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

Comprehensive Clinicopathological and Multiomics Characterization of Dermatofibrosarcoma Protuberans Revealed PDGFD Fusion as Distinct Molecular Subtype with Better Survival

Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive superficial mesenchymal neoplasm characterized by COL1A1::PDGFB fusion. Recently, PDGFD has been identified as a less common fusion partner. However, the clinicopathological and molecular differences between PDGFD and PDGFB fusion DFSP remain largely unknown. In this study of 363 DFSPs, we found 10 cases with PDGFD fusion, including two with a previously undescribed partner involving the EMILIN1 gene. Multi-omics analysis showed distinct transcriptomics, epigenomics, and copy number features for PDGFD fusion DFSP versus PDGFB fusion DFSP. PDGFD fusion DFSP had higher PDGFD expression and virtually no PDGFB expression. Both clustered into the DFSP epigenomic cluster but formed a distinct sub-cluster with differential methylation affecting fibroblast migration genes. Copy number analysis revealed that PDGFD fusion DFSP formed a distinct subgroup with a generally copy number neutral profile and better survival compared to PDGFB fusion DFSP that was dominated by amplification at translocation sites in chromosomes 17 and 22. Pooled analysis of 39 cases (incorporating 29 from the literature) revealed that PDGFD fusion DFSP was more common in females (71.8% vs. 42.4%, p <0.001), occurred at a lower age (Median 37 vs. 45, p < 0.01), and had a higher chance of occurrence at the breast (25.6% vs. 2.3%; p < 0.001). PDGFD fusion DFSP also tended to centre predominantly in the subcutis (63.6% vs. 30%; p < 0.001), had a circumscribed border (50% vs. 19.2%, p < 0.001), was smaller in size (3 cm vs. 3.5 cm, p = 0.017), and had a lower mitotic count (Median 1 vs. 3 per 10 h.p.f., p = 0.03). Overall, our study provided detailed multi-omics characterization of PDGFD fusion DFSP with significant clinico-pathological and diagnostic implications.

Fibrosarcomatous Dermatofibrosarcoma Protuberans With COL1A1-PDGFB Fusion in a 2-Year-Old Child: A Rare Occurrence With Spectrum of Histopathological Findings and Review of Literature

Dermatofibrosarcoma protuberans (DFSP) is an intermediate-grade fibroblastic neoplasm commonly seen in young and middle-aged patients and rarely in pediatric patients. Fibrosarcomatous transformation is common in adults but extremely uncommon in children. Here, we present a case of a 2-year-old child who presented with a progressively enlarging subcutaneous mass in the knee. Histopathological examination revealed a spindle cell tumor with a storiform and fascicular pattern. Immunohistochemistry showed variable cluster of differentiation 34 (CD34) expression, with positivity in storiform areas and negativity in fascicular regions. Next-generation sequencing confirmed the diagnosis by detecting a collagen type I alpha 1 (COL1A1)-platelet-derived growth factor subunit B (PDGFB) fusion, with the PDGFB breakpoint in exon 2 (chromosome 22) and COL1A1 in intron 47 (chromosome 17). This case represents only the fifth reported instance of fibrosarcomatous DFSP in a child under 10 years old. While wide local excision remains the standard treatment for DFSP, targeted therapy with imatinib may be considered for unresectable, recurrent, or metastatic cases, though guidelines for pediatric patients are not yet established. This case highlights the importance of molecular testing in confirming the diagnosis of rare pediatric soft tissue tumors and contributes to the limited literature on fibrosarcomatous DFSP in very young children.

Genomic Profiling Uncovers a Broader Spectrum of Dermatofibrosarcoma Protuberans: Implications for Diagnosis and Therapy

Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive cutaneous neoplasm driven by PDGFB or, rarely, PDGFD gene fusions. In some cases, DFSP progresses to a fibrosarcomatous form with metastatic potential, which may respond to tyrosine kinase inhibitors. This study explores whether comprehensive genomic profiling can reveal a broader clinical, anatomic, and pathologic spectrum for DFSP. Using the database of a large tumor sequencing reference laboratory, we identified tumors with PDGFB or PDGFD fusions and reviewed their histologic features, clinical information, exome sequencing data, and copy number alterations. Statistical significance was determined using Mann-Whitney U and Fisher exact tests. A total of 59 cases with PDGFB or PDGFD fusions were identified: 55 COL1A1::PDGFB, 3 EMILIN2::PDGFD, and 1 COL1A2::PDGFB. The cohort included 51 primary tumors and 8 metastases (31 males, 28 females, median age 49 years). Primary tumors were mainly located in the skin and soft tissues, including 35 in the trunk, 9 in the head and neck, and 9 in the extremities. Additionally, 6 tumors arose in visceral organs (4 in the uterus, 1 in the cervix, and 1 in the lung). Among cases with slides available for pathology review, 21 were classified as classic DFSP and 31 as fibrosarcomatous-DFSP (FS-DFSP). Notably, 21 tumors (36%) were initially misclassified, often due to atypical locations or histology. FS-DFSPs displayed a higher incidence of genomic alterations beyond PDGFB/PDGFD (75% vs 23.8%; P = .0005), including TERT promoter and NF1 variants, and demonstrated a significantly elevated tumor mutational burden (P = .0037) and TERT mRNA expression (1.27 vs 0.13 transcripts per million; P < .0001) compared with classic DFSPs. These findings underscore the value of genomic profiling for recognizing FS-DFSPs with unusual clinical or histologic features, particularly in guiding targeted therapy. Furthermore, by identifying molecular features specific to fibrosarcomatous variants, such as TERT reactivation, this study offers insights into potential molecular drivers of tumor progression in DFSP.

Dermatofibrosarcoma protuberans with PDGFD rearrangements: a case series featuring a novel EMILIN1::PDGFD fusion and comprehensive literature review

Dermatofibrosarcoma protuberans (DFSP) is a locally infiltrative mesenchymal neoplasm usually characterized by a COL1A1::PDGFB fusion. A minority of DFSPs have recently been shown to harbor alternative fusions, involving the PDGFD gene. The aim of this case series and literature review is to highlight the clinicopathologic and molecular features of PDGFD-rearranged DFSPs. Eighteen patients (twelve females and six males) with PDGFD-rearranged DFSPs were collected from the authors' institutional archives. Eight (44%) cases harbored a COL6A3::PDGFD fusion, five (28%) an EMILIN2::PDGFD fusion, and two (11%) an EMILIN1::PDGFD fusion. In three (17%) cases, the fusion partner was unknown. A literature review revealed 29 additional cases. Cumulatively, four alternative fusion genes have been detected: COL6A3::PDGFD (24/47, 51%), EMILIN2::PDGFD (12/47, 26%), EMILIN1::PDGFD (2/47, 4%), and TNC::PDGFD (1/47, 2%). In eight (17%) cases, the fusion partner was unknown. Most (20/24, 83%) COL6A3::PDGFD-fused DFSPs occurred in females with only four (17%) cases described in males. Additionally, half of them (12/24, 50%) developed in the breast/chest wall. EMILIN2::PDGFD-fused DFSPs often occurred in males, were located in the extremities (9/12, 75%), exhibited fibrosarcomatous transformation (9/12, 75%), were confined exclusively or primarily to the subcutis (10/12, 83%), and had a well-circumscribed contour (10/12, 83%). Specific molecular alterations in DFSPs correlate with certain clinicopathologic features. Notably, EMILIN2::PDGFD-fused DFSPs have a slight predilection for males, develop almost exclusively in the subcutis, tend to be well-circumscribed, and often exhibit fibrosarcomatous transformation, while COL6A3::PDGFD-fused DFSPs might have a predilection for the breast/chest wall of female patients. To the best of our knowledge, this is the first report of EMILIN1::PDGFD-fused DFSP.

Diagnosis and treatment of dermatofibrosarcoma protuberans. European interdisciplinary guideline - update 2024

Dermatofibrosarcoma protuberans (DFSP) is a cutaneous fibroblastic tumour that is locally aggressive, with a tendency for local recurrence, but rarely metastasizes. A collaboration of multi-disciplinary experts from the European Association of Dermato-Oncology (EADO), the European Dermatology Forum (EDF), the European Union of Medical Specialists (UEMS) and the European Academy of Dermatology and Venereology (EADV) was formed to update recommendations on DFSP diagnosis and treatment, based on current literature reviews and the experts' consensus. Diagnosis is suspected clinically and confirmed by pathology report, which should specify whether a transformation in higher-grade fibrosarcoma occurred. Detection of specific chromosomal translocations and/or fusion gene transcripts is useful to confirm diagnosis. Treatment is mainly surgical, intending to achieve complete resection of the tumour. To reduce the recurrence rate, the treatment of choice in DFSP is micrographically controlled surgery. Standard excision with a lateral safety margin of 2-3 cm is an acceptable alternative where only standard histopathological procedures are available. Imatinib is approved in Europe for treating inoperable primary tumours, locally inoperable recurrent disease, and metastatic DFSP. Use of imatinib has also been reported in extensive, difficult-to-operate tumours for preoperative reduction of tumour size, but clinical trials or large register data are required to confirm the usefulness of this approach. Therapeutic decisions for patients with fibrosarcomatous DFSP should be primarily made by an interdisciplinary oncology team ('tumour board').

