MDM2 Amplified Sarcomas: A Literature Review

Murine Double Minute Clone 2, located at 12q15, is an oncogene that codes for an oncoprotein of which the association with p53 was discovered 30 years ago. The most important function of MDM2 is to control p53 activity; it is in fact the best documented negative regulator of p53. Mutations of the tumor suppressor gene p53 represent the most frequent genetic change in human cancers. By overexpressing MDM2, cancer cells have another means to block p53. The sarcomas in which MDM2 amplification is a hallmark are well-differentiated liposarcoma/atypical lipomatous tumor, dedifferentiated liposarcoma, intimal sarcoma, and low-grade osteosarcoma. The purpose of this review is to summarize the typical clinical, histopathological, immunohistochemical, and genetic features of these tumors.

Detailed histological analysis of a thrombectomy-resistant ischemic stroke thrombus: a case report

Background

Mechanical removal of a thrombus by thrombectomy can be quite challenging. For reasons that are not fully understood, some thrombi require multiple passes to achieve successful recanalization, whereas other thrombi are efficiently removed in a single pass. Since first pass success is associated with better clinical outcome, it is important to better understand the nature of thrombectomy resistant thrombi. The aim of this study was therefore to characterize the cellular and molecular composition of a thrombus that was very hard to retrieve via mechanical thrombectomy.

Case presentation

In a patient that was admitted with a right middle cerebral artery M1-occlusion, 11 attempts using various thrombectomy devices and techniques were required for removal of the thrombus. This peculiar case provided a rare opportunity to perform an in-depth histopathological study of a difficult to retrieve thrombus. Thrombus material was histologically analyzed using hematoxylin and eosin, Martius Scarlet Blue stain (red blood cells and fibrin), Feulgen stain (DNA), von Kossa stain (calcifications) and immunohistochemical analysis of von Willebrand factor, platelets, leukocytes and neutrophil extracellular traps. Histological analysis revealed abnormally high amounts of extracellular DNA, leukocytes, von Willebrand factor and calcifications. Extracellular DNA stained positive for markers of leukocytes and NETs, suggesting that a significant portion of DNA is derived from neutrophil extracellular traps.

Conclusion

In this unique case of a nearly thrombectomy-resistant stroke thrombus, our study showed an atypical composition compared to the common structural features found in ischemic stroke thrombi. The core of the retrieved thrombus consisted of extracellular DNA that colocalized with von Willebrand factor and microcalcifications. These results support the hypothesis that von Willebrand factor, neutrophil extracellular traps and microcalcifications contribute to mechanical thrombectomy resistance. Such information is important to identify novel targets in order to optimize technical treatment protocols and techniques to increase first pass success rates.

Intraosseous schwannoma of the glenoid: case report and literature review

Intraosseous schwannomas represent an extremely rare subgroup of schwannomas, accounting for <1% of all primary bone tumors. They mostly occur in the mandible, the maxilla, the sacrum, and they are also seen in long bones. We herein report a rare presentation of an intraosseous schwannoma in the glenoid of a 49-year-old patient. She complained of shoulder pain and was referred to the orthopaedic oncologist after detection of a suspicious lesion on imaging. Biopsy revealed benign spindle cells and immunohistochemistry was positive for S100. Because of the rarity of these intraosseous schwannomas it is important to recognize their radiological and histological features and make a differential diagnosis with other lytic tumors. Only if these characteristics are recognized, correct treatment can be given with definite curettage and bone grafting and correct follow-up with avoidance of unnecessary adjuvant therapy.

Comprehensive targeted next-generation sequencing approach in the molecular diagnosis of gastrointestinal stromal tumor

Mutational analysis guides therapeutic decision making in patients with advanced-stage gastrointestinal stromal tumors (GISTs). We evaluated three targeted next-generation sequencing (NGS) assays, consecutively used over 4 years in our laboratory for mutational analysis of 162 primary GISTs: Agilent GIST MASTR, Illumina TruSight 26 and an in-house developed 96 gene panels. In addition, we investigated the feasibility of a more comprehensive approach by adding targeted RNA sequencing (Archer FusionPlex, 11 genes) in an attempt to reduce the number of Wild Type GISTs. We found KIT or PDGFRA mutations in 149 out of 162 GISTs (92.0%). Challenging KIT exon 11 alterations were initially missed by different assays in seven GISTs and typically represented deletions at the KIT intron 10-exon 11 boundary or large insertions/deletions (>24 base pairs). Comprehensive analysis led to the additional identification of driver alterations in 8/162 GISTs (4.9%): apart from BRAF and SDHA mutations (one case each), we found five GISTs harboring somatic neurofibromatosis type 1 (NF1) alterations (3.1%) and one case with an in-frame TRIM4-BRAF fusion not reported in GIST before. Eventually, no driver alteration was found in two out of 162 GISTs (1.2%) and three samples (1.9%) failed analysis. Our study shows that a comprehensive targeted NGS approach is feasible for routine mutational analysis of GIST, thereby substantially reducing the number of Wild Type GISTs, and highlights the need to optimize assays for challenging KIT exon 11 alterations.

