Fibrosarcomatous Transformation Research Articles

Exploring the Uncommon: A Series on Dermatofibrosarcoma Protuberans with Rare Locations, Unusual Sites of Metastasis, and Their Close Mimics

Abstract Dermatofibrosarcoma protuberans (DFSP) is an uncommon, slowly growing soft-tissue tumor that involves the dermis, subcutaneous fat and very rarely involves, muscle and deep fascia. It is locally aggressive and an intermediate-grade fibroblastic neoplasm that rarely metastasizes. It is important to know about this entity as it is locally aggressive and has a higher rate of transformation into fibrosarcoma which has an aggressive growth pattern and frequently metastasizes. Apart from this, there are diagnostic challenges, especially in small biopsies, where they resemble other spindle cell neoplasms. This article reviews the clinical and histological features of DFSP as well as possible pitfalls in their diagnosis and how to resolve them. Diagnosed cases of DFSP were retrieved from pathology archives. Their locations and histopathological features along with Immunohistochemistry (IHC) features were reviewed. Our study identified 26 cases of DFSP for 5 years from January 2019 to January 2024 in a tertiary care hospital. The age of study subjects was in the range of 11–70 years. Male:female ratio was 1.30:1. The most common site was shoulder (n = 5). Immunohistochemistry (HC) was performed in cases with diagnostic dilemmas and cases of high-grade transformation. The aim of this study was to perform a retrospective analysis of histopathological features of DFSP to distinguish it from other mimics and emphasize its local aggressiveness, reoccurrence, and rare site of metastasis, especially in cases with fibrosarcomatous transformation. The careful histomorphological examination particularly in smaller biopsies can be challenging, especially in peripheral laboratories and in resource-limited settings.

Recurrent Dermatofibrosarcoma Protuberans with Fibrosarcomatous Transformation: A Case Report

Background: Dermatofibrosarcoma protuberans (DFSP) is a rare cutaneous sarcoma with a propensity for local recurrence but a low risk of distant metastasis. Fibrosarcomatous transformation (FS-DFSP) is a rare but aggressive variant associated with increased metastatic potential. Case presentation: We present the case of a 39-year-old male with recurrent DFSP involving the scalp, mandible, and humerus, complicated by fibrosarcomatous transformation and distant metastases to the lungs and bones. The patient underwent multiple excisions, radiation therapy, and systemic treatments including chemotherapy and imatinib, but ultimately experienced disease progression. Conclusion: This case highlights the challenges in managing recurrent DFSP with fibrosarcomatous transformation. The rarity of this entity necessitates a high index of suspicion for early diagnosis and aggressive multidisciplinary management to improve patient outcomes. Further research is needed to identify effective treatment strategies for this aggressive variant of DFSP.

Dermatofibrosarcoma Protuberans: An Updated Review of the Literature.

Dermatofibrosarcoma protuberans (DFSP) is a rare proliferative condition representing skin sarcomas which is known to locally recur yet very rarely metastasizes. Its genetic background is a reciprocal translocation t(17;22)(q22;q13) that produces COL1A1-PDGFB gene fusion. Complete resection is the primary treatment. The aim of this review is to outline the pathogenesis, diagnosis, and management of DFSP. A clear-cut distinction between low-to-moderate-grade DFSP with excellent prognosis and high-grade fibrosarcomatous DFSP with a much worse prognosis is underlined. Malignant transformation within DFSP (or high histologic grade), older age, being female, large primary tumor size (≥10 cm), narrow surgical margins of excision (<3 cm), surgical margin positivity for tumor cells, short time to recurrence, numerous recurrences, tumor that was recently rapidly enlarging, and presence of pain in the tumor have all been proposed as clinicopathological risk factors for recurrence and metastasis. A tendency for local growth and local relapses of well- and moderately differentiated DFSPs is an argument for their surgical excision, possibly combined with reconstructive surgery, even in patients of advanced age. Another main point of this review is that cases of DFSP with fibrosarcomatous transformation are a challenge and require careful medical attention. Both anatomopathological evaluation of the presence of lymphovascular space invasion and sentinel lymph node biopsy at DFSP surgery merit further study.

