Efficacy and Biological Activity of Imatinib in Metastatic Dermatofibrosarcoma Protuberans (DFSP)

Molecular Alterations in Pediatric Solid Tumors

Pediatric tumors can be divided into hematologic malignancies, central nervous system tumors, and extracranial solid tumors of bone, soft tissue, or other organ systems. Molecular alterations that impact diagnosis, prognosis, treatment, and familial cancer risk have been described in many pediatric solid tumors. In addition to providing a concise summary of clinically relevant molecular alterations in extracranial pediatric solid tumors, this review discusses conventional and next-generation sequencing-based molecular techniques, relevant tumor predisposition syndromes, and the increasing integration of molecular data into the practice of diagnostic pathology for children with solid tumors.

[Side effects of dermato-oncologic therapies]

BACKGROUND

Immune checkpoint inhibitors (ICIs) such as PD(L)1 and CTLA4 antibodies as well as targeted therapies such as BRAF and MEK inhibitors have significantly improved the systemic treatment of skin cancer in adjuvant and advanced therapy settings. All these drugs differ in their spectrum of side effects.

MATERIALS AND METHODS

The aim of this article is to provide an overview of the spectrum of side effects of dermato-oncological therapies and their management, taking into account the current literature.

RESULTS

The most important side effects of ICIs, the CCR4 inhibitor mogamulizumab, the ImmTAC tebentafusp, the BRAF and MEK inhibitors and the multityrosine kinase inhibitor imatinib are considered.

CONCLUSIONS

Side effects can manifest themselves in all organ systems. Chronic side effects and long-term harm are possible, especially with ICIs, and require close therapy monitoring and patient education. Knowledge of the side effects and the temporal, sometimes delayed course of their occurrence are essential for diagnosis and prompt initiation of therapy.

Precision Oncology in Melanoma and Skin Cancer Surgery

There has been perhaps no greater advance in the prognosis of solid tumors in the last decade than for patients with metastatic melanoma. This is due to significant improvements in treatment based on two key components of melanoma tumor biology (1) the identification of driver mutations with therapeutic potential and (2) the mechanistic understanding of a tumor-specific immune response. With breakthrough findings in such a relatively short period of time, the treatment of patients with metastatic melanoma has become intensely personalized.

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 10 µM at 72 h. No significant activity was observed with imatinib, palbociclib, everolimus, olaparib, gefitinib and erlotinib (IC50 all > 10 µM). In conclusion, we established MDFSP-S1, a new PDX and cell line model of imatinib-resistant DFSP with fibro-sarcomatous transformation.

Dermatofibrosarcoma protuberans: a case report of an abdominal wall mass and review of the literature

Dermatofibrosarcoma protuberans (DFSP) is a rare, slow-growing malignancy that often presents with an ambiguous clinical presentation due to its nonspecific findings. We present the case of a 41-year-old male who presented with a slow-growing mass on his abdomen that became protuberant and firm, prompting his desire to pursue excision. Upon return of histologic examination, the specimen was noted to be DFSP. DFSP is a rare cutaneous neoplasm that originates from the dermis and invades the underlying tissue creating a classic protuberant appearance. In some cases, chemotherapy and radiation may be indicated based on margins and locations. The sarcoma is notoriously complicated with early recurrence, making the disease process difficult to control. Surgeons should be familiar with this malignancy due to the indication of additional nonsurgical treatments and the necessity for long-term follow-up for surveillance of recurrence.

Integrated analysis of canine soft tissue sarcomas identifies recurrent mutations in TP53, KMT genes and PDGFB fusions

Soft tissue sarcomas (STS) are a heterogenous group of mesenchymal tumors representing over 50 distinct types with overlapping histological features and non-specific anatomical locations. Currently, localized sarcomas are treated with surgery + / -  radiation in both humans and dogs with few molecularly targeted therapeutic options. However, to improve precision-based cancer therapy through trials in pet dogs with naturally occurring STS tumors, knowledge of genomic profiling and molecular drivers in both species is essential. To this purpose, we sought to characterize the transcriptomic and genomic mutation profiles of canine STS subtypes (fibrosarcoma, undifferentiated pleomorphic sarcoma, and peripheral nerve sheath tumors), by leveraging RNAseq, whole exome sequencing, immunohistochemistry, and drug assays. The most common driver mutations were in cell cycle/DNA repair (31%, TP53-21%) and chromatin organization/binding (41%, KMT2D-21%) genes. Similar to a subset of human sarcomas, we identified fusion transcripts of platelet derived growth factor B and collagen genes that predict sensitivity to PDGFR inhibitors. Transcriptomic profiling grouped these canine STS tumors into 4 clusters, one PNST group (H1), and 3 FSA groups selectively enriched for extracellular matrix interactions and PDFGB fusions (H2), homeobox transcription factors (H3), and elevated T-cell infiltration (H4). This multi-omics approach provides insights into canine STS sub-types at a molecular level for comparison to their human counterparts, to improve diagnosis, and may provide additional targets for chemo- and immuno-therapy.

Gene fusions in superficial mesenchymal neoplasms: Emerging entities and useful diagnostic adjuncts

Cutaneous mesenchymal neoplasms are diagnostically challenging because of their overlapping morphology, and, often, the limited tissue in skin biopsy specimens. Molecular and cytogenetic techniques have identified characteristic gene fusions in many of these tumor types, findings that have expanded our understanding of disease pathogenesis and motivated development of useful ancillary diagnostic tools. Here, we provide an update of new findings in tumor types that can occur in the skin and superficial subcutis, including dermatofibrosarcoma protuberans, benign fibrous histiocytoma, epithelioid fibrous histiocytoma, angiomatoid fibrous histiocytoma, glomus tumor, myopericytoma/myofibroma, non-neural granular cell tumor, CIC-rearranged sarcoma, hybrid schwannoma/perineurioma, and clear cell sarcoma. We also discuss recently described and emerging tumor types that can occur in superficial locations and that harbor gene fusions, including nested glomoid neoplasm with GLI1 alterations, clear cell tumor with melanocytic differentiation and ACTIN::MITF translocation, melanocytic tumor with CRTC1::TRIM11 fusion, EWSR1::SMAD3-rearranged fibroblastic tumor, PLAG1-rearranged fibroblastic tumor, and superficial ALK-rearranged myxoid spindle cell neoplasm. When possible, we discuss how fusion events mediate the pathogenesis of these tumor types, and we also discuss the related diagnostic and therapeutic implications of these events.