RARE-56. PERITONEAL SEEDING OF A DIFFUSE LEPTOMENINGEAL GLIONEURONAL TUMOR IN A CHILD

Diffuse leptomeningeal glioneuronal tumors (DLGNT) are rare neoplasms of the central nervous system and have been included in the 2016 update of the WHO classification. This is the first description of a DLGNT disseminating to the peritoneal cavity via a ventriculoperitoneal shunt (VPS) in a child. We describe an 11-year old girl who received a VPS for a Dandy-Walker malformation at the age of seven, and was diagnosed with a spinal pilocytic astrocytoma with leptomeningeal metastases six months later. She received chemotherapy (SIOP-LGG protocol) with partial response, and had progressive disease eight months after therapy cessation. Following a novel biopsy, the diagnosis was revised to a DLGNT, with a KIAA1549-BRAF fusion and loss of 1p. She received vinblastine, but was clinically progressive and craniospinal radiotherapy was initiated. 13 months later, she suddenly presented with ascites. The inferior vena cava was compressed due to the ascites, and an abdominal drain was placed, with massive fluid release. Abdominal MRI indicated an omental cake and peritoneal contrast enhancement. Bone metastases were suspected in the iliac and femoral bones. Anatomopathological examination of the ascites showed an atypical cell population, with irregular, hyperchromatic and enlarged nuclei resembling the primary tumor. The cells were positive for synaptophysin, MAP2 and weakly positive for S100. Pan-NTRK staining was negative. The diagnosis of a metastatic localization of the DLGNT was made, due to seeding of tumoral cells via the VPS. Treatment with a MEK-inhibitor was initiated, but was stopped due to progressive disease and she died 3 weeks later.

Abstract 1676: Plocabulin, a novel tubulin inhibitor, has antitumor activity in various patient-derived xenograft models of soft tissue sarcoma

Objective: Soft tissue sarcomas (STS) constitute a heterogeneous group of rare, malignant tumors arising in mesenchymal tissue. Doxorubicin (DOX)-based chemotherapy has been the standard of care for patients with advanced and metastatic STS, despite providing low response rates and poor disease control in this disease. Even for patients who respond to treatment, the outcome of advanced and metastatic STS is poor. In light of this, there is a clear need for more effective and novel therapeutic compounds for STS. In the current study, we explored the activity of plocabulin (PLO; PM060184, PharmaMar), a novel cytotoxic tubulin-dynamics modifier, in patient-derived xenograft (PDX) models of some common and some rare histologic subtypes of STS.

Methods: Female NMRI nu/nu mice (n=80) were transplanted bilaterally with human STS xenografts: UZLX-STS134CRS (CIC-rearranged sarcoma), UZLX-STS124DDLPS (dedifferentiated liposarcoma), UZLX-STS22_2FLMS (leiomyosarcoma) and UZLX-STS122FIS (intimal sarcoma). Xenografted animals were randomly assigned to three treatment groups: 1) vehicle (20% hydroxypropyl β-cyclodextrin) 6.4 ml/kg intravenously (i.v.) once weekly (QW), 2) DOX 3.0 mg/kg i.v. QW, or 3) PLO 16 mg/kg i.v. QW. All treatments lasted 22 days. Antitumor activity was assessed by tumor volume analysis, histopathology and Western blotting. Mitotic count, phospho-histone H3 and Ki-67 were analyzed for proliferative activity. Apoptotic count, and cleaved poly-(ADP-ribose)-polymerase were analyzed for apoptotic activity. CD31 immunostains were used to evaluate the tumor vasculature. The Kruskal-Wallis test with Dunn's multiple comparisons (DMC) test was used to compare non-parametric variables between groups. Statistical significance was defined as p &lt;0.05.

Results: PLO treatment resulted in tumor shrinkage in UZLX-STS134CRS (to 40% of baseline volume) and UZLX-STS22_2FLMS (to 27%), and tumor volume stabilization in UZLX-STS124DDLPS and UZLX-STS122FIS. Vehicle-treated tumors of UZLX-STS134CRS, UZLX-STS22_2FLMS and UZLX-STS124DDLPS reached 363%, 287% and 261% of baseline volume, respectively. DOX did not affect tumor volume. All DOX-treated mice of UZLX-STS122FIS were lost before the end of the experiment: one mouse was sacrificed on day 16 due to body weight loss, the remaining five were found dead on day 19. Despite this, relative tumor volumes already differed significantly between the vehicle-PLO and DOX-PLO groups on day 16 for this model (p&lt;0.001 and p=0.002, respectively, DMC). PLO-treated tumors of UZLX-STS134CRS and UZLX-STS22_2FLMS were necrotic and degenerated to such an extent that histological analysis could not be performed in full. In the PLO-treated tumors of UZLX-STS122FIS, we demonstrated a significant decrease in the total vascular area, consistent with the drug's vascular disrupting capacity. No effects on proliferation or apoptosis were observed. The experimental drug was well tolerated throughout the experiment at the administered dose.

Conclusion: PLO is a novel anti-tubulin agent showing potent antitumor activity in a variety of PDX modes of STS. The drug induces cytotoxicity mainly through necrosis and is more active than DOX. This study provides strong arguments to study PLO further in STS and to explore the compound in clinical trials involving mesenchymal malignancies.

Citation Format: Yannick Wang, Agnieszka Wozniak, Jasmien Cornillie, Che-Jui Lee, María José Guillén, Pablo Avilés, Maria Debiec-Rychter, Raf Sciot, Patrick Schöffski. Plocabulin, a novel tubulin inhibitor, has antitumor activity in various patient-derived xenograft models of soft tissue sarcoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1676.