Fibrosarcomatous Transformation in Dermatofibrosarcoma Protuberans of the Male Breast and its Association with Magnetic Resonance Imaging and Immunohistopathologic Features.

Dermatofibrosarcoma Protuberans (DFSP) is a rare soft tissue sarcoma, accounting for approximately 1% of all tumors; however, DFSP of the breast is extremely rare. Moreover, DFSP generally has a low malignant potential and is characterized by a high rate of local recurrence along with a small but definite risk of metastasis. The risk of metastasis is higher in fibrosarcomatous transformation in DFSP than in ordinary DFSP. We have, herein, reported a case of a 61-year-old male patient with fibrosarcomatous transformation in DFSP. Preoperative Dynamic Contrastenhanced Magnetic Resonance Imaging (DCE-MRI) of the breast revealed an oval-shaped mass with heterogeneous internal enhancement, a large vessel embedded within, and a washout curve pattern on kinetic curve analysis. The mass exhibited a hyperintense signal on Diffusion-weighted Imaging (DWI), with a low apparent diffusion coefficient value. Histologically, the bland spindle tumor cells were arranged in a storiform pattern. Areas with the highest histological grade demonstrated increased cellularity, cytological atypia, and mitotic activity. Immunohistochemically, Ki-67 and p53 were highly expressed. Recognizing the risk and accurately diagnosing fibrosarcomatous transformation in male breast DFSP are critical for improving prognosis and establishing appropriate treatment and follow-up plans. This emphasizes the significance of combining immunohistopathological features with DCE-MRI and DWI to assist clinicians in the early and accurate diagnosis of sarcomas arising from male breast DFSP.

Current patterns of care and outcomes for dermatofibrosarcoma protuberans: An international multi-institutional collaborative.

Dermatofibrosarcoma protuberans (DFSP) is a cutaneous sarcoma with an infiltrative growth pattern that makes it challenging to clear margins. High quality data regarding DFSP natural history, management, and outcomes are limited. Data were retrospectively collected for adult DFSP patients who underwent resection at 10 institutions in eight countries. Demographics, tumor characteristics, treatment strategies, and outcomes were analyzed. Analysis included 347 patients consisting of young (median, 42 years), White (76.2%), males (54.2%) with truncal lesions (57.3%). The majority (76.8%) were symptomatic at presentation. Preoperative imaging was used in 55.9% of cases. Diagnosis was established with excisional biopsy in 50.9% versus incisional biopsy in 25.0% of cases. Despite planned margins of >1.0 cm in 67.4% of cases, only 69.0% of patients achieved R0 resection. Twenty-two percent of patients underwent at least one re-excision. R0 resection was achieved at a second procedure in 80.2% and a third procedure in 86.2%. Ultimately, R0 resection was feasible in 89.5% of all patients. Fibrosarcomatous transformation (FST) was observed in 12.6%. In total, 6.6% (N=23) recurred (17 local, six distant). Of the six distant recurrences, 50.0% had FST. With a median follow-up of 47.0 months, disease-specific survival rate was 98.8%. In multivariable analysis, R0 margins at index resection were associated with wider circumferential margins and non-FST histology. In this international, multicenter collaborative, DFSP practice patterns were heterogeneous but achieved favorable recurrence rates and survival. Multiple excisions to clear margins remain commonplace and can inform future efforts to optimize margin selection.

A challenging fibrosarcomatous variant of dermatofibrosarcoma protuberans of head and neck: a case report

Dermatofibrosarcoma protuberans (DFSP) is an unusual tumour of soft tissue with local invasive property with high rate of recurrence after surgical treatment. DFSP is frequently seen on the trunk and proximal extremities, although a 10-15% cases accounts in head and neck region. Mainstay for success of surgery in DFSP remains complete removal of tumour with adequate surgical margins of approximately 3cms. In head neck region challenges associated with surgery may be inadequate surgical margins, poor functional and cosmetic outcomes. We present a case of a 35 years old male reported to our hospital with complaint of rapidly growing mass over right cheek and retroauricular region causing facial deformity. Incisional biopsy diagnosis was made DFSP. The patient underwent wide local excision of tumour followed by adjuvant radiotherapy. Final histopatholgy showed fibrosarcomatous transformation of DFSP. After 24 months of post-op follow up, patient recovery was satisfactory without any signs of recurrence. This case is presented for its rarity and it highlights the need for proper diagnosis and treatment plan.