Tyrosine kinase inhibitors versus radiation therapy in unresectable dermatofibrosarcoma protuberans (DFSP): A narrative systematic review

BACKGROUND

In unresectable dermatofibrosarcoma protuberans (DFSP), no clear guideline exists regarding the use of tyrosine kinase inhibitors (TKI) versus radiotherapy. This study reviews current literature regarding TKI and radiotherapy in unresectable DFSP.

METHODS

Following PROSPERO registration (CRD42021232508), a systematic literature search was performed including all studies reporting clinical results of TKI and/or radiotherapy in the treatment of unresectable DFSP. A narrative synthesis was used to compare patient characteristics, outcomes, and adverse effects.

RESULTS

Of 1345 screened studies, 14 were included for review. Patient age ranged 18-77 years and 55% were male. Radiotherapy patients exhibited lower grade disease than TKI patients. Overall clinical benefit following TKI ranged from 70% to 96%. Radiotherapy patients exhibited control or resolution on last follow-up in 90% of cases. Radiotherapy adverse effects were mild, while TKI adverse effects were more severe and managed with dose reduction.

CONCLUSION

TKI may be employed in unresectable DFSP of all histology types whereas radiation alone may be limited to low-grade and classic-type DFSP. TKI may cause more severe adverse effects compared to radiation alone.

Integrated analysis of canine soft tissue sarcomas identifies recurrent mutations in TP53, KMT genes and PDGFB fusions

Canine soft tissue sarcomas (STS) are a heterogenous group of malignant tumors arising from mesenchymal cells of soft tissues. This simplified collective of tumors most commonly arise from subcutaneous tissues, are treated similar clinically, and conventionally exclude other sarcomas with more definitive anatomical, histological, or biological features. Histologically, canine STS sub-types are difficult to discern at the light microscopic level due to their overlapping features. Thus, genomic, and transcriptomic profiling of canine STS may prove valuable in differentiating the diverse sub-types of mesenchymal neoplasms within this group. To this purpose we sought to characterize the transcript expression and genomic mutation profiles of canine STS. To delineate transcriptomic sub-types, hierarchical clustering was used to identify 4 groups with district expression profiles. Using the RNAseq data, we identified three samples carrying driver fusions of platelet derived growth factor B ( PDGFB ) and collagen genes. Sensitivity to imatinib was evaluated in a canine STS cell line also bearing a PDGFB fusion. Using whole exome sequencing, recurrent driver variants were identified in the cancer genes KMT2D (21% of the samples) and TP53 (21%) along with copy number losses of RB1 and CDKN2A. Gene amplifications and resulting transcript increases were identified in genes on chromosomes 13, 14, and 36. A subset of STS was identified with high T-cell infiltration. This multi-omics approach has defined canine STS sub-types at a molecular level for comparison to their human counterparts, to improve diagnosis, and may provide additional targets for therapy.

Genomic alterations of dermatofibrosarcoma protuberans revealed by whole-genome sequencing

Background

Dermatofibrosarcoma protuberans (DFSP) is a rare and marginal cutaneous sarcoma of intermediate‐grade malignancy, for which the genomic landscape remains unclear. Understanding the landscape of DFSP will help to further classify the genomic pathway of malignant development in soft tissue.

Objectives

To identify the comprehensive molecular pathogenesis of DFSP.

Methods

In this study, the comprehensive genomic features, with 53 tumour‐normal pairs of DFSP, were revealed by whole‐genome sequencing.

Results

The mutational signature 1 (C > T mutation at CpG dinucleotides) is featured in DFSP, resulting in higher mutations in DNA replication. Interestingly, the recurrence of DFSP is correlated with low tumour mutation burden. Novel mutation genes in DFSP were identified, including MUC4/6, KMT2C and BRCA1, and subsequently, three molecular subtypes of DFSP were classified on the basis of MUC4 and MUC6 mutations. Various structural aberrations including genomic rearrangements were identified in DSFPs, particularly in 17q and 22q, which cause oncogene amplification (AKT1, SPHK1, COL1A1, PDGFβ) or tumour suppressor deletion (CDKN2A/B). In addition to gene fusion of COL1A1‐PDGFβ [t(17;22)], we identified gene fusion of SLC2A5‐BTBD7 [t(1;14)] in DFSP through whole‐genome sequencing, and verified it experimentally. Enrichment analysis of altered molecules revealed that DNA repair, cell cycle, phosphoinositide 3‐kinase and Janus kinase pathways were primarily involved in DFSP.

Conclusions

This is the first large‐scale whole‐genome sequencing for DFSP, and our findings describe the comprehensive genomic landscape, highlighting the molecular complexity and genomic aberrations of DFSP. Our findings also provide novel potential diagnostic and therapeutic targets for this disease.

What is already known about this topic?

Chromosomal translocation between chromosome 17 and chromosome 22 is the main feature in the pathogenesis of dermatofibrosarcoma protuberans (DFSP).

What does this study add?

We describe the comprehensive genomic landscape of DFSP, highlighting the molecular complexity and genomic aberrations.

Our findings provide novel potential diagnostic and therapeutic targets for this disease.

What is the translational message?

Our study revealed novel molecular subtypes of DFSP based on genetic mutations, which benefits precision diagnosis.

We also found oncogene amplification, including AKT1 and SPHK1, which provides novel potential target molecules for further DFSP treatment.

In addition to gene fusion of COL1A1‐PDGFβ, we identified a novel gene fusion of SLC2A5‐BTBD7 in DFSP, which is a novel potential diagnostic and therapeutic target for this disease.

Immunotherapy in soft tissue sarcoma: current evidence and future perspectives in a variegated family of different tumour

INTRODUCTION

In the last few years steps forward in the knowledge of the biology of soft tissue sarcomas (STS) has led to the development of new therapeutic strategies, including immunotherapy.

AREAS COVERED

This review outlines the recent findings on immunological features and provides a synopsis of the results of clinical trials with different immunotherapy approaches in STS, discussing criticisms and how the efficacy of immunotherapy could be improved.

