30A ANNUAL MEETING ABSTRACTS Conclusions: Our data further demonstrate the complex genetics associated with Results: Patterns identified included: conventional (165 cases, range 10-100%), leiomyosarcomas. As a class, tumor suppressor genes were the most commonly hypocellular/hyalinized (46 cases, range 5-80%), staghorn vessels (35 cases, range mutated loci, including TP53, mutated in 36% of cases (9/25). The loss of key tumor 5-30%), myxoid (27 cases, range 5-40%), keloid (24 cases, range 5-50%), nodular suppressor genes is consistent with our observations that CNV was present in 85% of fasciitis-like (15 cases, range 5-40%), and hypercellular (6 cases, range 5-20%). Tumors leiomyosarcomas. While no common therapeutically targetable gene was identified with keloid areas, as well as those with prominent staghorn blood vessels, mimicked across these cases, future large cohort sequencing studies of leiomyosarcomas may entities such as solitary fibrous tumor. Those cases with nodular fasciitis-like areas raised provide a means for the molecular classification of these tumors and identify new the possibility of nodular fasciitis and reactive processes. Hypercellular foci led to the treatment paradigms. consideration of spindle cell sarcoma, while the differential diagnosis of hypocellular/ hyalinized areas was broad. By site, the greatest variation of patterns was observed in 107 Identification of a Novel FN1-FGFR1 Genetic Fusion as a Frequent intra-abdominal lesions, and men showed more morphologic variability than females. Event in Phosphaturic Mesenchymal Tumor Adults (>18 years) exhibited more histologic diversity than adolescent and pediatric patients (< 18 years). Chang-Tsu Yuan, Yung-Ming Jeng, Sheng-Yao Su, Cher-Wei Liang, Chung-Yen Lin, Conclusions: The morphologic spectrum of desmoid-type fibromatosis is diverse and Shu-Hwa Chen, Cheng-Han Lee, Jodi Carter, Chen-Tu Wu, Andrew Folpe, Jen-Chieh often underappreciated. Intra-abdominal lesions tend to show the greatest morphologic Lee. National Taiwan University Hospital and National Taiwan University College diversity, and awareness of the histologic patterns that may occur is necessary to prevent of Medicine, Taipei, Taiwan; Academia Sinica, Taipei, Taiwan; University of Alberta misdiagnosis, especially on small biopsy specimens. and Royal Alexandra Hospital, Edmonton, AB, Canada; Mayo Clinic, Rochester, MN. Background: Phosphaturic mesenchymal tumors (PMT) are unusual soft tissue and bone tumors that typically cause hypophosphatemia and tumor-induced osteomalacia 110 Myxoinflammatory Fibroblastic Sarcoma (MIFS) and Hybrid through secretion of phosphatonins such as fibroblast growth factor 23 (FGF23). PMT Hemosiderotic Fibrolipomatous Tumor (HFLT)/ MIFS: Related or Not? A has recently been accepted by the World Health Organization as a formal tumor entity. Clinicopathological and Molecular Cytogenetic Study of 34 Cases The genetic basis and oncogenic pathways underlying its tumorigenesis remain obscure. Riyam Zreik, Jodi Carter, William Sukov, William Ahrens, Karen Fritchie, Elizabeth Design: Four PMT samples were subjected to RNA sequencing in search of possible Montgomery, Sharon Weiss, Andrew Folpe. Mayo Clinic, Rochester, MN; Carolinas fusion transcripts, which would be confirmed by genomic DNA PCR, RT-PCR and Medical Center, Charlotte, NC; Johns Hopkins, Baltimore, MD; Emory University, western blotting. Fluorescence in situ hybridization (FISH) was performed on a total Atlanta, GA. of 15 cases to check the presence of the fusion gene. Background: MIFS, a locally aggressive, rarely metastasizing fibroblastic tumor that Results: Three of the four cases were found harboring a novel FN1-FGFR1 fusion typically involves the distal extremities, has been reported to show t(1;10)(TGFBR3- gene by RNA sequencing, which was confirmed by DNA PCR and RT-PCR. Western MGEA5) in some instances. This genetic event has also been reported in HFLT, and in blotting corroborated the presence in two cases of the chimeric FGFR1 protein with rare tumors showing hybrid features of HFLT and MIFS. These findings have led to increased sizes. FISH showed 6 cases with FN1-FGFR1 fusion, out of an additional speculation that HFLT and MIFS are closely related. However, areas resembling HFLT 11 PMTs. Overall, 60% (9/15) harbored this fusion. have been present in only a very small minority (~1%) of previously reported MIFS, Conclusions: We for the first time identified a highly recurrent genetic event in PMTs. and we recently found TGFBR3 or MGEA5 rearrangements in only 1 of 6 studied The FN1-FGFR1 fusion gene likely has an important role in tumorigenesis and may cases. Thus the relationship between MIFS and HFLT is still unclear. We studied the also have potential therapeutic implications. The