Abstract 5438: Establishment of an academic tissue microarray platform as an efficient tool for soft tissue sarcoma research

Objective: Soft tissue sarcoma (STS) is a rare and heterogeneous family of mesenchymal tumors, characterized by morphological and genetic diversity. Histopathology and molecular profiling is used in both clinical routine and in sarcoma research, then primarily relying on the availability of archival material. Tissue microarrays (TMAs) from sarcoma tissue blocks have potential advantages over conventional tissue analysis from individual patients in terms of efficiency and cost-effectiveness. Since 2015 we have built TMAs in the Laboratory of Experimental Oncology at KU Leuven (Leuven, Belgium), using left-over archival material available from STS patients.

Methods: For the TMA construction, donor blocks were selected according to the following criteria: blocks with sufficient tumor tissue and height at least 3 mm from STS patients diagnosed at the University Hospitals Leuven, Leuven, Belgium; Leiden University Medical Center, Leiden, The Netherlands and University Hospital Zürich, Zürich, Switzerland, as well as STS patients enrolled in EORTC phase 2 trial 90101 “CREATE”. Cases included in the TMAs are well annotated in terms of pathological diagnosis, treatment and clinical follow-up. Each TMA block contains duplicate or triplicate 1.0-1.5 mm tissue cores from representative areas selected by reference sarcoma pathologists. The construction of TMAs was performed with TMA Grand Master (3DHistech) at the Translational Research Unit at University of Bern, Switzerland or in Leiden, The Netherlands.

Result: At present we have created TMAs from the following STS subtypes: clear cell sarcoma (CCSA, 22 and 32 cases per TMA block), alveolar soft part sarcoma (ASPS, 12 and 47), inflammatory myofibroblastic tumor (IMFT, 12 and 21), alveolar rhabdomyosarcoma (24) and leiomyosarcoma (55). For CCSA, ASPS and IMFT we have separate TMAs from local clinical cases and from EORTC 90101 “CREATE”. For drug- and target-screening purposes in a broader range of STS we also made TMAs representing multiple, most common subtypes: angiosarcoma, dedifferentiated, pleomorphic and myxoid liposarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumor, myxofibrosarcoma, rhabdomyosarcoma, synovial sarcoma and undifferentiated pleomorphic sarcoma, with 7-11 individual cases per tumor type. TMA construction is still ongoing in other relevant sarcoma subtypes.

Conclusion: We have built and are currently expanding a ready to use TMA platform representing the broad heterogeneity of STS. TMAs are available for rapid and cost-effective morphological, immunohistochemical and molecular characterization and identification of novel diagnostic markers as well as drug targets. The platform is readily available to academic partners for collaboration.

Citation Format: Che-Jui Lee, Agnieszka Wozniak, Thomas van Cann, Jasmien Wellens, Inti Zlobec, Britschgi Christian, Judith V.M.G Bovée, Raf Sciot, Patrick Schöffski. Establishment of an academic tissue microarray platform as an efficient tool for soft tissue sarcoma research [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5438.

Abstract 794: Molecular analysis of archival inflammatory myofibroblastic tumor tissue samples from EORTC 90101 “CREATE” and correlation with response to crizotinib

About 50% of inflammatory myofibroblastic tumors (IMFTs) harbor rearrangements of anaplastic lymphoma kinase (ALK), the most common driver in this rare tumor. EORTC 90101 “CREATE” is so far the only prospective, disease-specific phase II clinical trial performed in IMFT. It showed high antitumor activity of crizotinib, an ALK/ROS1/MET-inhibitor. This activity was mainly seen in ALK-rearranged IMFT, but the trial results suggested that other molecular events may also contribute to crizotinib sensitivity. Here we present results of an in-depth molecular analysis of archival IMFTs collected from patients within the CREATE trial with the aim to identify other molecular alterations, which could be responsible for response to crizotinib. DNA from archival IMFTs (primary tumor or metastatic lesion) was used for low-coverage whole genome sequencing to identify genomic regions of gains or losses. Whole exome sequencing (WES) was used to assess the mutational landscape, and mutations affecting cancer consensus genes (CCGs) were analyzed in more detail. Correlative and statistical analysis were used to assess the association between molecular findings and clinical outcomes of IMFT patients. In 24 IMFTs analyzed, the recurrent whole-arm copy number losses were: 22q (58% of cases), 16p (33%), 16q (29%), 13q (29%), 19q (29%), 19p (25%), 6p (25%), 6q (21%) and 18q (21%). Loss of chromosome 19 was found to be associated with shorter progression-free survival in patients receiving crizotinib (p = 0.008). Moreover, 2p21 (including EPAS1, SIX2, EML4 from the CCG set) was frequently amplified (54% of cases), while recurrent losses were observed at 22q12.3 (71%, ISX), 7q36.3 (54%, MNX1), 10q26.3 (54%, MGMT, DUX4), 1p36.32 (50%, RPL22, SKI, TNFRSF14, CAMTA1, PRDM16), 8p23.3 (50%, ARHGEF10), 12q24.33 (46%, POLE), and 11q13.4 (33%, CCND1). No significant correlations were found between focal copy number alterations and crizotinib response. A complex genetic rearrangement involving chromosome 2, identified in 2 ALK-rearranged cases, was likely consistent with chromothripsis, a form of genomic instability related to cancer development. WES was performed in 22 cases with an average of 392 alterations per sample. When considering non-synonymous mutations in CCG, a total of 178 mutations were identified, affecting 143 genes with an average of 7 per case. Mutations in 30 CCGs, identified in ≥ 2 cases, were mainly related to DNA damage/repair mechanism, WNT, RB1-TP53, and RTK-RAS-PI3K signaling. In a case with no ALK rearrangement and ALK immunopositivity, a single base substitution in ALK (p.N571K) was identified. In conclusion, we identified multiple molecular alterations in archival IMFTs and provided further insight in the molecular profile of this ultra-rare malignancy, which may potentially lead to the identification of novel therapeutic targets for IMFT patients.