Multi-omic profiling and real time ex vivo modelling of imatinib-resistant dermatofibrosarcoma protuberans with fibrosarcomatous transformation.

Dermatofibrosarcoma protuberans (DFSP) is a rare and indolent cutaneous sarcoma, with the risk of aggressive fibro-sarcomatous transformation. Limited effective options are available for un-resectable or metastatic DFSP beyond targeting the oncogenic PDGF pathway with imatinib therapy. We established a patient-derived xenograft (PDX) and cell line model (designated MDFSP-S1) of imatinib-resistant DFSP with fibro-sarcomatous transformation. Whole genome sequencing identified high-level amplification at chromosomes 17 and 22, whilst homozygous deep deletion was demonstrated at chromosome 9 (CDKN2A, CDKN2B, MTAP). RNA sequencing followed by Sanger sequencing confirmed the pathognomonic COL1A1-PDGFB t (17;22) rearrangement in the original tumour, PDX and cell line model. Immunohistochemistry profiles of the PDX model were consistent with the patient's tumour sample (CD34 + /MIB1 + /SOX10- ). Gene set enrichment analysis highlighted top-scoring Hallmark gene sets in several oncogenic signalling pathways, including potentially targetable MTORC1 signalling and angiogenesis pathways. Antiangiogenic agents (sunitinib, regorafenib, pazopanib, axitinib) and the third-generation irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor osimertinib exhibited modest anti-proliferative activity in the cell line, with IC50 values between 1 and 10µM at 72h. No significant activity was observed with imatinib, palbociclib, everolimus, olaparib, gefitinib and erlotinib (IC50 all > 10µM). In conclusion, we established MDFSP-S1, a new PDX and cell line model of imatinib-resistant DFSP with fibro-sarcomatous transformation.

Establishment and characterization of NCC-DFSP4-C1: a novel cell line from a patient with dermatofibrosarcoma protuberans having the fibrosarcomatous transformation.

Dermatofibrosarcoma protuberans (DFSP) is a superficial low-grade sarcoma, genetically characterized by a fusion gene in collagen type I α (COL1A1) gene and platelet-derived growth factor subunit β (PDGFB). DFSP is locally aggressive and does not typically metastasize. However, DFSP with fibrosarcomatous transformation, which occurs in 7-16% of DFSP cases, demonstrates a poor prognosis than classic DFSP with a higher local recurrence rate and metastatic potential. Although imatinib, a PDGF receptor inhibitor, is a potent therapeutic agent for classic DFSP, it is less effective for DFSP with fibrosarcomatous transformation. The development of definitive chemotherapies for DFSP with fibrosarcomatous transformation is required. Patient-derived tumor cell lines are indispensable tools for preclinical research to discover novel therapeutic agents. However, only seven cell lines were derived from DFSP, out of which only two were established from DFSP with fibrosarcomatous transformation. Hence, in the present study, we established a novel DFSP cell line, NCC-DFSP4-C1, from a surgically resected DFSP tumor specimen with fibrosarcomatous transformation. NCC-DFSP4-C1 harbored an identical COL1A1-PDGFB fusion gene as its donor tumor. NCC-DFSP4-C1 cells retained the morphology of their donor tumor and demonstrated constant proliferation, spheroid formation, and invasion capability in vitro. By screening a drug library, we found that bortezomib and romidepsin demonstrated the strongest suppressive effects on the proliferation of NCC-DFSP4-C1 cells. In conclusion, we report a novel cell line of DFSP with fibrosarcomatous transformation, and demonstrate its utility in the development of novel therapeutic agents for DFSP.