Hotspots and future trends of dermatofibrosarcoma protuberans

Objective

Dermatofibrosarcoma protuberans (DFSP) is a moderately malignant soft tissue sarcoma with localized infiltrative growth. The extensive surgical scope and high recurrence rate of DFSP brings dysfunctional, aesthetic, psychological and economic problems to patients. The aim of this study is to explore the global publication characteristics, research hotspots and future trends of DFSP over the past 32 years via an intuitive visualized way.

Methods

The Web of Science Core Collection (WoSCC) database was searched for papers related to DFSP published from 1990 to 2022. Then bibliometric analysis of these publications was performed, including collaborative networks, co-citation analysis of journals and references, and cluster analysis of keywords.

Results

A total of 1588 papers were retrieved between 1990-2022. The United States was the most prolific country, followed by China. The article Imatinib Mesylate in Advanced Dermatofibrosarcoma Protuberans: Pooled Analysis of Two Phase II Clinical Trials, received most citations. Research hotspots and future trends are mainly focused on disease diagnosis, COL1A1-PDGFB fusion gene, drug and surgical treatment, fibrosarcomatous transformation, and immunotherapy.

Conclusion

The research on DFSP faces several clinical challenges. This study provides novel insights into future research directions and scientific decisions for DFSP.

Update on cutaneous mesenchymal tumors in the 5th edition of WHO classification of skin tumors with an emphasis on new fusion-associated neoplasms

The section on mesenchymal tumors in the 5th edition of WHO classification of skin tumors has undergone several changes, the most important of which is the inclusion of newly identified tumor entities, which will be the main focus of this review article. These specifically include three novel cutaneous mesenchymal tumors with melanocytic differentiation, and rearrangements of the CRTC1::TRIM11, ACTIN::MITF, and MITF::CREM genes as well as EWSR1::SMAD3-rearranged fibroblastic tumors, superficial CD34-positive fibroblastic tumors, and NTRK-rearranged spindle cell neoplasms. Some of the other most important changes will be briefly mentioned as well.

Molecular pathways and therapeutic strategies in dermatofibrosarcoma protuberans (DFSP): unravelling the tumor's genetic landscape

Dermatofibrosarcoma Protuberans (DFSP) is a rare soft tissue sarcoma distinguished by its infiltrative growth pattern and recurrence potential. Understanding the molecular characteristics of DFSP is essential for enhancing its diagnosis, prognosis, and treatment strategies. The paper provides an overview of DFSP, highlighting the significance of its molecular understanding. The gene expression profiling has uncovered unique molecular signatures in DFSP, highlighting its heterogeneity and potential therapeutic targets. The Platelet-Derived Growth Factor Receptors (PDGFRs) and Fibroblast Growth Factor Receptors (FGFRs) signaling pathways play essential roles in the progression and development of DFSP. The abnormal activation of these pathways presents opportunities for therapeutic interventions. Several emerging therapies, i.e., immunotherapies, immunomodulatory strategies, and immune checkpoint inhibitors, offer promising alternatives to surgical resection. In DFSP management, combination strategies, including rational combination therapies, aim to exploit the synergistic effects and overcome resistance. The article consisting future perspectives and challenges includes the discovery of prognostic and predictive biomarkers to improve risk stratification and treatment selection. Preclinical models, such as Patient-derived xenografts (PDX) and genetically engineered mouse models, help study the biology of DFSP and evaluate therapeutic interventions. The manuscript also covers small-molecule inhibitors, clinical trials, immune checkpoint inhibitors for DFSP treatment, combination therapies, rational therapies, and resistance mechanisms, which are unique and not broadly covered in recent pieces of literature. See also the graphical abstract(Fig. 1).

Spindle cell neoplasms with novel LTK fusion - Expanding the spectrum of kinase fusion-positive soft tissue tumors

AIMS

Kinase fusion-positive soft tissue tumors represent an emerging, molecularly defined group of mesenchymal tumors with a wide morphologic spectrum and diverse activating kinases. Here, we present two cases of soft tissue tumors with novel LTK fusions.