Citation Format: Che-Jui Lee, Patrick Schöffski, Elodie Modave, Bram Boeckx, Diether Lambrechts, Maria Debiec-Rychter, Raf Sciot, Jozef Sufliarsky, Hans Gelderblom, Jean-Yves Blay, Agnieszka Wozniak. Molecular analysis of archival inflammatory myofibroblastic tumor tissue samples from EORTC 90101 “CREATE” and correlation with response to crizotinib [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 794.

Abstract 1117: XenoSarc: Patient-derived xenograft (PDX) models of soft tissue sarcoma (STS) and their histopathological and molecular characterization

Background: STS constitutes a rare family of mesenchymal tumors with more than 70 subtypes classified by WHO (2013). The limited treatment options available for advanced STS underline the need for reliable preclinical models, especially from ultra-rare subtypes, to test novel therapeutic strategies.

Methods: A panel of PDX models was established by subcutaneous implantation of fresh tumor specimens in immunodeficient, athymic nude NMRI mice. Once tumor growth was observed, pieces of tumor were re-transplanted to next generations of mice. At each passage tumor fragments were collected for histopathological and molecular characterization. A model was considered “established” after observing stable histological and molecular features for at least two passages. Furthermore, ex-mouse tumor tissue samples were stored, further characterized by immunocytology and flow cytometry and cultured to be used for in vitro drug testing.

Results: Between September 2011 and November 2019, 375 STS samples from 325 consenting patients treated at the University Hospitals, Leuven, Belgium have been transplanted. A total of 56 PDX models were established, maintaining the histopathological and molecular features of the original tumor. Detailed clinical information about the donor patient and tumor characteristics (including sensitivity to standard and experimental agents), is known for every model.

At present the XenoSarc platform includes ready to use models of dedifferentiated liposarcoma (11 models), gastrointestinal stromal tumor (8), myxofibrosarcoma (8), leiomyosarcoma (7), malignant peripheral nerve sheath tumor (3), synovial sarcoma (2), pulmonary artery intimal sarcoma (2), epithelioid hemangioendothelioma (1), mesenchymal chondrosarcoma (1), pleomorphic rhabdomyosarcoma (1), CIC-rearranged round cell sarcoma (1), myxoinflammatory fibroblastic sarcoma (1), rhabdomyosarcoma not otherwise specified (NOS) (1), telangiectatic extraskeletal osteosarcoma (1), extraskeletal osteosarcoma (1) and high-grade undifferentiated pleomorphic sarcoma (7). These models are well-characterized, including molecular information on copy number changes (by low-coverage whole genome sequencing), gene expression profile (by RNA-Seq) and targeted sequencing to detect mutations in genes involved in tumorigenesis. In addition, we have constructed tissue microarrays (TMA) from the xenografts which are used for target identification and model selection for preclinical studies. We are using the xenografts for in vivo testing of novel agents, including targeted and cytotoxic (pro-)drugs, and results already served as rationale for a number of prospective clinical trials. A total of 27 other xenografts are still in early stages of engraftment, not yet fulfilling our criteria of an “established” model.

Conclusion: The XenoSarc platform offers a lot of opportunities for studying the biology of a variety of important sarcoma subtypes including ultra-rare entities, and has proven efficiency for early drug screening in STS in preparation of clinical testing of novel compounds. The platform is well maintained and continuously expanded, and available to collaborators from academia and industry.

Citation Format: Agnieszka Wozniak, Britt Van Renterghem, Jasmien Cornillie, Yannick Wang, Che-Jui Lee, Jasmien Wellens, Ulla Vanleeuw, Madita Nysen, Daphne Hompes, Friedl Sinnaeve, Hazem Wafa, Baki Topal, Tom Verbelen, Maria Debiec-Rychter, Raf Sciot, Patrick Schöffski. XenoSarc: Patient-derived xenograft (PDX) models of soft tissue sarcoma (STS) and their histopathological and molecular characterization [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1117.

Plocabulin, a novel tubulin inhibitor, has potent antitumor activity in patient-derived xenograft models of gastrointestinal stromal tumors

The majority of patients with gastrointestinal stromal tumors (GIST) eventually become resistant with time due to secondary mutations in the driver receptor tyrosine kinase. Novel treatments that do not target these receptors may therefore be preferable. For the first time, we evaluated a tubulin inhibitor, plocabulin, in patient-derived xenograft (PDX) models of GIST, a disease generally considered to be resistant to cytotoxic agents. Three PDX models of GIST with different KIT genotype were generated by implanting tumor fragments from patients directly into nude mice. We then used these well characterized models with distinct sensitivity to imatinib to evaluate the efficacy of the novel tubulin inhibitor. The efficacy of the drug was assessed by volumetric analysis of the tumors, histopathology, immunohistochemistry and Western blotting. Plocabulin treatment led to extensive necrosis in all three models and significant tumor shrinkage in two models. This histological response can be explained by the drug's vascular-disruptive properties, which resulted in a shutdown of tumor vasculature, reflected by a decreased total vascular area in the tumor tissue. Our results demonstrated the in vivo efficacy of the novel tubulin inhibitor plocabulin in PDX models of GIST and challenge the established view that GIST are resistant to cytotoxic agents in general and to tubulin inhibitors in particular. Our findings provide a convincing rationale for early clinical exploration of plocabulin in GIST and warrant further exploration of this class of drugs in the management of this common sarcoma subtype.