Possible role of the collagen type I alpha 1–platelet‐derived growth factor beta chain fusion gene in the development of dermatofibrosarcoma protuberans with fibrosarcomatous transformation

AbstractDermatofibrosarcoma protuberans with fibrosarcomatous transformation (DFSP‐FS) is a rare variant, with higher rates of recurrence and metastasis than DFSP. Detection of the collagen type I alpha 1 (COL1A1)–platelet‐derived growth factor beta chain (PDGFB) fusion gene is useful for the diagnosis of DFSP. In this letter, we report a case of DFSP‐FS, focusing on the expression of the COL1A1‐PDGFB fusion gene in the lesions. Increased expression of the COL1A1‐PDGFB fusion gene may be associated with fibrosarcomatous changes during the pathogenesis of DFSP.

Comprehensive analysis of transcriptome characteristics and identification of TLK2 as a potential biomarker in dermatofibrosarcoma protuberans.

Background: Dermatofibrosarcoma protuberans (DFSP) is a rare cutaneous sarcoma characterized by local invasion and recurrence. RNA sequencing (RNA-seq) allows the qualification of cellular RNA populations and provides information on the transcriptional state. However, few studies have comprehensively analyzed DFSP transcriptional data. Methods: Fourteen DFSP samples with paired non-neoplastic soft tissue from Chinese patients undergoing Mohs micrographic surgery were used for RNA-seq analysis. Differential expression analysis and enrichment analysis for RNA-seq data were performed to identify fusion genes, biomarkers, and microenvironment characteristics of DFSP. Results: This study systemically describes the transcriptomic characteristics of DFSP. First, we performed gene fusion analysis and identified a novel FBN1-CSAD fusion event in a DFSP patient with fibrosarcomatous transformation. Then, we identified TLK2 as a biomarker for DFSP based on functional enrichment analysis, and validated its accuracy for diagnosing DFSP by immunohistochemical staining and joint analysis with public data. Finally, microenvironment analysis described the infiltration characteristics of immune and stromal cells in DFSP. Conclusion: This study demonstrates that RNA-seq can serve as a promising strategy for exploring molecular mechanisms in DFSP. Our results provide new insights into accurate diagnosis and therapeutic targets of DFSP.

Molecular Characterization of Dermatofibrosarcoma Protuberans: The Clinicopathologic Significance of Uncommon Fusion Gene Rearrangements and Their Diagnostic Importance in the Exclusively Subcutaneous and Circumscribed Lesions.

The clinicopathologic relevance of various gene rearrangements underlying dermatofibrosarcoma protuberans (DFSP) remains insufficiently characterized. In 188 DFSPs, we determined PDGFB, COL1A1, PDGFD, COL6A3, and EMILIN2 rearrangements by fluorescence in situ hybridization (FISH). The clinicopathologic significance of rearrangement types and factors related to recurrence and metastasis were statistically analyzed. In all, classic PDGFB rearrangement, cryptic COL1A1-PDGFB fusion, and PDGFD rearrangement were identified in 172 (91.4%), 8 (4.3%), and 8 (4.3%: 4 COL6A3-PDFGD, 4 EMILIN2-PDGFD) cases, respectively. In an index DFSP harboring the cryptic fusion, the COL1A1-PDGFB transcript was confirmed by both RNA sequencing and reverse transcription-polymerase chain reaction. In comparison with cases harboring classic PDGFB rearrangement, cryptic PDGFB-rearranged DFSPs usually exhibited higher 5'-COL1A1 copy numbers. In a combined reappraisal of published and current cases, COL6A3-PDGFD-positive DFSPs (n=16) predominated in females (n=14, 88%) and torso (n=14, 88%), especially the breast (n=7, 44%); EMILIN2-PDGFD-positive DFSPs (n=6) preferentially demonstrated near exclusively subcutaneous growth (n=5, 83%) and fibrosarcomatous transformation (n=5, 83%). In our cohort, local recurrence was related to fibrosarcomatous variant (P=0.029, odds ratio=3.478) and head and neck location (P=0.046, odds ratio=3.508). Distant metastasis only occurred in the fibrosarcomatous variant (9/73, 12.3%) but not in other cases. In conclusion, 8.6% of DFSPs are negative for PDGFB break-apart FISH, which, especially those with challenging subcutaneous and circumscribed manifestation, require complementary diagnosis by FISH assays targeting COL1A1 and PDGFD. The types of fusion gene rearrangements, head and neck location, and fibrosarcomatous transformation may account for clinicopathologic and prognostic variations in DFSPs and warrant future independent validation.