METHODS AND RESULTS

Both cases presented as acral skin nodules (big toe and middle finger) in pediatric patients (17-year-old girl and 2-year-old boy). The tumors measured 2 and 3 cm in greatest dimension. Histologically, both cases exhibited bland-looking spindle cells infiltrating adipose tissue and accompanied by collagenous stroma. One case additionally displayed perivascular hyalinization and band-like stromal collagen. Both cases exhibited focal S100 staining, and one case had patchy coexpression of CD34. Targeted RNA-seq revealed the presence of novel in-frame MYH9::LTK and MYH10::LTK fusions, resulting in upregulation of LTK expression. Of interest, DNA methylation-based unsupervised clustering analysis in one case showed that the tumor clustered with dermatofibrosarcoma protuberans (DFSP). One tumor was excised with amputation with no local recurrence or distant metastasis at 18-month follow-up. The other case was initially marginally excised with local recurrence after one year, followed by wide local excision, with no evidence of disease at 10 years of follow-up.

CONCLUSIONS

This is the first reported case series of soft tissue tumors harboring LTK fusion, expanding the molecular landscape of soft tissue tumors driven by activating kinase fusions. Furthermore, studies involving a larger number of cases and integrated genomic analyses will be warranted to fully elucidate the pathogenesis and classification of these tumors.

Platelet-Derived Growth Factor-D Fusion-Positive Dermatofibrosarcoma Protuberans: Case Report of an Atypical Breast Mass and Literature Review

Dermatofibrosarcoma protuberans (DFSP) is a rare, CD34+ mesenchymal neoplasm that classically involves the dermis. A COL1A1::PDGFB t(17;22) translocation is present in 91.4% to 96% of cases, resulting in aberrant proliferation due to tyrosine kinase hyperactivity. Here, we present a postmenopausal woman with a CD34-positive spindle cell neoplasm of the breast without cutaneous involvement, lacking muscle marker expression, STAT6 expression, and 13q14 deletion by fluorescence in situ hybridization (FISH). Although the classic PDGFB translocation was not detected by FISH, the overall features were highly suspicious for DFSP. Subsequent RNA-based next-generation sequencing revealed an EMILIN2::PDGFD fusion. A literature review showed that PDGFD fusions can be detected in up to 55% PDGFB FISH negative cases, with EMILIN2::PDGFD fusion highly associated with fibrosarcomatous transformation. This holds important diagnostic and prognostic information as fibrosarcomatous-DFSP is associated with higher recurrence and metastatic potential. The tumor was completely resected with clear margins, showed no fibrosarcomatous areas, and no evidence of recurrence is documented 2 years since resection. This review and case report adds to the literature regarding PDGFD-translocation positive DFSP as a differential diagnosis of CD34-positive spindle cell tumors of the breast, while emphasizing the prognostic importance of EMILIN2::PDGFD fusions.

An update on selected cutaneous (myo) fibroblastic mesenchymal tumors

Cutaneous (myo)fibroblastic tumors constitute a group of tumors with overlapping clinicopathological features and variable biologic behavior. In the present review we focus on the histomorphology, immunohistochemical profile and molecular background of the following entities: dermatofibrosarcoma protuberans (DFSP), CD34-positive fibroblastic tumor (SCD34FT), myxoinflammatory sarcoma (MIFS), low-grade myofibroblastic sarcoma, solitary fibrous tumor and nodular fasciitis. Although some of these entities typically arise in deep-seated locations, they may occasionally present as cutaneous/superficial tumors and might be challenging to recognize. This review covers in depth the latest advances in molecular diagnostics and immunohistochemical markers that have significantly facilitated the correct classification and diagnosis of these neoplasms.

Pediatric dermatofibrosarcoma protuberans: A clinicopathologic and genetic analysis of 66 cases in the largest institution in Southwest China

Background

Dermatofibrosarcoma protuberans (DFSP) is an uncommon cutaneous tumor in children. Most published articles are sporadic or small series and lack systematically molecular analyses. The aim of our study is to better understand the clinicopathologic and genetic features of these rare lesions.

Methods

All patients diagnosed with DFSP aged ≤ 18 years were retrospectively reviewed from January 2006 to May 2022.

Results

A total of 66 cases (32 male and 34 female patients) were identified, with ages ranging from 0.3 to 18 years (median, 13 years). Tumor locations predominantly occurred on the trunk (38/66, 57.6%), followed by the extremities (20/66, 30.3%) and head/neck (8/66, 12.1%). Histological findings revealed classic (41/66, 62.1%), myxoid (4/66, 6.1%), pigmented (6/66, 9.1%), plaque-like (3/66, 4.5%), giant cell fibroblastoma (GCF; 6/66, 9.1%), and fibrosarcomatous (6/66, 9.1%) variants of DFSP. Immunochemistry revealed minority tumors (9/66, 13.6%) showing patchy or negative staining for CD34. Fluorescence in situ hybridization (FISH) indicated that 49 of 53 tested cases including all detected biopsy specimens (11/11) contained COL1A1-PDGFB fusion, in which the average copy number gain of COL1A1-PDGFB was 0.68. There were four cases negative for COL1A1-PDGFB rearrangement, one of which was found to harbor a novel COL3A1-PDGFB fusion by next-generation sequencing (NGS). Treatment for 63 patients comprised 40 marginal excisions and 23 wide local excisions (WLEs), including 1 with imatinib therapy. Follow-up information was available on 49 patients with a duration of 12-161 months (median, 60 months). Fourteen patients developed tumor recurrence, all with initial marginal excisions. The others survived with no evidence of disease.