EXPERT OPINION

The heterogeneity of STS has limited generalized approaches of immunotherapy in the disease. Clinical decisions should encompass a comprehensive characterization of the tumour microenvironment (TME), marked by intra-histotype diversity. Profiling of immune cells, checkpoint molecules and antigen target/HLA expression is deemed to re-shape the classical histotype classification for a selection of the most appropriate immune-based treatment. In a synergistic view, tumour-directed treatments, designed on the genetic and epigenetic histotype make-up, should be monitored for their immunomodulant effect and applied to ensure or amplify immunotherapy response. In light of the dynamic nature of the TME, this immunomonitoring should be conducted at baseline and during treatment, for improved therapeutic decisions and rational sequence of treatment combination, pursuing an immunological marker approach by histotype guidance.

Advanced dermatofibrosarcoma protuberans: an updated analysis of cases from an Indian sarcoma clinic

AIM

Dermatofibrosarcoma protuberans (DFSP) accounts for less than 2% of all soft-tissue sarcomas.

PATIENTS & METHODS

We retrospectively reviewed our database for patients with locally advanced or metastatic DFSP who had presented to our clinic between January 2016 and January 2020.

RESULTS

We identified a total of 14 patients, of whom ten had sarcomatous transformation. Eleven cases had metastatic disease and three were locally advanced. The initial partial response rate to first-line imatinib was 76.9% and the overall median progression-free survival on imatinib was 15 months.

CONCLUSION

We had a high proportion of patients with sarcomatous transformation, in contrast to their relative rarity in the West. While most patients had initial good responses to imatinib, second-line therapies were not as effective.

Targeted and immuno-based therapies in sarcoma: mechanisms and advances in clinical trials

Sarcomas represent a distinct group of rare malignant tumors with high heterogeneity. Limited options with clinical efficacy for the metastatic or local advanced sarcoma existed despite standard therapy. Recently, targeted therapy according to the molecular and genetic phenotype of individual sarcoma is a promising option. Among these drugs, anti-angiogenesis therapy achieved favorable efficacy in sarcomas. Inhibitors targeting cyclin-dependent kinase 4/6, poly-ADP-ribose polymerase, insulin-like growth factor-1 receptor, mTOR, NTRK, metabolisms, and epigenetic drugs are under clinical evaluation for sarcomas bearing the corresponding signals. Immunotherapy represents a promising and favorable method in advanced solid tumors. However, most sarcomas are immune "cold" tumors, with only alveolar soft part sarcoma and undifferentiated pleomorphic sarcoma respond to immune checkpoint inhibitors. Cellular therapies with TCR-engineered T cells, chimeric antigen receptor T cells, tumor infiltrating lymphocytes, and nature killer cells transfer show therapeutic potential. Identifying tumor-specific antigens and exploring immune modulation factors arguing the efficacy of these immunotherapies are the current challenges. This review focuses on the mechanisms, advances, and potential strategies of targeted and immune-based therapies in sarcomas.

Molecular Determinants of Soft Tissue Sarcoma Immunity: Targets for Immune Intervention

Soft tissue sarcomas (STSs) are a family of rare malignant tumors encompassing more than 80 histologies. Current therapies for metastatic STS, a condition that affects roughly half of patients, have limited efficacy, making innovative therapeutic strategies urgently needed. From a molecular point of view, STSs can be classified as translocation-related and those with a heavily rearranged genotype. Although only the latter display an increased mutational burden, molecular profiles suggestive of an “immune hot” tumor microenvironment are observed across STS histologies, and response to immunotherapy has been reported in both translocation-related and genetic complex STSs. These data reinforce the notion that immunity in STSs is multifaceted and influenced by both genetic and epigenetic determinants. Cumulative evidence indicates that a fine characterization of STSs at different levels is required to identify biomarkers predictive of immunotherapy response and to discover targetable pathways to switch on the immune sensitivity of “immune cold” tumors. In this review, we will summarize recent findings on the interplay between genetic landscape, molecular profiling and immunity in STSs. Immunological and molecular features will be discussed for their prognostic value in selected STS histologies. Finally, the local and systemic immunomodulatory effects of the targeted drugs imatinib and sunitinib will be discussed.

Molecular Alterations in Pediatric Solid Tumors

Pediatric tumors can be divided into hematologic malignancies, central nervous system tumors, and extracranial solid tumors of bone, soft tissue, or other organ systems. Molecular alterations that impact diagnosis, prognosis, treatment, and familial cancer risk have been described in many pediatric solid tumors. In addition to providing a concise summary of clinically relevant molecular alterations in extracranial pediatric solid tumors, this review discusses conventional and next-generation sequencing-based molecular techniques, relevant tumor predisposition syndromes, and the increasing integration of molecular data into the practice of diagnostic pathology for children with solid tumors.

Next‑generation sequencing analysis reveals that MTH‑3, a novel curcuminoid derivative, suppresses the invasion of MDA‑MB‑231 triple‑negative breast adenocarcinoma cells

Triple‑negative breast cancer (TNBC) behaves aggressively in the invasive and metastatic states. Our research group recently developed a novel curcumin derivative, (1E,3Z,6E)-3-hydroxy-5-oxohepta-1,3,6-triene-1,7-diyl)bis(2‑methoxy-4,1‑phenylene)bis(3-hydroxy2-hydroxymethyl)-2‑methyl propanoate (MTH‑3), and previous studies showed that MTH‑3 inhibits TNBC proliferation and induces apoptosis in vitro and in vivo with a superior bioavailability and absorption than curcumin. In the present study, the effects of MTH‑3 on TNBC cell invasion were examined using various assays and gelatin zymography, and western blot analysis. Treatment with MTH‑3 inhibited MDA‑MB‑231 cell invasion and migration, as shown by Transwell assay, 3D spheroid invasion assay, and wound healing assay. The results of the gelatin zymography experiments revealed that MTH‑3 decreased matrix metalloproteinase‑9 activity. The potential signaling pathways were revealed by next‑generation sequencing analysis, antibody microarray analysis and western blot analysis. In conclusion, the results of the present study show that, MTH‑3 inhibited tumor cell invasion through the MAPK/ERK/AKT signaling pathway and cell cycle regulatory cascade, providing significant information about the potential molecular mechanisms of the effects of MTH‑3 on TNBC.

