Overview
Low-grade fibromyxoid sarcoma (LGFMS) is a rare mesenchymal tumor characterized by its indolent yet potentially aggressive behavior, often masquerading as benign lesions due to its histological appearance. Primarily affecting young adults, LGFMS typically arises in the limbs and trunk but can occur in less common locations such as the thoracic cavity. Despite its low-grade histological features, LGFMS has a propensity for local recurrence and late metastasis, particularly to the lungs, which underscores the importance of vigilant long-term follow-up. Clinicians must maintain a high index of suspicion for LGFMS in patients presenting with persistent masses, especially when initial biopsies yield inconclusive results, as delayed diagnosis can significantly impact patient outcomes 13.Pathophysiology
LGFMS arises from genetic alterations primarily involving the fusion of the FUS and CREB3L2 genes, resulting from a t(7;16) translocation 23. This molecular aberration disrupts normal cellular processes, leading to uncontrolled proliferation and a fibroblastic phenotype characteristic of the tumor. Despite its genetic complexity, the initial clinical presentation often lacks aggressive features, complicating early diagnosis. Over time, however, the tumor can exhibit malignant behavior, including local invasion and distant metastasis, highlighting the need for thorough molecular characterization to guide management 23.Epidemiology
LGFMS is exceedingly rare, with incidence figures not extensively documented in large population studies. It predominantly affects young adults, with a slight male predominance observed in some case series 3. The tumor's distribution varies, with common sites including the deep soft tissues of the extremities and trunk, though rarer occurrences in atypical locations such as the thoracic cavity have been reported 13. Geographic and specific risk factors remain largely undefined, emphasizing the sporadic nature of the disease. Trends over time suggest no significant changes in incidence but highlight the importance of continuous surveillance and reporting to better understand its epidemiology 3.Clinical Presentation
Patients with LGFMS typically present with a slow-growing, painless mass, often in the deep soft tissues of the limbs or trunk. Atypical presentations can include intrathoracic masses, as seen in rare cases, which may mimic other thoracic pathologies 1. Red-flag features include rapid growth, pain, and signs of local invasion or distant metastasis, particularly to the lungs. The presence of hemangiopericytoma-like blood vessels, as noted in some cases, can further complicate the differential diagnosis, necessitating meticulous histopathological examination 4.Diagnosis
The diagnosis of LGFMS requires a comprehensive approach combining clinical suspicion, imaging, and definitive histopathological analysis. Key diagnostic steps include:Imaging: CT or MRI to assess tumor size, location, and potential invasion into adjacent structures 1.
Biopsy: Core needle biopsy or surgical excisional biopsy for histopathological examination 1.
Immunohistochemistry: Positive staining for MUC4 and other markers such as FUS fusion proteins 13.
Molecular Testing: Fluorescence in situ hybridization (FISH) or next-generation sequencing to detect FUS-CREB3L2 fusion genes 23.Specific Criteria and Tests:
Histopathology: Low-grade spindle cell morphology with focal nuclear atypia.
Immunohistochemistry: MUC4 positivity, often with additional markers like CD10 and BCL2.
Molecular Markers: Confirmation of FUS-CREB3L2 fusion through FISH or molecular sequencing.
Differential Diagnosis:
- Solitary Fibrous Tumor: Distinguished by CD34 positivity and absence of FUS-CREB3L2 fusion.
- Neurofibroma: Typically lacks MUC4 positivity and specific genetic fusions characteristic of LGFMS 34.Management
Initial Treatment
Surgical Resection:
Primary Approach: Wide local excision with clear margins is the mainstay of treatment 13.
Extent of Resection: Depending on local invasion, may include chest wall resection or lung resection in thoracic cases 1.Adjuvant Therapy:
Not Typically Required: For most cases, adjuvant radiotherapy or chemotherapy is not standard unless there are high-risk features such as incomplete resection or recurrent disease 2.Recurrent or Metastatic Disease
Re-resection: If feasible, surgical resection of recurrent or metastatic lesions is considered.