FN1 gene possibly provides its clinicopathological and molecular cytogenetic features of 34 cases of MIFS and hybrid constitutively active promoter and the encoded protein’s oligomerization domains to HFLT/MIFS with the goal of clarifying these issues. over-express and facilitate the activation of the FGFR1 kinase domain. Interestingly, Design: Available slides from 38 cases diagnosed as “MIFS” or “hybrid HFLT/MIFS” the FN1-FGFR1 chimeric protein, with various fusion points, was predicted to preserve were retrieved from our archives. Following re-review by 2 experienced soft tissue its ligand-binding domains, suggesting an advantage of the presence of its ligands (such pathologists, 4 cases were excluded, leaving a final group of 27 MIFS and 7 hybrid as FGF23) in the activation of the chimeric receptor tyrosine kinase, thus effecting HFLT/MIFS. Cases were tested for TGFBR3 and MGEA5 gene rearrangements using an autocrine or paracrine mechanism of tumorigenesis. Further study is required to previously published methods. confirm these hypotheses. Results: MIFS occurred in 10F and 17M, with a mean age of 45 years (range 15-82 years) and involved the hand/arm (N=12), foot/leg (N=14), and cheek (N=1). Hybrid 108 A Subset of Spindle Cell Lipomas Harbors Rearrangements of the HFLT/MIFS occurred in 6F and 1M, with a mean age of 60 years (range 49-78 years) HMGA1 Locus and involved the foot (N=4) and leg (N=3). All MIFS conformed strictly to the current WHO definition; no case showed areas resembling HFLT. Hybrid HFLT/MIFS showed Riyam Zreik, Xiaoke Wang, Jorge Torres-Mora, Karen Fritchie, Andre Oliveira. Mayo zones of classical HFLT juxtaposed to areas of myxoid sarcoma, showing some but Clinic, Rochester, MN. not all features of classical MIFS. By FISH, 11 informative MIFS were negative for Background: Spindle cell lipomas are benign adipocytic neoplasms composed of TGFBR3 or MGEA5 rearrangements. In contrast, 2 of 4 tested hybrid HFLT/MIFS varying amounts of mature adipose tissue, bland spindle cells, and collagen fibers. A showed TGFBR3 or MGEA5 rearrangement. single case of spindle cell lipoma with t(2;6)(p16~21;p21) expressing HMGA1 protein Conclusions: Our morphological and FISH findings suggest that MIFS and was reported by Dumollard JM et al in 2001. We have encountered a second case with hybrid HFLT/MIFS may be unrelated, with the latter entity representing a form of classic histologic features and t(1;6)(p32;p21.3). This finding led us to hypothesize that, morphological progression within HFLT. We speculate that not all studies may have similar to ordinary lipomas, a subset of spindle cell/pleomorphic lipomas could also utilized the same diagnostic criteria for MIFS. On-going FISH study of the remaining harbor rearrangements of the chromatin remodeling gene HMGA1. cases should help to clarify these issues. Design: Twenty-four spindle cell lipomas and 8 pleomorphic lipomas with classic histologic features were retrieved from our institutional archives and screened for rearrangements of the HMGA1 and HMGA2 loci using custom-designed break apart FISH probes. The spindle cell lipomas were seen in 20 males and 4 females with a mean Breast Pathology age of 59 years (range 40-86 years) and involved most frequently the neck (7), back (7), face/ear (3), arm/shoulder (2), thigh (2), buttock (2), and labia (1). The pleomorphic 111 Multicenre Genomic and Protein Expression Analysis Reveals lipomas were seen in 7 males and 1 female with a mean age of 56 years (range 37-72 SPAG5 as a Key Oncogene and Biomarker and a Target for Personalized years) and involved the shoulder/neck (4), ear/scalp (3) and back (1). Therapy in Breast Cancer (BC) Results: Balanced rearrangements of the HMGA1 locus were found in 3 (of 24; 13%) Tarek Abdel-Fatah, Dongxu Iu, Devika Agarwal, Paul Moseley, Andrew Green, Ian spindle cell lipomas but in no pleomorphic lipoma. All tumors were negative for Ellis, Graham Ball, Steven Chan. Nottingham City Hospital NHS Trust, Nottingham, HMGA2 rearrangements. United Kingdom. Conclusions: Similar to ordinary lipomas, a small subset of spindle cell lipomas harbors Background: Recently our neural network analysis of Breast Cancer gene expression rearrangements of the HMGA1 locus. This finding suggests that these two subtypes of array (GEA) data has revealed SPAG5 as a major hub in the proliferation pathway. lipoma may share common oncogenic pathways, at least in a subset of cases. Further In this study pre-clinical, molecular and clinicopathological functions of SPAG5 was studies are needed to better understand the biologic implication of this novel finding investigated in patient cohorts from multi-centres. in spindle lipoma pathogenesis. Design: 1. The expression and functionality of SPAG5, its relationships