Imatinib inhibits the malignancy of hepatocellular carcinoma by suppressing autophagy

Hepatocellular carcinoma (HCC) is one of the most common cancers and is associated with high morbidity and mortality rates. Recent research indicated that imatinib, a selective tyrosine kinase inhibitor, suppressed the growth of hepatocellular carcinoma. However, the effect of imatinib on HCC and its mechanism remain under investigated. In this study, we demonstrated that imatinib inhibited the proliferation, migration and invasion of HCC cells in vitro and exerted antitumour effects on HCC xenografts in mice in vivo. Imatinib treatment decreased the phosphorylation of AKT and increased the levels of both p62 (protein sequestosome 1) and LC3 (microtubule-associated protein 1A/1B-light chain 3) in HCC cells and HCC xenografts. Scanning confocal microscopy analysis with a mRFP-GFP-LC3 reporter and transmission electron microscopy analysis revealed that imatinib suppressed the autophagic flux by obstructing the formation of autolysosomes. Moreover, imatinib reversed the autophagy induced by sorafenib, and combined treatment with imatinib and sorafenib exerted a synergetic effect in HCC cells compared with monotherapy. Our collective data suggested that imatinib may target HCC by acting as an inhibitor of both tyrosine kinase and autophagy; here, we propose that imatinib could be a promising therapeutic agent for HCC in the clinic.

Dermatofibrosarcoma Protuberans: A Clinicopathologic and Therapeutic Analysis of 254 Cases at a Single Institution

BACKGROUND

Dermatofibrosarcoma protuberans (DFSP) is a rare low-grade tumor that typically does not metastasize but often recurs. Fibrosarcomatous DFSP (FS-DFSP) is associated with a substantially higher rate of metastasis and a poorer prognosis.

OBJECTIVE

This study sought to investigate the epidemiological, histopathological, and clinical characteristics of DFSP, especially with a particular focus on FS-DFSP.

MATERIALS AND METHODS

Clinical data from 254 patients treated between January 1999 and July 2018 were retrospectively reviewed. Endpoints of the study were the incidence of significant disease-related clinical events.

RESULTS

Follow-up data from 211 patients were available for analysis, with a median follow-up time of 38 months (range: 1-196 months). The 5-year recurrence-free survival rate of patients underwent wide-local excision (WLE) was 97.1%. Patients underwent WLE exhibited a significantly decreased recurrence rate relative to patients treated through local excision (2.9% vs 37.7%; p < .001). Fibrosarcomatous DFSP had significantly higher rates of distant metastasis (66.7% [n = 4] vs 2.0% [n = 4]; p < .001) and long-term mortality (50.0% [n = 3] vs 1.5% [n = 3]; p < .001), compared with classical DFSP (C-DFSP).

CONCLUSION

Wide-local excision is an effective means of reducing DFSP recurrence. Rates of metastasis are higher for FS-DFSP than for C-DFSP, with the former having significantly poorer outcomes.

SMARCB1/INI1-deficient tumors of adulthood

The SMARCB1/INI1 gene was first discovered in the mid-1990s, and since then it has been revealed that loss of function mutations in this gene result in aggressive rhabdoid tumors. Recently, the term "rhabdoid tumor" has become synonymous with decreased SMARCB1/INI1 expression. When genetic aberrations in the SMARCB1/INI1 gene occur, the result can cause complete loss of expression, decreased expression, and mosaic expression. Although SMARCB1/INI1-deficient tumors are predominantly sarcomas, this is a diverse group of tumors with mixed phenotypes, which can often make the diagnosis challenging. Prognosis for these aggressive tumors is often poor. Moreover, refractory and relapsing progressive disease is common. As a result, accurate and timely diagnosis is imperative. Despite the SMARCB1/INI1 gene itself and its implications in tumorigenesis being discovered over two decades ago, there is a paucity of rhabdoid tumor cases reported in the literature that detail SMARCB1/INI1 expression. Much work remains if we hope to provide additional therapeutic strategies for patients with aggressive SMARCB1/INI1-deficient tumors.

Undifferentiated and dedifferentiated neoplasms of the female genital tract

Undifferentiated neoplasms in the female gynecologic tract comprise two main groups-undifferentiated carcinoma, most common in the endometrium and ovary, and undifferentiated uterine sarcoma, although tumors with an undifferentiated appearance may occur in all gynecologic organs. Their differential diagnosis is broad and generous sampling, careful morphological evaluation, judicious use of immunohistochemistry, and in many cases, molecular testing is often essential in the diagnostic work-up. As some of these neoplasms fail to respond to conventional chemotherapy regimens and/or radiation therapy, targeted therapy may be valuable in treating these highly aggressive tumors, thus the importance of precise diagnosis. In this review we discuss the clinicopathological features of undifferentiated carcinoma, dedifferentiated carcinoma, and undifferentiated uterine sarcoma, followed by a comprehensive analysis of morphological mimickers. Finally, we briefly review ovarian and lower genital tract tumors with an undifferentiated histological appearance.

NTRK and other recently described kinase fusion positive uterine sarcomas: A review of a group of rare neoplasms

The landscape of uterine sarcomas has greatly expanded in recent years to include neoplasms with recurrent gene fusions, such as BCOR and YWHAE translocated high-grade endometrial stromal sarcomas. Sophisticated molecular techniques have also resulted in the description of "new" entities associated with recurrent kinase fusions involving NTRK and RET as well as COL1A1-PDGFB rearranged uterine sarcomas. These rare neoplasms will be discussed in this review, highlighting that some of the underlying molecular events are clinically actionable and potentially susceptible to targeted therapy. While relatively few of these neoplasms have been described to date, likely being previously lumped under the spectrum of undifferentiated uterine sarcoma, the number of cases will expand in the future given their recognition and the increasing availability of molecular testing. These neoplasms have overlapping morphology (often with a "fibrosarcoma-like" appearance) and immunohistochemical features, and are characterized by variable clinical outcomes. Although immunohistochemistry may assist in some cases, a definitive subclassification requires confirmatory molecular studies. As these molecular assays may not be routinely available in most laboratories, referral to reference centers may be needed. In order to assist the pathologist, we suggest a diagnostic algorithm for routine practice when dealing with a malignant or potentially malignant uterine spindle cell neoplasm.