•

First study evaluating a tubulin inhibitor in patient-derived xenograft models of gastro-intestinal stromal tumors

•

Plocabulin, a novel tubulin inhibitor, has efficacy independant of KIT genotype

•

Plocabulin induced extensive, central tumor necrosis, mainly through its antiangiogenic properties.

•

Our results challenge the established view that gastro-intestinal stromal tumors are resistant to cytotoxic agents.

All that glitters is not prostate cancer: incidental finding of PSMA-avid meningioma

We present a case of a 79 year old patient with a medical history of unilateral nerve-sparing radical prostatectomy due to a pT3aN0 (Gleason score 7) prostate carcinoma. Because of slightly elevated prostate specific antigen (PSA) level (0.35ng/dL), a fluorine-18-prostate specific membrane antigen (¹⁸F-PSMA)-1007 positron emission tomography/computed tomography (PET/CT) scan was performed, showing no signs of malignant recurrence. However, a moderately PSMA-avid nodular lesion was observed in the left occipital region with homogeneous contrast enhancement, suggestive for a meningioma, which was confirmed on magnetic resonance imaging (MRI). One year later, the lesion was resected due to a small but significant growth. Histology confirmed the diagnosis of a transitional type meningioma (WHO grade 1).

Next generation sequencing for GNAS uncovers CD34 as a sensitive marker for intramuscular myxoma

BACKGROUND

Intramuscular myxoma is a soft tissue myxoid tumor with a broad morphological differential diagnosis and recent developments have led to the identification of markers that can exclude some, but not all, differential diagnostic entities. However, a sensitive confirmatory marker for intramuscular myxoma has not been clearly identified. Since there is some evidence that mutations in the GNAS gene could be such a marker, we evaluated our results of next-generation sequencing testing for GNAS mutations performed in recent years on our series of intramuscular myxoma.

MATERIALS AND METHODS

Next-generation sequencing was performed on 10 cases of intramuscular myxoma diagnosed between 2015 and 2019, using either the TruSight Tumor 26 panel or an in-house developed 97 cancer gene panel. Additionally, immunohistochemistry for CD34 was performed on all cases.

RESULTS

All intramuscular myxomas showed a diffuse and strong expression of CD34 and a GNAS mutation was found in 88% of cases, making this a very sensitive positive test for the diagnosis of intramuscular myxoma.

CONCLUSIONS

Under the condition that contemporary next-generation sequencing is applied as testing method, searching for GNAS mutations is a very sensitive confirmatory test for the diagnosis of intramuscular myxoma, obviating the necessity to perform tests that exclude other entities by the virtue of their negative result. The molecular tests results also identified strong and diffuse CD34 expression as a sensitive, albeit non-specific, marker for intramuscular myxoma.

XenoSarc: A comprehensive platform of patient-derived xenograft (PDX) models of soft tissue sarcoma (STS) for early drug testing

37

Background: STS is a family of rare, heterogeneous tumors with > 70 subtypes. There is an urgent need for reliable preclinical models, especially for orphan subtypes of STS, given the limited treatment options. Methods: A panel of PDX models was established by s.c. implantation of fresh tumor specimens in athymic NMRI mice. Growing pieces of tumor were re-transplanted to next generations of mice. At each passage fragments were collected for histological/molecular characterization. A model was considered “established” after observing stable features for at least 2 passages. Ex-mouse tissue samples were stored, characterized by immunohistochemistry/flow cytometry and used for in vitro drug testing. Results: Between 2011-2019, 329 samples from 301 consenting patients were transplanted; 56 models are established, 16 additional models are in early passaging. Clinical information about donor and tumor (including sensitivity to standard and experimental agents) is available. The platform includes models of dedifferentiated lipo- (10 models), myxofibro- (8), leiomyo- (7), synovial (2), intimal (2), CIC-positive round cell (1), mesenchymal chondro- (1), extraskeletal osteo- (1), myxoid lipo- (1), myxoinflammatory fibroblastic (1), rhabdomyo- (2) and high-grade undifferentiated pleomorphic sarcoma (7), as well as GIST (8), MPNST (4) and epithelioid hemangioendothelioma (1). Models are well-characterized, with molecular information on copy number changes (low-coverage whole genome sequencing) and gene expression profile (RNA-Seq) available. We also constructed tissue microarrays from the xenografts which are used for target identification and model selection for preclinical studies. Xenografts are available for in vivo testing of novel agents, and results already served as a rationale for a number of prospective clinical trials. Conclusions: XenoSarc offers opportunities for studying the biology of a variety of sarcoma subtypes including ultra-rare entities and is a valuable tool for early drug screening in preparation of clinical STS trials. The platform is well maintained and continuously expanded, and available to collaborators from academia and industry.