Rare giant dermatofibrosarcoma protuberans with uncommon fibrosarcomatous transformation - case report and review of literature

Dermatofibrosarcoma protuberans (DFSP) is a rare soft tissue sarcoma with aggressive local behavior but with a low metastatic potential. Although slow growing and indolent, they rarely reach huge sizes. Very uncommonly, these locally invasive tumors undergo fibrosarcomatous transformation with a more aggressive clinical course, with higher rate of recurrence risk and distant metastases. A 32-years-old lady, presented with a gradually progressive lump in the upper central back for the past 6 years, with rapid progression in size during the last 6 months. On examination, she had a single lump of size 18×18 cm in the midline of the upper back, with prominent veins over its surface. Magnetic resonance imaging (MRI) showed no connection with the spinal canal and appeared flush with the paraspinal muscles. Core needle biopsy showed DFSP. The patient underwent a wide local excision with split skin grafting. The histopathology now showed a fibrosarcomatous transformation of DFSP. The patient again underwent a wide re-excision with a 3 cm margin. Histology reported no evidence of tumor cells in the specimen. The patient’s postoperative period was uneventful and she was referred for adjuvant radiotherapy. DFSP is a rare, slow-growing malignant fibroblastic mesenchymal skin tumor with low metastatic potential. However, in any patient with long standing DFSP with a recent increase in size, this fibrosarcomatous transformation must be kept in mind as it represents an uncommon form of DFSP that tends to follow a more aggressive clinical course, with higher rate of recurrence risk and distant metastases.

Rare Lower Extremity Fibrosarcomatous Variant of Dermatofibrosarcoma With Myxoid Features Treated With Transtibial Amputation

Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft tissue tumor originating from the dermis, with high rates of local recurrence and invasive growth but low likelihood of distant metastasis. Fibrosarcomatous transformation (FS-DFSP) of DFSP accounts for approximately 5-15% of DFSP tumors, is a higher-grade tumor, with higher chances of metastasis and poorer prognosis. We present a case of a 66-year-old female presented with a large fungating mass on the left dorsal foot. Ultrasound-guided core needle biopsy with immunohistochemistry suggested a spindle cell neoplasm, favoring myxofibrosarcoma with intermediate grade. The patient elected for below-knee amputation over limb salvage with wide resection and free flap reconstruction. Based on clinical presentation, radiologic, histologic features and fluorescence in situ hybridization (FISH) studies confirmed the diagnosis of fibrosarcomatous variant of dermatofibrosarcoma protuberans with myxoid change. FS-DFSP with myxoid change is a rare soft tissue tumor that requires aggressive treatment due to its high rates of recurrence. This case presents a rare tumor in a unique location that was successfully treated with limb amputation, which is not documented in current literature.

Novel TNC-PDGFD fusion in fibrosarcomatous dermatofibrosarcoma protuberans: a case report

BackgroundDermatofibrosarcoma protuberans (DFSP) is a superficial fibroblastic tumor characterized by high rate of local recurrence and low metastatic potential. Fibrosarcomatous transformation can rarely arise in DFSP either de novo or as recurrent, which represents a form of tumor progression and carries an increased risk of metastasis over classic DFSP. Cytogenetically, DFSP is characterized by a recurrent unbalanced chromosome translocation t (17;22)(q22;q13), leading to the formation of COL1A1-PDGFB fusion transcript that is present in more than 90% of cases. Alternative fusions involving the PDGFD with partners of COL6A3 or EMILIN2 have recently been documented in less than 2% of cases. Herein, we report a DFSP with fibrosarcomtous morphology harboring a novel TNC-PDGFD fusion.Case presentationA 54-year-old female presented with a slowly growing mass in the right thigh. Excision demonstrated a 2-cm ovoid, well-circumscribed, gray-white, mass. Microscopic examination revealed a partially encapsulated subcutaneous nodule without dermal connection. The neoplasm was composed of cellular and fairly uniform spindle cells with brisk mitoses, arranged in elongated fascicles and herringbone patterns, with focal collagenized stroma. The neoplastic cells were positive for CD34 and smooth muscle actin. Fluorescence in-situ hybridization analyses showed negative for COL1A1-PDGFB fusion as well as NTRK1/2/3 rearrangements. A subsequent RNA sequencing detected an in-frame fusion between exon 15 of TNC and exon 6 of PDGFD. This fusion was further confirmed by nested reverse transcription polymerase chain reaction amplification followed by Sanger sequencing. A diagnosis of fibrosarcomatous DFSP was rendered and the patient was in good status at a follow-up of 12 months after the operation.ConclusionsWe report a fibrosarcomatous DFSP with novel TNC-PDGFD fusion, which adds to the pathologic and genetic spectrum of PDGFD-rearranged DFSP.