A Rare Malignant Disease, Dermatofibrosarcoma Protuberans of the Breast: A Retrospective Analysis and Review of Literature

Dermatofibrosarcoma protuberans (DFSP) is a rare low-grade fibroblastic mesenchymal tumor derived from the dermis. The aim of this retrospective analysis was to summarize the clinicopathological data from our cases and published cases to offer more evidence for the recognition of dermatofibrosarcoma protuberans (DFSP). A total of 6 breast DFSP patients who had received treatment in our hospital were retrospectively enrolled, and detailed clinicopathological data were gathered for analysis. The median age was 29.5 years (ranging from 17 to 42 years). Most cases presented a red or brown-red, mobile, well-circumscribed, protruding, breast mass (ranging from 1 to 3 cm). For histopathology, all cases (6/6) showed a storiform pattern of spindle cells that were positive for CD34 (6/6) and Vimentin (5/6) and negative for smooth muscle actin (0/6) and S-100 protein (0/6). The majority of patients (5/6) underwent wide local excision, with 2 cases treated with radiotherapy. With a median follow-up of 36 months, all 6 patients survived without recurrence or metastasis. The PubMed database was used to search for similar cases. Eventually, 36 cases were included in this review, while cases without detailed clinical information or not reported in English were excluded from the analysis. To summarize, DFSP of the breast is an extremely rare malignancy characterized by spindle tumor cells arranged in a storiform pattern and positivity for CD34. The core needle biopsy is one of the crucial methods for its preoperative diagnosis. Management of DFSP is mainly based on surgical excision. It is prone to local recurrence, so long-term follow-up is required.

Strategies for care of patients with gastrointestinal stromal tumor or soft tissue sarcoma during COVID-19 pandemic: A guide for surgical oncologists

The coronavirus disease-2019 (COVID-19) pandemic is deeply impacting the accessibility of cancer patients to surgery. In resource-limited conditions, the standard of care might not be deliverable, but evidence to support alternative management strategies often exists. By revisiting available treatment options, this review provides surgical oncologists with an evidence-based framework for treating patients with gastrointestinal stromal tumor, extremity/truncal soft tissue sarcoma, and retroperitoneal sarcoma to rapidly adapt their decision-making to the constant evolution of the COVID-19 pandemic.

A Multicenter Phase II Study of Pazopanib in Patients with Unresectable Dermatofibrosarcoma Protuberans

Dermatofibrosarcoma protuberans (DFSP) is a soft-tissue sarcoma characterized by a high risk of local infiltration. The identification of the COL1A1-PDGFB t(17;22) translocation activating the PDGF pathway led to the use of imatinib in unresectable DFSP, with a response rate of 36-80%. Pazopanib is a multitarget tyrosine kinase inhibitor approved for soft-tissue sarcomas. We conducted a phase II study of patients with unresectable DFSP to evaluate the efficacy and safety of pazopanib. Patients received 800 mg of pazopanib daily. The primary endpoint was the objective response rate defined as the reduction of the largest diameter of the tumor by ≥30% at 6 months or at surgery. A total of 23 patients, including one pretreated with imatinib, were enrolled. With a median follow-up of 6.2 months (interquartile range = 5.6-7.8 months), five patients (22%, 95% confidence interval = 7-22%) had a partial response to pazopanib. The best objective response rate was 30% (95% confidence interval = 13-53%) using Response Evaluation Criteria in Solid Tumors. One patient with metastatic DFSP previously treated with imatinib died after 2.4 months. Nine patients (39%) discontinued the treatment owing to adverse events. Pharmacodynamics analyses of tumor samples were conducted: the enrichment of EGF and the EGFR-associated gene panel was associated with resistance, suggesting that EGFR-targeted therapies could be a therapeutic option to explore in DFSP. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT01059656.

Identification of a survival-related signature for sarcoma patients through integrated transcriptomic and proteomic profiling analyses

Sarcoma (SARC) represents a group of highly histological and molecular heterogeneous rare malignant tumors with poor prognosis. There are few proposed classifiers for predicting patient's outcome. The Cancer Proteome Atlas (TPCA) and The Cancer Genome Atlas (TCGA) databases provide multi-omics datasets that enable a comprehensive investigation for this disease. The proteomic expression profile of SARC patients along with the clinical information was downloaded. 55 proteins were found to be associated with overall survival (OS) of patients using univariate Cox regression analysis. We developed a prognostic risk signature that comprises seven proteins (AMPKALPHA, CHK1, S6, ARID1A, RBM15, ACETYLATUBULINLYS40, and MSH6) with robust predictive performance using multivariate Cox stepwise regression analysis. Additionally, the signature could be an independent prognostic predictor after adjusting for clinicopathological parameters. Patients in high-risk group also have worse progression free intervals (PFI) than that of patients in low-risk group, but not for disease free intervals (DFI). The signature was validated using transcriptomic profile of SARC patients from TCGA. Potential mechanisms between high- and low-risk groups were identified using differentially expressed genes (DEGs) analysis. These DEGs were primarily enriched in RAS and MPAK signaling pathways. The signature protein molecules are candidate biomarkers for SARC, and the analysis of computational biology in tumor infiltrating lymphocytes and immune checkpoint molecules revealed distinctly immune landscapes of high- and low-risk patients. Together, we constructed a prognostic signature for predicting outcomes for SARC integrating proteomic and transcriptomic profiles, this might have value in guiding clinical practice.

Uterine mesenchymal tumours: recent advances

Almost all uterine mesenchymal tumours have been historically classified as either smooth muscle or endometrial stromal neoplasms. Recent application of molecular techniques has identified numerous lesions with distinctive genetic abnormalities and clinicopathological characteristics. Newly discovered uterine sarcoma subtypes include high-grade endometrial stromal sarcomas with BCOR genetic abnormalities, fibrosarcoma-like uterine sarcomas with NTRK rearrangements and COL1A-PDGFRB fusions, as well as undifferentiated uterine sarcomas with SMARCA4 mutations. Novel PLAG1 and PGR fusions have been identified in subsets of myxoid and epithelioid leiomyosarcomas. Some uterine tumours resembling ovarian sex-cord tumour harbour GREB1 and ESR1 rearrangements. Histological and immunophenotypical features as well as underlying genetic abnormalities defining these lesions are discussed.