Conclusions

This study of pediatric DFSP indicates certain discrepancies in clinicopathologic characteristics between children and adults. The majority of pediatric DFSPs contain COL1A1-PDGFB fusion, the same as their adult counterparts. The COL3A1-PDGFB chimerism might be associated with the special morphology of GCF, which needs further investigation. FISH is valuable in biopsy tissues and cases with atypical CD34 immunostaining, while supplementary NGS could be helpful to identify the cytogenetically cryptic DFSP. Overall, an urgent accurate diagnosis is needed to formulate an optimal therapeutic strategy in the pediatric population.

Proteomic profiling of canine fibrosarcoma and adjacent peritumoral tissue

Fibrosarcoma (FSA) are rare soft tissue tumors that display aggressive local behavior and invasive growth leading to high rates of tumor recurrence. While the low incidence in humans hampers detailed understanding of the disease, FSA are frequent in dogs and present potential models for the human condition. However, a lack of in-depth molecular characterization of FSA and unaffected peritumoral tissue (PTT) in both species impedes the translational potential of dogs. To address this shortcoming, we characterized canine FSA and matched skeletal muscle, adipose and connective tissue using laser-capture microdissection (LCM) and LC-MS/MS in 30 formalin-fixed paraffin embedded (FFPE) specimens. Principal component analysis of 3'530 different proteins detected across all samples clearly separates the four tissues, with several targets strongly differentiating tumor from all three PTTs. 25 proteins were exclusively found in tumor tissue in ≥80% of cases. Among these, CD68 (a macrophage marker), Optineurin (OPTN), Nuclear receptor coactivator 5 (NCOA5), RAP1GDS1 (Rap1 GTPase-GDP dissociation stimulator 1) and Stromal cell derived factor 2 like 1 (SDF2L1) were present in ≥90% of FSA. Protein expression across all FSA was highly homogeneous and characterized by MYC and TP53 signaling, hyperactive EIF2 and immune-related changes as well as strongly decreased oxidative phosphorylation and oxidative lipid metabolism. Finally, we demonstrate significant molecular homology between canine FSA and human soft-tissue sarcomas, emphasizing the relevance of studying canine FSA as a model for human FSA. In conclusion, we provide the first detailed overview of proteomic changes in FSA and surrounding PTT with relevance for the human disease.

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.

A PHF1-TFE3 fusion atypical ossifying fibromyxoid tumor with prominent collagenous rosettes: Case report with a brief review

Ossifying fibromyxoid tumor (OFMT) is a rare mesenchymal neoplasm of uncertain line of differentiation that can be subdivided into typical, atypical, and malignant tumors. Cytogenetically, OFMT is characterized by recurrent gene rearrangement involving PHF1 in up to 85% of cases. The most common PHF1 fusion partner is EP400, present in approximately half of cases. Most recently, a novel fusion of PHF1-TFE3 was identified in about 10% of PHF1-rearranged OFMTs. Herein, we report a unique case of PHF1-TFE3 fusion atypical OFMT with prominent collagenous rosettes. A 50-year-old male patient presented with a slowly growing, painless mass in the right foot for 4 years. Gross examination showed a 3.5-cm, subcutaneous well-circumscribed, lobulated mass. Microscopic examination revealed a well-demarcated but un-encapsulated tumor without a peripheral bony shell. The neoplasm was composed of mildly atypical spindle to ovoid cells with increased mitosis (2 mitoses per 10 high-power fields) arranged in a multinodular manner within a fibromyxoid stroma, which contained numerous small, irregular collagenous rosettes surrounded by radiating growth of tumor cells. The neoplastic cells were diffusely positive for TFE3 and CD10. RNA sequencing revealed an in-frame fusion between PHF1 exon 12 and TFE3 exon 7. Subsequent Fluorescence in-situ hybridization analyses demonstrated positive for rearrangements of both the PHF1 and TFE3 loci. The patient was free of disease at 63 months' follow-up. Our case exhibits atypical features and prominent collagenous rosettes, expanding the morphological spectrum of OFMT with PHF1-TFE3 fusion.