Establishment of a tissue microarray (TMA) platform as an efficient tool for soft tissue sarcoma (STS) research available for collaboration

38

Background: STS is a very heterogeneous family of orphan malignancies, characterized by morphological and genetic diversity. Tissue samples from individual STS patients are commonly used for routine diagnostic and research purposes. TMAs from multiple sarcoma tissue blocks have potential advantages over conventional tissue analysis in terms of efficiency and cost-effectiveness. We have established a comprehensive sarcoma TMA research platform. Methods: TMAs were constructed using left-over tissue from STS patients diagnosed at University Hospitals Leuven (B), Leiden University Medical Center (NL) and University Hospital Zürich (CH), and from patients with orphan sarcomas enrolled in EORTC trial 90101 “CREATE”. The clinical cases are well annotated in terms of diagnosis, treatment and follow-up. Each TMA block contains duplicate/triplicate 1.0-1.5 mm tissue cores from representative areas selected by sarcoma pathologists. The construction of TMAs was performed using TMA Grand Master (3DHistech) at University of Bern (CH) and in Leiden (NL). Results: The following subtype-specific TMAs have been created: clear cell sarcoma (CCSA, 54 cases), alveolar soft part sarcoma (ASPS, 59), inflammatory myofibroblastic tumor (IMFT, 33), alveolar rhabdomyo- (24) and leiomyosarcoma (55). For CCSA, ASPS and IMFT we have matching TMAs from clinical routine and patients entered in EORTC 90101. As a tool for broader drug- and target-screening purposes in STS we also produced a multi-sarcoma TMA combining multiple, more common subtypes on one block: angio-, dedifferentiated, pleomorphic and myxoid lipo-, leiomyo-, myxofibro-, rhabdomyo-, synovial and undifferentiated pleomorphic sarcoma, and MPNST, with 7-11 individual cases per tumor type. TMA construction is ongoing in other relevant sarcoma subtypes. Conclusions: We are currently expanding a very useful TMA platform representing the broad heterogeneity of STS, from more common to ultra-rare variants. TMAs are available for rapid, cost-effective morphological, histochemical and molecular characterization and identification of novel drug targets in collaboration with academic and commercial partners.

Assessment of the platelet-derived growth factor receptor alpha antibody olaratumab in a panel of patient-derived soft tissue sarcoma xenografts

Background

Soft tissue sarcoma (STS) comprises a family of rare, heterogeneous tumors of mesenchymal origin. Single-agent doxorubicin remains the first-line standard-of-care treatment for advanced and inoperable STS, but response rates are only around 15%. In 2016, phase Ib/II clinical trial results reported an overall survival benefit of 11.8 months when combining doxorubicin and the platelet-derived growth factor receptor alpha (PDGFRA)-directed antibody olaratumab compared to doxorubicin alone, without providing a scientific rationale for such unprecedented therapeutic effect. We decided to evaluate the efficacy of olaratumab in a panel of STS patient-derived xenografts (PDX).

Methods

NMRI nu/nu mice were bilaterally transplanted with tumor tissue of patient-derived xenograft models expressing PDGFRA, including models of leiomyosarcoma (UZLX-STS22), malignant peripheral nerve sheath tumor (UZLX-STS39), myxofibrosarcoma (UZLX-STS59) and undifferentiated pleomorphic sarcoma (UZLX-STS84). Mice were randomly divided into four different treatment groups: (1) control, (2) doxorubicin (3 mg/kg once weekly), (3) anti-PDGFRA [olaratumab (60 mg/kg twice weekly) + mouse anti-PDGFRA antibody 1E10 (20 mg/kg twice weekly)] and (4) the combination of doxorubicin and anti-PDGFRA (same dose/schedule as in the single treatment arms). Tumor volume, histopathology and Western blotting were used to assess treatment efficacy.

Results

Anti-PDGFRA treatment as a single agent did not reduce tumor growth and did not result in significant anti-proliferative or pro-apoptotic activity. Combining doxorubicin and anti-PDGFRA did not reduce tumor burden, though a mild inhibition of proliferation was observed in UZLX-STS39 and -STS59. A pro-apoptotic effect was observed in all models except UZLX-STS22. Antitumor effects on histology were not significantly different comparing doxorubicin and the combination treatment. Moreover, anti-PDGFRA treatment, both as a single agent as well as combined with doxorubicin, did not result in inhibition of the downstream MAPK and PI3K/AKT signaling pathways.

Conclusions

We were not able to demonstrate significant antitumor effects of anti-PDGFRA treatment in selected STS PDX models, neither alone nor in combination with doxorubicin. This is in line with the very recent results of the phase III clinical trial NCT02451943 ANNOUNCE, which did not confirm the clinical benefit of olaratumab in combination with doxorubicin over single agent doxorubicin.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5872-1) contains supplementary material, which is available to authorized users.

Neurofibromatosis type 1-related pseudarthrosis: Beyond the pseudarthrosis site

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder affecting approximately 1 in 2,000 newborns. Up to 5% of NF1 patients suffer from pseudarthrosis of a long bone (NF1-PA). Current treatments are often unsatisfactory, potentially leading to amputation. To gain more insight into the pathogenesis we cultured cells from PA tissue and normal-appearing periosteum of the affected bone for NF1 mutation analysis. PA cells were available from 13 individuals with NF1. Biallelic NF1 inactivation was identified in all investigated PA cells obtained during the first surgery. Three of five cases sampled during a later intervention showed biallelic NF1 inactivation. Also, in three individuals, we examined periosteum-derived cells from normal-appearing periosteum proximal and distal to the PA. We identified the same biallelic NF1 inactivation in the periosteal cells outside the PA region. These results indicate that NF1 inactivation is required but not sufficient for the development of NF1-PA. We observed that late-onset NF1-PA occurs and is not always preceded by congenital bowing. Furthermore, the failure to identify biallelic inactivation in two of five later interventions and one reintervention with a known somatic mutation indicates that NF1-PA can persist after the removal of most NF1 negative cells.

