suppressive effects of RABL6A loss, and its regulation of RB1, were largely rescued by p27 depletion. Importantly, reactivation of RB1 using a CDK4/6 inhibitor (palbociclib) killed MPNST cells in vitro in an RABL6A-dependent manner and suppressed MPNST growth in vivo. Low-dose combination of drugs targeting multiple RB1 kinases (CDK4/6, CDK2) had enhanced antitumorigenic activity associated with potential MPNST cell redifferentiation. CONCLUSIONS: RABL6A is a new driver of MPNST pathogenesis that acts in part through p27-RB1 inactivation. Our results suggest RB1 targeted therapy with multiple pathway drugs may effectively treat MPNSTs.

Pseudosarcomatous fibroblastic/myofibroblastic proliferation in perinephric adipose tissue adjacent to renal cell carcinoma: a lesion mimicking well-differentiated liposarcoma.

Cytologically atypical stromal cells were found in the perinephric adipose tissue, mimicking well-differentiated liposarcoma in 12 of 59 (20%) consecutive nephrectomy specimens that were resected for renal cell carcinoma. Morphologically, the atypical cells included enlarged, hyperchromatic spindle cells and floret-type multinucleate cells. Of 59, 10 (17%) renal cell carcinomas invaded through the renal capsule into the perinephric adipose tissue. Of these cases, three (30%) contained the aforementioned atypical cells. In contrast, 9 of 49 cases without extrarenal invasion (18%) contained the atypical stromal cells. Of the 12 cases with atypical stromal cells, 3 (25%) were associated with extrarenal involvement. The atypical spindle cells exhibited focal to variable positivity for smooth muscle actin and desmin in 3 of the 14 cases (including two cases from our consultation files) each. Cytokeratin AE1/AE3, cytokeratin Cam 5.2, cytokeratin 7, epithelial membrane antigen, and S-100 were negative in all cases. Amplification of MDM2 gene region, which is commonly observed in well-differentiated liposarcoma, was absent by fluorescence in situ hybridization (FISH) in the atypical stromal cells. Immunohistochemistry and FISH suggest that the atypical cells are most consistent with reactive fibroblasts/myofibroblasts. Recognition of these atypical fibroblasts/myofibroblasts may help in avoiding the potential pitfall of misdiagnosing them as well-differentiated liposarcoma.

Fluorescence in situ hybridization in the diagnosis of soft tissue neoplasms: a review.

This paper presents an overview of the role of fluorescence in situ hybridization (FISH) in the diagnosis of soft tissue neoplasms. Many soft tissue neoplasms harbor characteristic translocations or amplification of gene regions, which can be assessed by FISH, and can be used to assist in their diagnosis. We discuss the major morphologic categories in which FISH has come to be used including high-grade round cell sarcomas, spindle cell sarcomas, low-grade myxoid neoplasms, adipocytic neoplasms, and malignant melanocytic neoplasms on the basis of a recent review of soft tissue neoplasms which were analyzed by FISH. We also review the molecular alterations (translocations and amplification of gene regions), which have come to define many of these diagnostic entities and the most effective way to evaluate them with FISH with attention to potential pitfalls. Finally, we discuss the advantages and disadvantages of FISH as a technique when appraising soft tissue neoplasms.

Desmoplastic Small Round Cell Tumors With Atypical Presentations: A Report of 34 Cases.

OBJECTIVES: Desmoplastic small round cell tumor (DSRCT) is an aggressive round cell sarcoma that arises in the abdominal cavity/pelvis of young males. We sought to expand its clinicopathologic spectrum. METHODS: Cases of DSRCT presenting in patients >30 years of age or tumors arising outside of the abdominal cavity/pelvis were retrieved. RESULTS: Thirty-four cases were identified. Sixteen tumors arose at atypical sites (head/neck, intracranial, thigh, axilla/shoulder, inguinal/paratesticular, intraosseous, and uterine corpus). The remaining 18 patients were older than 30 years, and their tumors involved the abdomen or pelvis. The majority of cases showed areas with classic histology, while 6 cases exhibited solid growth and 5 showed macronodular architecture. Cytologic appearance included round cell, rhabdoid, epithelioid, and small cell. CONCLUSION: DSRCT may arise at nonabdominal locations in both pediatric and adult populations, as well as intra-abdominally in older adults, and these tumors exhibit high rates of metastasis and morbidity.