Definition/General
Introduction:
Fibrosarcoma is a malignant fibroblastic tumor
It represents 2-5% of adult soft tissue sarcomas
Shows fibroblastic differentiation with malignant features
FNAC demonstrates atypical spindle cells.
Origin:
Arises from fibroblasts in soft tissues
Can develop de novo or from pre-existing lesions
Deep soft tissues most common
May arise in radiation-induced or chronic osteomyelitis settings.
Classification:
WHO classification: Malignant fibroblastic tumor
Types: Adult fibrosarcoma
Infantile fibrosarcoma (ETV6-NTRK3)
Low-grade fibromyxoid sarcoma
Sclerosing epithelioid fibrosarcoma.
Epidemiology:
Adult type: 4th-6th decades
Equal gender distribution
Infantile type: First year of life
Rare tumor (<5% of sarcomas)
Extremities most common site.
Clinical Features
Presentation:
Enlarging mass
Painless initially
Deep-seated location
Firm consistency
Large size at presentation (>5 cm)
Rapid growth (high-grade).
Symptoms:
Mass effect symptoms
Pain in advanced cases
Functional limitation
Skin ulceration (large superficial)
Nerve compression
Systemic symptoms (metastatic).
Risk Factors:
Previous radiation (5-20 year latency)
Chronic osteomyelitis
Burn scars
Li-Fraumeni syndrome
Neurofibromatosis
Previous trauma (questionable).
Screening:
Imaging studies (MRI/CT)
FNAC/Biopsy for diagnosis
Staging workup
Chest imaging
Multidisciplinary evaluation
Genetic counseling if indicated.
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Gross Description
Appearance:
Gray-white, firm mass
Multinodular or lobulated
Whorled cut surface
Areas of necrosis (high-grade)
Hemorrhage variable
Poorly circumscribed.
Characteristics:
Fascicular pattern on cut surface
Firm to hard consistency
Heterogeneous appearance
Necrosis in high-grade tumors
Infiltrative margins
Variable vascularity.
Size Location:
Extremities (60%)
Trunk (25%)
Head/neck (10%)
Retroperitoneum (5%)
Size: Usually >5 cm
Can reach large dimensions (>15 cm).
Multifocality:
Usually solitary
Multifocal disease rare
Local recurrence common (30-50%)
Metastatic potential moderate to high
Lung metastases most common.
Microscopic Description
Histological Features:
FNAC shows atypical spindle cells
Nuclear pleomorphism
Hyperchromatic nuclei
Increased mitotic activity
Fascicular arrangement
Collagen production variable.
Cellular Characteristics:
Pleomorphic spindle cells
Elongated, atypical nuclei
Coarse chromatin
Prominent nucleoli
Moderate cytoplasm
Mitotic figures including atypical.
Architectural Patterns:
Cellular smears
Fascicular arrangement
Loosely cohesive
Individual cells predominant
Herringbone pattern (classic)
Necrotic background (high-grade).
Grading Criteria:
FNRS grading system
Differentiation (1-3 points)
Mitoses (1-3 points)
Necrosis (0-2 points)
Grade I: 2-3 points
Grade II: 4-5 points
Grade III: 6-8 points.
Immunohistochemistry
Positive Markers:
Vimentin - positive
CD34 - variable (30-50%)
Smooth muscle actin - focal positive
Muscle-specific actin - variable
Procollagen - positive
Type I collagen - positive.
Negative Markers:
S-100 protein - negative
Desmin - negative
Cytokeratin - negative
EMA - negative
MyoD1 - negative
CD117 - negative.
Diagnostic Utility:
Vimentin confirms mesenchymal origin
Negative neural/epithelial markers important
CD34 variable expression
Ki-67 correlates with grade
p53 may be overexpressed.
Molecular Subtypes:
Adult fibrosarcoma: Vimentin+, CD34 variable
Infantile fibrosarcoma: ETV6-NTRK3 fusion
Low-grade fibromyxoid sarcoma: MUC4+
Sclerosing epithelioid: EWSR1-CREB3L1.
Molecular/Genetic
Genetic Mutations:
Complex karyotype (adult type)
TP53 mutations
RB1 alterations
ETV6-NTRK3 fusion (infantile)
FUS-CREB3L2 (low-grade fibromyxoid)
EWSR1-CREB3L1 (sclerosing epithelioid).
Molecular Markers:
Chromosomal instability
p53 pathway disruption
RB pathway alterations
High mutational burden
DNA repair defects
NTRK fusions (infantile).
Prognostic Significance:
Grade determines prognosis
Low-grade: Better outcome (70-80% 5-year survival)
High-grade: Poor prognosis (30-50%)
Size >5 cm: Worse outcome
Deep location: Higher risk.
Therapeutic Targets:
Anthracycline-based chemotherapy
Ifosfamide combinations
NTRK inhibitors (infantile with fusion)
Pazopanib (advanced disease)
Immunotherapy (investigational).
Differential Diagnosis
Similar Entities:
Fibroma
Malignant peripheral nerve sheath tumor
Leiomyosarcoma
Synovial sarcoma
Spindle cell carcinoma
Dermatofibrosarcoma protuberans.
Distinguishing Features:
Fibrosarcoma: Vimentin+, herringbone pattern, no specific markers
MPNST: S-100+ focal, nerve association
Leiomyosarcoma: SMA+, desmin+
Synovial sarcoma: TLE1+, t(X;18)
Spindle cell carcinoma: Cytokeratin+
DFSP: CD34+ diffuse.
Diagnostic Challenges:
Distinguishing from other spindle cell sarcomas
Grade assessment on cytology
Fibroma vs low-grade fibrosarcoma
Subtype classification
Sampling adequacy.
Rare Variants:
Myxoid variant
Epithelioid areas
Giant cell variant
Inflammatory variant
Sclerosing type.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
Fine needle aspiration from [site], [size] cm soft tissue mass
Clinical History
[age]/[sex] with [duration] history of enlarging firm mass at [site]
Microscopic Examination
Cellular smears showing atypical spindle cells with nuclear pleomorphism, hyperchromatic nuclei, and increased mitotic activity. Fascicular arrangement noted. [Necrosis present/absent].
Immunocytochemistry
Vimentin: Positive, S-100: Negative, Desmin: Negative, Cytokeratin: Negative, Ki-67: [%]
Cytological Diagnosis
Cytological features consistent with FIBROSARCOMA, Grade [I/II/III]
Comments
Histopathological examination recommended for definitive grading. Molecular studies may be helpful. Multidisciplinary sarcoma team evaluation advised.