Clinical presentation, natural history and therapeutic approach in patients with solitary fibrous tumor: A retrospective analysis

e22522

Background: Solitary fibrous tumor (SFT), a rare variant of soft tissue sarcoma (STS), is characterized by the presence of a NAB2-STAT6 fusion. Given the orphan character of SFT we performed a retrospective analysis. Methods: We retrospectively reviewed all patients (pts) with SFT treated in our institution between 12/1990 - 09/2017. Results: We identified 94 SFT pts (incl. hemangiopericytoma) with a med. follow-up for 4.7 yrs. Common anatomic sites were chest (33%), abdomen (21.3%), brain (12.8%) and extremities (9.6%). The symptomatology at diagnosis was variable. Only 6.4% presented with synchronous metastasis. Hypoglycemia (Doege-Potter syndrome) was seen in 2.1% of cases. A resection of the primary SFT was done in 86 pts (91.5%), their disease-free survival was 35.5 mo and 43% stayed SFT-free during follow-up. Local recurrence occurred in 26.7% of cases, associated with a med. overall survival (OS) of 45.1 mo. Metachronous metastasis was seen in 30.2% of pts, occurring after a med. follow-up of 36 mo. Med. OS after diagnosis of metastasis was 19.0 mo. Systemic therapy was given to 92.9% of pts with inoperable/metastatic disease. The most common 1st line therapy was doxorubicin single agent (57.7% of pts), achieving responses in 13.3% of pts. 2nd line therapies included ifosfamide and pazopanib (31.3% of pts each), 3rd line treatment was very heterogeneous. Conclusions: SFT is an orphan malignancy with a variable clinical course, low incidence of distant spread at first diagnosis but considerable risk of local failure and metachronous metastasis. Surgery is the only curative option at diagnosis, time of relapse and in case of resectable metastasis. Palliative systemic therapy is considered in pts with inoperable/metastatic disease but achieves low response rates. The natural course and survival outcomes of SFT cases treated with palliative intent tend to be better than in non-selected STS pts.

No relevant activity of olaratumab in patient-derived soft tissue sarcoma xenografts selected for expression of platelet-derived growth factor receptor a

e22556

Background: Soft tissue sarcoma (STS) comprises a heterogeneous family of rare tumors of mesenchymal origin. Single-agent doxorubicin (DOX) remains the standard-of-care for advanced and inoperable STS, but response rates are < 15% and survival is generally poor. In 2016, Tap et al. reported impressive results of a phase Ib/II trial combining DOX and the platelet-derived growth factor receptor a (PDGFRA)-directed antibody olaratumab (OLA), suggesting an unprecedented survival advantage of the combination over DOX alone, without providing a mechanistic rationale for the observed activity (Lancet 2016;388:488-97). We decided to evaluate the efficacy of OLA in a panel of patient-derived STS xenografts (PDX). Methods: NMRI nu/nu mice were transplanted bilaterally with tumor tissue of models expressing PDGFRA, including PDX of leiomyosarcoma (UZLX-STS22), malignant peripheral nerve sheath tumor (STS39), myxofibrosarcoma (STS59) and undifferentiated pleomorphic sarcoma (STS84). Mice were randomly divided into 4 treatment groups: (1) control, (2) DOX (3 mg/kg once weekly), (3) anti-PDGFRA [OLA (60 mg/kg twice weekly) + mouse anti-PDGFRA antibody 1E10 (20 mg/kg twice weekly)] and (4) the combination of DOX and anti-PDGFRA (same dose/schedule as single treatment arms). Tumor volume, histopathology and Western blotting were used to assess treatment efficacy. Results: Anti-PDGFRA treatment as single agent did not reduce tumor growth and did not result in significant anti-proliferative or pro-apoptotic activity. Combining DOX and anti-PDGFRA did not reduce tumor burden, though a mild inhibition of proliferation was observed in models STS39 and STS59 and a pro-apoptotic effect was seen in all models except STS22. Antitumor effects on histology were not significantly different comparing DOX and the combination treatment. Anti-PDGFRA treatment, both as a single agent as well as with DOX, did not inhibit downstream MAPK and PI3K/AKT signaling pathways. Conclusions: In vivo findings in PDX models selected for PDGFRA expression support negative findings of the phase III trial NCT02451943 with OLA reported at this meeting.

Activity and safety of crizotinib in patients with alveolar soft part sarcoma with rearrangement of TFE3: European Organization for Research and Treatment of Cancer (EORTC) phase II trial 90101 'CREATE'

Background

Alveolar soft part sarcoma (ASPS) is an orphan malignancy associated with a rearrangement of transcription factor E3 (TFE3), leading to abnormal MET gene expression. We prospectively assessed the efficacy and safety of the MET tyrosine kinase inhibitor crizotinib in patients with advanced or metastatic ASPS.

Patients and methods

Eligible patients with reference pathology-confirmed ASPS received oral crizotinib 250 mg bd. By assessing the presence or absence of a TFE3 rearrangement, patients were attributed to MET+ and MET- sub-cohorts. The primary end point was the objective response rate (ORR) according to local investigator. Secondary end points included duration of response, disease control rate (DCR), progression-free survival (PFS), progression-free rate, overall survival (OS) and safety.