Dermatofibrosarcoma Protuberans: Update on the Diagnosis and Treatment

Dermatofibrosarcoma protuberans (DFSP) is a slow growing, low- to intermediate-grade dermal soft-tissue tumor. It has a high local recurrence rate but low metastatic potential. It is characterized by a uniform spindle cell arrangement, classically with a storiform pattern and CD34 immunoreactivity. The histomorphology and immunophenotype overlap with a broad range of other neoplasms. The standard treatment is complete surgical excision. The surgical procedures include wide local excision (WLE) with tumor free margins, Mohs micrographic surgery (MMS) and amputation. Unresectable DFSPs are treated with radiation therapy and/or targeted therapy. DFSP has characteristic t(17; 22) (q22; q13), resulting in a COL1A1- PDGFB fusion transcripts in more than 90% of DFSPs. Molecular detection of the gene rearrangement or fusion transcripts is helpful for the diagnosis of patients with atypical morphology and for screening candidates for targeted therapy with tyrosine kinase inhibitors. The aims of the present review are to update the clinical presentation, tumorigenesis and histopathology of DFSP and its variants for diagnosis and differential diagnosis from other benign and malignant tumors, to compare the advantages and drawbacks of WLE and MMS, to propose the baseline for selecting surgical procedure based on tumor’s location, size, stage and relationship with surrounding soft tissue and bone structures, and to provide a biologic rationale for the systemic therapy. We further propose a modified clinical staging system of DFSP and a surveillance program for the patients after surgical excision.

Overview of « druggable » alterations by histological subtypes of sarcomas and connective tissue intermediate malignancies

We summarize herein the literature data about molecular targeted therapies in sarcomas and conjunctive tissue intermediate malignancies. For each clinical setting, the level of evidence, the mechanism of action and the target are described. The two major axes include (i) identification of subgroups of tumors with druggable alteration irrespective of the histological diagnosis (e.g. NTRK), and (ii) druggable target of pathway related to the physiopathology of the tumor: denosumab and bone giant cell tumor, imatinib and soft tissue giant cell tumor, mTOR inhibitor and PECOMA.

Clinical and pathological analysis of dermatofibrosarcoma protuberans with long-term follow-up

BACKGROUND

Dermatofibrosarcoma protuberans (DFSP) is a rare dermal sarcoma characterised by low-grade malignancy, slow infiltrative growth, local recurrence and rare distant metastases.

OBJECTIVE

Many international studies exist on DFSP, but limited data on Asian patients are available. This article fills this gap.

METHODS

A retrospective and observational patient series based on records of 99 patients diagnosed with DFSP and treated with wide local excision and assessments of complete circumferential peripheral and deep margin from 2002 to 2018. The margin width, pathological characteristics and surgical methods of 99 patients were described. Follow-up outcomes of 43 patients were evaluated.

RESULTS

In total, 106 DFSP resections were performed in 99 Asian patients (mean age: 44 years, SD: 14 years). Locations of DFSP are the trunk (63%), extremities (23%), head and neck (9%) and groin (5%). The average margin width was 3.5 ± 0.5 (SD) cm. CD34, vimentin and AOPD positivity was found in 98%, 100% and 86% of specimens, respectively. The median value of Ki67 expression was 5% + (range 1% + ∼ 50% +). Primary closure was used for 69% of all excisions, while flaps, grafts or other closures were used for the other excision procedures. A total of 43 patients were followed up for a mean duration of 53±36 (SD) months. Six patients exhibited recurrence. The eight-year recurrence-free survival rate was 94%.

CONCLUSION

Wide local excision and margin assessments can remove DFSP tumours and control recurrence.

Imatinib Treatment for Locally Advanced or Metastatic Dermatofibrosarcoma Protuberans: A Systematic Review

Importance

Dermatofibrosarcoma protuberans (DFSP) has the potential for local destruction and recurrence, although it carries a low risk of metastasis. Complete surgical resection with negative margins is considered the gold standard for treatment; however, there are cases that are unresectable owing to tumor extension or size or owing to risk of cosmetic and/or functional impairment. Imatinib treatment has been used for locally advanced or metastatic DFSP.

Objective

To evaluate the usefulness of imatinib for treating DFSP.

Evidence Review

We conducted a systematic review on the PubMed and Embase databases for articles published from September 2002 through October 2017 using the key words "dermatofibrosarcoma" or "dermatofibrosarcoma protuberans" AND "therapy" AND "imatinib." References within retrieved articles were also reviewed to identify additional studies. Studies of adults with histologically proven DFSP treated with imatinib as monotherapy or as an adjuvant or neoadjuvant therapy to surgery were included. Extracted data were analyzed using descriptive statistics. PRISMA guidelines were followed. All analysis took place October through December 2017.

Findings

Nine studies met inclusion criteria; 152 patients were included. The calculated mean patient age was 49.3 years (range, 20-73 years). Calculated mean tumor diameter was 9.9 cm (range, 1.2-49.0 cm). When COL1A1-PDGFβ protein translocation (collagen, type 1, alpha 1-platelet-derived growth factor β) was reported, it was present in 90.9% of patients (111 of 122). Complete response was seen in 5.2% of patients (8 of 152), partial response in 55.2% (84 of 152), stable disease in 27.6% (42 of 152), and progression in 9.2% (14 of 152). Four of the 152 patients (2.6%) were excluded from the analysis owing to unknown or unevaluable response. There were no differences in response rate using 400-mg or 800-mg daily doses (67.5% or 27 of 40 patients for 400-mg dose vs 67.1% or 49 of 73 patients for 800-mg dose complete or partial response; P > .99). Adverse events were present in at least 73.5% of cases (78 of 106); severe adverse events were present in 15.1% of cases (20 of 132).

Conclusions and Relevance

Imatinib is a useful directed therapy in patients with DFSP who are not surgical candidates owing to disease extension or significant cosmetic or functional impairment. There seems to be no difference between 400- or 800-mg daily doses.

Cutaneous soft tissue tumors: how do we make sense of fibrous and "fibrohistiocytic" tumors with confusing names and similar appearances?

In the 2018 World Health Organization Classification of Skin Tumors, a wide range of predominantly benign mesenchymal neoplasms are included in the fibroblastic, myofibroblastic, and "fibrohistiocytic" categories. By far the most common of these tumors is dermatofibroma (fibrous histiocytoma). There are many histologic variants of dermatofibroma, some of which (cellular, aneurysmal, and atypical) are associated with a higher risk of local recurrence; these variants may be mistaken for more aggressive tumor types, including sarcomas. Furthermore, distinguishing among the fibrous and "fibrohistiocytic" tumors can be a diagnostic challenge, given their sometimes-similar histologic appearances and confusing nomenclature. Immunohistochemistry and molecular genetic assays play a relatively limited role in the diagnosis of these tumor types, with notable exceptions (i.e., epithelioid fibrous histiocytoma and dermatofibrosarcoma protuberans). Proper recognition of dermatofibrosarcoma protuberans is critical, since this tumor type is associated with locally aggressive behavior; transformation to the fibrosarcomatous variant brings metastatic potential. In recent years, understanding of the molecular pathogenetic basis for cutaneous mesenchymal neoplasms has increased dramatically, with the discovery of gene rearrangements in some of these tumor types. In this review, the histologic features of the most common fibrous and "fibrohistiocytic" cutaneous mesenchymal neoplasms will be discussed, as well as recently identified molecular genetic alterations.