When an old pigmented lesion becomes serious: the problematic diagnosis of low-grade skin malignancies – Bednar tumor with fibrosarcomatous transformation

Abstract Bednar tumor is a rare cutaneous neoplasm, regarded as a variant of dermatofibrosarcoma protuberans with melanotic colonization and it usually affects young and middle-aged adults or children. This lesion is considered a low-grade malignant tumor, which can be associated with multiple local recurrences after surgical excision. Although a rare phenomenon, these lesions may undergo fibrosarcomatous transformation, which implies a poorer prognosis of the disease, as the tumor has a more locally aggressive behavior and patients might also develop distant metastases. We present the case of a 53-year-old female patient, with no significant medical history, who presented with a subcutaneous nodule on her upper back, for which a wide surgical excision was performed. The gross examination of the specimen showed a solitary protuberant grey-white nodule with a bluish shade and flecked with pigment. The microscopic examination revealed a malignant proliferation with a predominantly fascicular growth pattern, composed of spindle cells with highly pleomorphic nuclei and high mitotic rate, as well as the presence of dendritic cells with abundant melanin. Upon immunohistochemical analysis, the proliferation showed negative staining for CD 34 and AE 1/3, whereas the scattered dendritic cells stained positive with S100 protein. Ki 67 was positive in 15% of the tumor cells and the absence of p53 expression was noted. Thus, the diagnosis of Bednar tumor with fibrosarcomatous transformation was established. The aim of this paper was to gain further knowledge about the histopathological and immunohistochemical features, as well as about the treatment of Bednar tumor, especially considering its rarity.

Long-Term Outcome of Neoadjuvant Tyrosine Kinase Inhibitors Followed by Complete Surgery in Locally Advanced Dermatofibrosarcoma Protuberans.

Simple SummaryWide surgical excision is the standard treatment for dermatofibrosarcoma protuberans. Imatinib mesylate has been reported as an efficient neoadjuvant therapy to surgery in order to reduce tumor size and post-operative relapses for locally advanced or unresectable tumors. The aim of this study was to evaluate the long-term status of patients with advanced dermatofibrosarcoma protuberans treated by neoadjuvant tyrosine kinase inhibitors. Based on the data of 27 patients in our center, locally advanced and unresectable DFSP were efficiently treated with neoadjuvant tyrosine kinase inhibitors followed by complete surgery with micrographic analysis with durable local recurrence disease-free survival and few severe adverse events.In locally advanced dermatofibrosarcoma protuberans (DFSP), imatinib mesylate has been described as an efficient neoadjuvant therapy. This retrospective study included patients with locally advanced DFSP who received neoadjuvant TKI (imatinib or pazopanib) from 2007 to 2017 at Saint Louis Hospital, Paris. The primary endpoint was the evaluation of the long-term status. A total of 27 patients were included, of whom nine had fibrosarcomatous transformation. The median duration of treatment was 7 months. The best response to TKI treatment before surgery, evaluated according to RECIST1.1 on MRI, consisted of complete/partial response (38.5%) or stability (46.2%). DFSP was surgically removed in 24 (89%) patients. A total of 23 patients (85%) were disease-free after 64.8 months of median follow-up (95% confidence interval 47.8; 109.3). One patient developed distant metastases 37 months after surgical tumor resection and finally died. Two patients (7%) did not get surgery because of metastatic progression during TKI treatment, and one patient refused surgery even though the tumor decreased by 30%. Treatment-related adverse events (AE) occurred in 23 patients (85%). Only four patients (imatinib: n = 3, pazopanib: n = 1) had grade ≥3 AE requiring temporary treatment disruption. Neoadjuvant TKI followed by complete surgery with micrographic analysis is an effective strategy for locally advanced and unresectable DFSP, with durable local recurrence disease-free survival.