Systemic Therapy: Limited data; may include targeted therapies based on molecular profiles, though specific protocols are evolving 2.Monitoring and Follow-Up:
Regular Imaging: CT scans every 6-12 months for the first few years post-surgery.
Clinical Examination: Regular physical exams to monitor for local recurrence or new lesions.Complications
Local Recurrence: Common, necessitating close follow-up and prompt intervention if detected.
Metastasis: Particularly to the lungs, often occurring years after initial diagnosis; triggers include incomplete resection and genetic factors 13.
Peritoneal Dissemination: As seen in some cases, indicating aggressive behavior requiring multidisciplinary management 1.Prognosis & Follow-up
Prognosis for LGFMS varies widely, with early-stage disease generally having a better outcome. Key prognostic indicators include:
Tumor Location and Size: Thoracic and larger tumors correlate with worse outcomes.
Surgical Margins: Wide negative margins improve survival rates.
Molecular Profile: Presence of specific genetic alterations may influence behavior.Recommended Follow-up:
Initial Postoperative: Every 3-6 months for the first 2 years.
Subsequent: Annually for at least 5 years, adjusting based on clinical course and imaging findings 13.Special Populations
Elderly Patients: May present with atypical features; careful evaluation and multidisciplinary input are crucial 1.
Pediatrics: Rarely affected; when encountered, management parallels adult cases but with heightened vigilance for developmental impacts 3.
Comorbidities: Presence of other health issues may complicate surgical planning and postoperative care, necessitating tailored approaches 1.Key Recommendations
Suspect LGFMS in deep soft tissue masses with inconclusive initial biopsies, especially in young adults (Evidence: Moderate) 13.
Confirm diagnosis through comprehensive histopathological examination and molecular testing, including FISH for FUS-CREB3L2 fusion (Evidence: Strong) 23.
Perform wide local excision with clear margins for primary treatment (Evidence: Strong) 13.
Initiate regular long-term follow-up with imaging and clinical exams every 6-12 months for at least 5 years post-surgery (Evidence: Moderate) 13.
Consider re-resection for recurrent or metastatic disease if feasible, and explore emerging targeted therapies based on molecular profiles (Evidence: Weak) 2.
Monitor for peritoneal dissemination and lung metastases, particularly in cases with incomplete resection or atypical presentations (Evidence: Moderate) 1.
Tailor management in special populations, such as elderly patients and those with comorbidities, with multidisciplinary input (Evidence: Expert opinion) 1.
Utilize patient-derived cell lines like NCC-LGFMS1-C1 for advancing research and potential therapeutic targets (Evidence: Expert opinion) 2.
Differentiate from mimics such as solitary fibrous tumor and neurofibroma using immunohistochemical markers and molecular studies (Evidence: Moderate) 34.
Evaluate atypical presentations, including hemangiopericytoma-like vascular patterns, with caution and thorough diagnostic workup (Evidence: Moderate) 4.References
1 Narukami E, Anayama T, Yamamoto M, Bunno Y, Miyazaki R, Okada H et al.. Rapidly developing intrathoracic low-grade fibromyxoid sarcoma: A case report. Thoracic cancer 2023. link
2 Yoshimatsu Y, Noguchi R, Sin Y, Tsuchiya R, Ono T, Sei A et al.. Establishment and characterization of NCC-LGFMS1-C1: a novel patient-derived cell line of low-grade fibromyxoid sarcoma. Human cell 2021. link
3 Chien YC, Károlyi K, Kovács I. Paravertebral Low-grade Fibromyxoid Sarcoma with Supernumerary Ring Chromosome: Case Report and Literature Review. Annals of clinical and laboratory science 2016. link
4 Papp S, Dickson BC, Chetty R. Low-grade fibromyxoid sarcoma mimicking solitary fibrous tumor: a report of two cases. Virchows Archiv : an international journal of pathology 2015. link