Imatinib prevents elastase-induced abdominal aortic aneurysm progression by regulating macrophage-derived MMP9

Abdominal aortic aneurysm (AAA) is characterized with progressive weakening and considerable dilation of the aortic wall. Despite the high risk of mortality in the elderly population, there are still no clinical pharmacological therapies to alleviate AAA progression. Macrophage-derived MMP9 acts as a key factor in extracellular matrix degradation and is crucial for aortic aneurysm development and aortic rupture. Here, we demonstrated that the transcription level of MMP9 was suppressed with a concentration-dependent manner in macrophages after Imatinib treatment, which was accompanied by the down-regulation of MMP9 protein expression and reduced MMP9 secretion in vitro. Imatinib administration (50 mg/kg/d, i.g.) was carried out one week after the establishment of elastase-induced AAA in rats, stabilizing aneurysm progression and improving survival rate via decreasing the aortic diameter and preventing elastin degradation. Expression and activity of MMP9 in the artery tissues were significantly suppressed after Imatinib treatment via in situ assessment like immunohistochemistry and zymography, although macrophage infiltration was not affected. Furthermore, we found that Imatinib inhibited MMP9 transcription through reduction of STAT3 phosphorylation and translocation from nucleus to cytoplasm. These observations indicated that Imatinib prevents aneurysm progression by inhibiting STAT3-mediated MMP9 expression and activation, suggesting a new application of Imatinib on AAA clinical therapy.

Dermatofibrosarcoma protuberans: surgical management of a challenging mesenchymal tumor

Introduction

Dermatofibrosarcoma protuberans (DFSP) is a rare, low-grade malignant mesenchymal tumor of the soft tissue, characterized by slow infiltrative growth and common local recurrence, with rare distant metastases.

Patients and methods

We present a retrospective study of nineteen patients who were diagnosed with DFSP and operated at our institution in > 10-year period. We examined the clinicopathological parameters with special emphasis on the margin status regarding the clinical outcome and the follow-up.

Results

A total of eight cases underwent re-excision at our institution following primary excision or incisional biopsy performed at a different institution. Seven cases received excision after incisional biopsy at our institution. Four patients developed recurrent disease following primary excision with histological R0 margins at other institutions and received re-excision at our institution. All excisions at our institution resulted in R0 margins with no recurrence recorded at last follow-up (6 to 175; mean 84 months). The mean margin for those who received resection at our institution was 1.67 cm. Negative margins upon primary excision were achieved using a mean margin width of 2.04 cm. Most common tumor localization was the trunk (10 cases).

Conclusion

Awareness of this rare entity is important for a prompt diagnosis and a proper management of the disease. The greatest clinical challenge in the management of DFSP is achieving local control. Complete excision of the tumor with surgical margin widths of at least 2 cm is recommended.

Using biology to guide the treatment of sarcomas and aggressive connective-tissue tumours

Sarcomas are a heterogeneous group of malignancies that arise from cells of a mesenchymal origin. Surgery forms the mainstay of the treatment of most patients with localized sarcoma and might be followed or preceded by chemotherapy and/or radiotherapy. In the metastatic setting, systemic treatments tend to improve survival and control symptoms. However, the adverse events and sometimes disappointing outcomes associated with these empirical approaches to treatment indicate a need for new approaches. The advent of next-generation sequencing (NGS) has enabled more targeted treatment of many malignancies based on the presence of specific alterations. NGS analyses of sarcomas have revealed the presence of many alterations that can be targeted using therapies that are already used in patients with other forms of cancer. In this Review, we describe the genomic alterations considered to define specific nosological subgroups of sarcoma and whose contribution to oncogenesis provides a biological rationale for the use of a specific targeted therapy. We also report several less successful examples that should guide researchers and clinicians to better define the extent to which the identification of driver molecular alterations should influence the development of novel treatments.

A novel MAP3K7CL-ERG fusion in a molecularly confirmed case of dermatofibrosarcoma protuberans with fibrosarcomatous transformation

Dermatofibrosarcoma protuberans (DFSP) is a translocation-associated, low-grade sarcoma with fibroblastic differentiation. It is the most common superficial sarcoma, almost exclusively arising within the dermis. In a minority of cases, there is a transition from the conventional morphology to a fibrosarcomatous pattern, known as a fibrosarcomatous DFSP (FS-DFSP). Although a number of different molecular alterations have been described to account for this transformation, it remains poorly understood. Herein we report the first case of a FS-DFSP with a fusion between ERG, an ETS family transcription factor, and MAP3K7CL, a kinase gene rarely observed in fusion gene events.

Fibrosarcomatous dermatofibrosarcoma protuberans from scar following trauma

Dermatofibrosarcoma protuberans (DFSP) is an uncommon soft tissue neoplasm of low metastatic potential notable for its progressive growth and high rate of local recurrence after surgical excision. Fibrosarcomatous transformation of DFSP (FS-DFSP) is a rare variant characterized by higher rates of local recurrence and metastasis. Trauma has been hypothesized as a potential risk factor for the development of DFSP, although clear evidence has been lacking. In this study, we report a case of FS-DFSP that was found arising from a previously stable scar following a traumatic injury. A 49-year-old male was diagnosed with keloid scars following a motor vehicle accident where he sustained trauma. 12 years later, a large tumor developed immediately after a second traumatic event to the primary scar. Pathology of the excisional biopsy specimen demonstrated FS-DFSP with focal areas consistent with keloid and hypertrophic scar. This observation demonstrates the development of DFSP from underlying scar following a clear history of trauma. Furthermore, it suggests trauma as a possible trigger for the fibrosarcomatous transformation of DFSP.