PDGFB RNA in situ hybridization for the diagnosis of dermatofibrosarcoma protuberans.

Dermatofibrosarcoma protuberans (DFSP) is a spindle cell neoplasm of the skin and superficial soft tissue with a tendency for locally aggressive behavior; metastatic potential coincides with fibrosarcomatous transformation. The vast majority of DFSPs harbor the t(17;22) translocation resulting in a COL1A1-PDGFB fusion that drives autocrine growth stimulation via PDGFB overexpression. Here, we examined the utility of PDGFB RNA chromogenic in situ hybridization (CISH) for the diagnosis of DFSP. A total of 337 tumors represented in whole tissue sections and tissue microarrays, including 37 cases of DFSP and 300 histologically similar spindle cell tumors, were subjected to PDGFB RNA CISH using commercially available probes. PDGFB overexpression was observed by light microscopy in 24 of 26 conventional DFSPs (92%) and 11 of 11 fibrosarcomatous DFSPs (100%). One of two DFSPs negative for PDGFB by RNA CISH was found to harbor an uncommon alternative rearrangement involving PDGFD. All examined cases of histologic mimics were negative for PDGFB overexpression; limited PDGFB expression, not reaching an empirical threshold of greater than 5 puncta or one aggregate of chromogen in more than 25% of cells, was observed in 7 of 300 mimics (2.3%), including desmoplastic melanoma, malignant peripheral nerve sheath tumor, angiosarcoma, and pleomorphic dermal sarcoma. Vascular PDGFB expression was seen in several tumor types. We conclude that PDGFB RNA CISH, with careful interpretation and the use of appropriate thresholds, may serve as a surrogate marker of PDGFB rearrangement and a useful ancillary tool for the diagnosis of DFSP.

Dermatofibrosarcoma protuberans: the diagnosis of high-grade fibrosarcomatous transformation.

Dermatofibrosarcoma protuberans (DFSP) is an intermediate-grade tumour which may undergo fibrosarcomatous transformation to a high-grade sarcoma (DFSP-FST). DFSP-FST requires wide local resection, and therefore, pre-operative identification is important. The aims of this study are to see if DFSP and DFSP-FST can be differentiated based on MRI appearances, and to determine the ability of ultrasound-guided core needle biopsy (US-CNB) to identify DFSP-FST. Retrospective review of patients with a histological diagnosis of DFSP with/without transformation to DFSP-FST. Patient age, gender, lesion location and maximal size were recorded, as were several MRI features. MRI studies were reviewed independently by 2 musculoskeletal radiologists and the assessed features were then compared with final surgical resection histology. Histological results of US-CNB were also compared with final surgical pathology. A total of 42 patients were included, 26 males and 16 females with a mean age of 41.3years (range 3-78years). The upper limb was involved in 12 cases, the lower limb in 17 and the trunk in 13. Final surgical histological diagnosis was DFSP in 21 (50%) cases and DFSP-FST in 21 (50%) cases. Mean tumour dimension for DFSP was 32mm and DFSP-FST 68mm (p < 0.001). MRI features indicative of DFSP-FST included multi-lobular morphology (p = 0.03), T2W hypointensity compared with fat (p = 0.03), internal flow voids (p = 0.03) and peri-tumoral oedema (p < 0.001). Only 3 cases of DFSP-FST were correctly diagnosed on US-CNB. Various MRI findings can suggest a diagnosis of DFSP-FST, but US-CNB is unreliable at identifying high-grade fibrosarcomatous transformation.