Results

Among 53 consenting patients, all had a centrally confirmed ASPS and 48 were treated. A total of 45 were eligible, treated and assessable. Among 40 MET+ patients, 1 achieved a confirmed partial response (PR) that lasted 215 days and 35 had stable disease (SD) as best response (ORR: 2.5%, 95% CI 0.6% to 80.6%). Further efficacy end points in MET+ cases were DCR: 90.0% (95% CI 76.3% to 97.2%), 1-year PFS rate: 37.5% (95% CI 22.9% to 52.1%) and 1-year OS rate: 97.4% (95% CI 82.8% to 99.6%). Among 4 MET- patients, 1 achieved a PR that lasted 801 days and 3 had SD (ORR: 25.0%, 95% CI 0.6% to 80.6%) for a DCR of 100% (95% CI 39.8% to 100.0%). The 1-year PFS rate in MET- cases was 50% (95% CI 5.8% to 84.5%) and the 1-year OS rate was 75% (95% CI 12.8% to 96.1%). One patient with unknown MET status due to technical failure achieved SD but stopped treatment due to progression after 17 cycles. The most common crizotinib-related adverse events were nausea [34/48 (70.8%)], vomiting [22/48 (45.8%)], blurred vision [22/48 (45.8%)], diarrhoea (20/48 (41.7%)] and fatigue [19/48 (39.6%)].

Conclusion

According to European Organization for Research and Treatment of Cancer (EORTC) efficacy criteria for soft tissue sarcoma, our study demonstrated that crizotinib has activity in TFE3 rearranged ASPS MET+ patients.

Clinical trial number

EORTC 90101, NCT01524926.

Establishment and Characterization of Histologically and Molecularly Stable Soft-tissue Sarcoma Xenograft Models for Biological Studies and Preclinical Drug Testing

Soft-tissue sarcomas (STS) represent a heterogeneous group of rare, malignant tumors of mesenchymal origin. Reliable in vivo sarcoma research models are scarce. We aimed to establish and characterize histologically and molecularly stable patient-derived xenograft (PDX) models from a broad variety of STS subtypes. A total of 188 fresh tumor samples from consenting patients with localized or advanced STS were transplanted subcutaneously in NMRI-nu/nu-immunodeficient mice. Once tumor growth was observed, the material was passaged to a next generation of mice. A patient-derived tumor sample was considered "successfully engrafted" whenever the sample was transplanted to passage 1. A PDX model was considered "established" when observing stable morphologic and molecular features for at least two passages. With every passage, histologic and molecular analyses were performed. Specific genomic alterations and copy-number profile were assessed by FISH and low coverage whole-genome sequencing. The tumor engraftment rate was 32% (61/188) and 188 patient samples generated a total of 32 PDX models, including seven models of myxofibrosarcoma, five dedifferentiated liposarcoma, five leiomyosarcoma, three undifferentiated pleomorphic sarcoma, two malignant peripheral nerve sheet tumor models, and single models of synovial sarcoma and some other (ultra)rare subtypes. Seventeen additional models are in early stages of engraftment (passage 1-2). Histopathologic and molecular features were compared with the original donor tumor and were stable throughout passaging. The platform is used for studies on sarcoma biology and suited for in vivo preclinical drug testing as illustrated by a number of completed and ongoing laboratory studies.

Successful Perioperative and Surgical Treatment of a Rare Case of Extra-Gastrointestinal Stromal Tumor Arising in the Prostate Gland

We report a very uncommon case of a primary, non-metastatic gastrointestinal stromal tumor (GIST) arising in the prostate gland in a 60-year-old patient. The morphology and immunohistochemical profile of the disease resembled GIST of gastrointestinal origin, and the molecular driver of this malignancy was a double mutation in exons 11 and 13 of the KIT gene. The tumor was proliferating slowly, did respond to neoadjuvant therapy with the KIT-inhibiting agent imatinib and was cured by radical, retro-pubic prostatectomy followed by adjuvant imatinib treatment. We postulate that primary GIST tumors of the prostate can arise from prostatic interstitial cells, which are the pacemakers of smooth muscle contractility in the gland, and possibly share a common precursor with typical GIST and the interstitial cells of Cajal in the gastrointestinal tract.

The characteristics of 76 atypical neurofibromas as precursors to neurofibromatosis 1 associated malignant peripheral nerve sheath tumors

Background

Neurofibromatosis 1 (NF1) leads to the development of benign and malignant peripheral nerve sheath tumors (MPNST). MPNST have been described to develop in preexisting benign plexiform neurofibromas (PN) and have a poor prognosis. Atypical neurofibromas (ANF) were recently described as precursor lesions for MPNST, making early detection and management of ANF a possible strategy to prevent MPNST. We aimed to clinically characterize ANF and identify management approaches.

Methods

We analyzed clinical, imaging, and pathology findings of all patients with NF1 and ANF at 3 institutions.

Results

Sixty-three patients had 76 ANF (32M/31F; median age 27.1 y). On MRI, most ANF appeared as distinct nodular lesions and were 18F-fluorodeoxyglucose (FDG) avid. Forty-six ANF were associated with pain, 19 with motor weakness, 45 were palpable or visible, and 13 had no clinical signs. Completely resected ANF (N = 57) have not recurred (median follow-up, 4.1 y; range, 0-14 y). Four ANF transformed into MPNST and 17 patients had a history of MPNST in a different location than was their ANF.

Conclusions

Growth of distinct nodular lesions, pain, and FDG-PET avidity should raise concern for ANF in NF1. Patients with ANF are at greater risk for development of MPNST. Complete resection of ANF may prevent development of MPNST.