Systematic Review of the Current Status of Human Sarcoma Cell Lines

Sarcomas are rare mesenchymal malignant tumors with unique biological and clinical features. Given their diversity, heterogeneity, complexity, and rarity, the clinical management of sarcomas is quite challenging. Cell lines have been used as indispensable tools for both basic research and pre-clinical studies. However, empirically, sarcoma cell lines are not readily available. To understand the present status of sarcoma cell lines and identify their current challenges, we systematically reviewed reports on sarcoma cell lines. We searched the cell line database, Cellosaurus, and categorized the sarcoma cell lines according to the WHO classification. We identified the number and availability of sarcoma cell lines with a specific histology. We found 844 sarcoma cell lines in the Cellosaurus database, and 819 of them were named according to the WHO classification. Among the 819 cell lines, 36 multiple and nine single cell lines are available for histology. No cell lines were reported for 133 of the histological subtypes. Among the 844 cell lines, 148 are currently available in public cell banks, with 692 already published. We conclude that there needs to be a larger number of cell lines, with various histological subtypes, to better benefit sarcoma research.

Collagen Features of Dermatofibrosarcoma Protuberans Skin Base on Multiphoton Microscopy

Dermatofibrosarcoma protuberans is a rare, low-grade skin fibroblastic tumor which tends to recur locally due to its high misdiagnosis. Dermatofibrosarcoma protuberans usually spreads through the intracutaneous and subcutaneous layers into the deep dermis layer in which the main component is collagen. Therefore, alterations in collagen shape and content are important for accurate diagnosis of dermatofibrosarcoma protuberans. In this study, multiphoton microscopy was employed to observe normal human skin and dermatofibrosarcoma protuberans skin. Then, a centerline based on an algorithm that skeletonizes a binary image of fibers was applied to analyze collagen shapes in 2 types of skin. Then, collagen content, including intensity and density, was quantitatively obtained to demonstrate differences between the 2 skin types. Results indicate that collagen shape and density can be considered as auxiliary diagnostic parameters to improve the accuracy of dermatofibrosarcoma protuberans diagnosis.

[Perianal dermatofibrosarcoma protuberans: a case report, review and update]

Dermatofibrosarcoma protuberans is a low-grade sarcoma typically originating in the dermis but with local invasion of subcutaneous cell and muscle tissue. We report a case of perianal dermatofibrosarcoma protuberans in a 41-year-old male complaining of anal pain and constipation. To date, only two cases of perianal dermatofibrosarcoma protuberans have been reported. The unusual location hinders surgical treatment. The characteristic translocation t(17;22)(q22;q13) leading to the formation of COL1A1/PDGFβ fusion transcripts is not only of diagnostic value but also enables an alternative imatinib-based therapy in inoperable or metastatic cases. The pertinent literature is reviewed.

Establishment of novel patient-derived models of dermatofibrosarcoma protuberans: two cell lines, NCC-DFSP1-C1 and NCC-DFSP2-C1

Dermatofibrosarcoma protuberans (DFSP) is a common type of dermal sarcoma, characterized by the presence of the unique collagen type I alpha 1 chain (COL1A1)-PDGFB translocation, which causes constitutive activation of the platelet-derived growth factor β (PDGFB) signaling pathway. Patients with DFSP exhibit frequent local recurrence, and novel therapeutic approaches are required to achieve better clinical outcomes. Patient-derived cancer cell lines are essential in the preclinical research. Here, we established novel patient-derived DFSP cell lines from two patients with DFSP and designated these cell lines NCC-DFSP1-C1 and NCC-DFSP2-C1. Tumors of the two patients with DFSP had COL1A1-PDGFB translocations with distinct COL1A1 breakpoints, e.g., in exons 33 and 15, and the translocations were preserved in the established cell lines. NCC-DFSP1-C1 and NCC-DFSP2-C1 cells exhibited similar morphology and limited capability of proliferation in vitro, forming spheroids when seeded on low-attachment tissue culture plates. In contrast, NCC-DFSP1-C1 cells had considerably higher invasive capability than NCC-DFSP2-C1 cells. Overall proteome contents were similar between NCC-DFSP1-C1 and NCC-DFSP2-C1 cells. Notably, in vitro screening studies identified anticancer drugs that showed antiproliferative effects at considerably low concentrations in the DFSP cell lines. Bortezomib, mitoxantrone, ponatinib, and romidepsin were more cytotoxic to NCC-DFSP1-C1 cells than to NCC-DFSP2-C1 cells. These cell lines will be useful tools for developing novel therapeutic strategies to treat DFSP.

Alternative PDGFD rearrangements in dermatofibrosarcomas protuberans without PDGFB fusions

Dermatofibrosarcoma protuberans is underlined by recurrent collagen type I alpha 1 chain-platelet-derived growth factor B chain (COL1A1-PDGFB) fusions but ~ 4% of typical dermatofibrosarcoma protuberans remain negative for this translocation in routine molecular screening. We investigated a series of 21 cases not associated with the pathognomonic COL1A1-PDGFB fusion on routine fluorescence in situ hybridization (FISH) testing. All cases displayed morphological and clinical features consistent with the diagnosis of dermatofibrosarcoma protuberans. RNA-sequencing analysis was successful in 20 cases. The classical COL1A1-PDGFB fusion was present in 40% of cases (n = 8/20), and subsequently confirmed with a COL1A1 break-apart FISH probe in all but one case (n = 7/8). 55% of cases (n = 11/20) displayed novel PDGFD rearrangements; PDGFD being fused either to the 5' part of COL6A3 (2q37.3) (n = 9/11) or EMILIN2 (18p11) (n = 2/11). All rearrangements led to in-frame fusion transcripts and were confirmed at genomic level by FISH and/or array-comparative genomic hybridization. PDGFD-rearranged dermatofibrosarcoma protuberans presented clinical outcomes similar to typical dermatofibrosarcoma protuberans. Notably, the two EMILIN2-PDGFD cases displayed fibrosarcomatous transformation and homozygous deletions of CDKN2A at genomic level. We report the first recurrent molecular variant of dermatofibrosarcoma protuberans involving PDGFD, which functionally mimic bona fide COL1A1-PDGFB fusions, leading presumably to a similar autocrine loop-stimulating PDGFRB. This study also emphasizes that COL1A1-PDGFB fusions can be cytogenetically cryptic on FISH testing in a subset of cases, thereby representing a diagnostic pitfall that pathologists should be aware of.