1703P - Long-term outcome of neoadjuvant tyrosine kinase inhibitors (TKI) in locally advanced dermatofibrosarcoma protuberans (DFSP)

BackgroundImatinib mesylate is approved in unresectable tumors and has been also proposed in the neoadjuvant setting in order to reduce tumor size and post-operative relapses for difficult to resect DFSP. The aim of this study was to evaluate the long-term results of neoadjuvant imatinib and other TKI used in DFSP. MethodsThe files of all patients with the following criteria seen from 2007 to 2017 in our center were collected in this retrospective study: a/histologically proven primary or recurrent DFSP with COL1A1-PDGFB translocation b/ difficult to treat but surgically manageable as assessed in pluridisciplinary tumor board, c/received first-line neoadjuvant TKI (imatinib, pazopanib). The primary endpoint was long-term progression-free survival (PFS). Results27 patients (median 42 years, range: 18-63) were included, of whom 9 (33%) had fibrosarcomatous transformation on pre-TKI biopsy. 10 patients had primary tumors and 17 presented recurrences. Median tumor size was 6cm (range 3-30). 24 patients received imatinib (median dose= 600mg/day), 3 received pazopanib (median dose= 600mg/day) for a median of 7 months. The best MRI response to ITK treatment before surgery according to RECIST1.1 consisted of complete/partial response (33%) or stability (48%). DFSP was surgically removed in 24 patients (89%) after a median of 7 months and 2 surgeries. Two patients (7%) did not receive surgery because of metastasis progression. One other patient declined surgery. 23 of 24 patients surgically treated were disease-free after 50 months of median follow-up (range 10-133). One patient developed distant metastasis 37 months after the complete surgical resection. The median PFS was 44 months (range 10-133).The histological response localization was mainly patchy (n=10) or diffuse (n=7). The median percentage of therapeutic response surface was 65%.Treatment-related adverse events occurred in 23 patients (85%). 4 patients had grade 3 or higher toxicities (2 grade 3 and 4 neutropenia, 1 grade 3 cholestasis, 1 grade 3 nausea) requiring temporary treatment disruption and dose reductions. ConclusionsTKI are effective neoadjuvant treatment for locally advanced or inoperable DFSP with long-term PFS and few severe adverse events. Legal entity responsible for the studyThe authors. FundingHas not received any funding. DisclosureAll authors have declared no conflicts of interest.

Systemic therapy in advanced dermatofibrosarcoma protuberans: Imatinib and beyond.

e22523 Background: Imatinib is the standard treatment of advanced Dermatofibrosarcoma (DFSP). However ideal treatment of advanced DFSP patients, who have progressive disease (PD) on imatinib, remains an unanswered question. Methods: We retrospectively analysed consecutive advanced DFSP patients who presented to AIIMS Sarcoma Medical Oncology clinic between January 2016 and January 2019. Results: There were eleven patients, with median age of 35 years, seven (63.6%) of which were males. Fibrosarcomatous transformation was present in six (54.5%) patients. Four (36.4%) had locally advanced disease, while seven (63.6%) had metastatic disease. Primary site was trunk in eight (63.7%) patients. Three (75%) of the four patients who received neoadjuvant imatinib, underwent complete surgical resection. Initial dose of imatinib was 400mg OD in eight (72.7%) patients, 600 mg OD in two (18.2%) and 800 mg OD in one (9.1%) patient. The best response to imatinib was Partial response (PR) in nine (81.8%) patients, stable disease (SD) in one (9.1%) and primary PD in one (9.1%) patient. Median progression free survival (PFS) was 16 months, after a median follow up of 14 months. Five (45.4%) patients had PD on imatinib. As mentioned in table, strategies used in these patients were pazopanib (n = 3), doxorubicin (n = 2), other chemotherapy (n = 2), dose escalation of imatinib (n = 2) and reintroduction of imatinib (n = 1). One patient had prolonged stable disease on pazopanib, while remaining had PD. Conclusions: Imatinib remains prominent first line therapy in advancved DFSP. Though pazopanib has shown some promise, the treatment outcomes in second line therapy and beyond have largely been dismal and need to be studied prospectively.[Table: see text]