Definition/General
Introduction:
Dermatofibrosarcoma protuberans (DFSP) is a low-grade malignant soft tissue sarcoma
It constitutes 1-6% of all soft tissue sarcomas
It demonstrates local aggressive behavior with infiltrative growth
It shows low metastatic potential (rare)
It has characteristic t(17;22) translocation resulting in COL1A1-PDGFB fusion.
Origin:
Arises from dermal fibroblasts
Shows mesenchymal differentiation
Involves dermis and subcutis
May extend to superficial fascia
Origin possibly from CD34-positive dendritic cells
Shows infiltrative growth pattern through dermal collagen.
Classification:
WHO classifies as fibroblastic/myofibroblastic tumor
Classical DFSP (90% of cases)
Pigmented DFSP (Bednar tumor, 5-10%)
Myxoid DFSP (<5%)
Fibrosarcomatous DFSP (10-15%, high-grade transformation)
Giant cell fibroblastoma (juvenile form).
Epidemiology:
Peak incidence in 3rd-5th decades
Equal gender distribution
Most common on trunk (50-60%)
Proximal extremities (20-30%)
Rare in children except giant cell fibroblastoma
Indian population shows similar epidemiology to global patterns.
Clinical Features
Presentation:
Slowly enlarging skin nodule or plaque
Firm to indurated consistency
Red-brown to skin-colored
Irregular surface with possible protuberances
Non-tender lesion
May show multinodular configuration.
Symptoms:
Usually asymptomatic
Slow growth over months to years
Occasional mild discomfort
Change in size or color
Patients often report thickening of skin
May cause functional impairment in large lesions.
Risk Factors:
Previous trauma or burn (10-20% of cases)
Radiation exposure
Genetic predisposition (rare)
No strong association with UV exposure
Immunosuppression (rare association)
Most cases are sporadic.
Screening:
No specific screening guidelines
Clinical examination of suspicious lesions
MRI imaging for extent evaluation
Core biopsy for diagnosis
Multidisciplinary approach for treatment planning.
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Gross Description
Appearance:
Firm nodular or plaque-like lesion
Skin-colored to red-brown
Irregular surface with possible protuberances
Size typically 2-10 cm at diagnosis
Cut surface shows white-tan fibrous tissue.
Characteristics:
Well-demarcated but infiltrative margins
Multinodular configuration common
May show pigmentation (Bednar tumor)
Firm consistency throughout
Cut surface appears homogeneous and fibrous.
Size Location:
Size ranges from 1-20 cm (median 5 cm)
Most common on trunk (50-60%)
Proximal extremities (shoulders, thighs)
Head and neck (10-15%)
Scalp in pediatric cases.
Multifocality:
Satellite lesions due to infiltrative growth
Multifocal recurrence if incompletely excised
Local recurrence common (10-50% if margins positive)
Distant metastasis rare (<5%).
Microscopic Description
Histological Features:
Monomorphic spindle cells in storiform pattern
Uniform nuclei with minimal pleomorphism
Infiltrative growth through dermal collagen
Honeycomb pattern at periphery
Low mitotic rate (<4/10 HPF)
Entrapment of adnexal structures.
Cellular Characteristics:
Spindle-shaped cells with elongated nuclei
Minimal cytoplasm
Uniform nuclear morphology
Fine chromatin
Inconspicuous nucleoli
Rare mitotic figures
No significant pleomorphism.
Architectural Patterns:
Storiform (cartwheel) pattern characteristic
Honeycomb pattern at periphery
Infiltrative margins
Entrapment of fat and adnexal structures
Parallel orientation in some areas
Herringbone pattern in fibrosarcomatous areas.
Grading Criteria:
Low-grade sarcoma (classical DFSP)
Mitotic rate <4/10 HPF
High-grade transformation (fibrosarcomatous change)
Increased cellularity in high-grade areas
Mitotic rate >5/10 HPF in fibrosarcomatous areas.
Immunohistochemistry
Positive Markers:
CD34 (95-100% positive, strong and diffuse)
Vimentin (positive)
Apolipoprotein D (90% positive)
Factor XIIIa (subset positive)
Procollagen I (positive)
Nestin (subset positive).
Negative Markers:
Desmin (negative)
Smooth muscle actin (negative)
S-100 protein (negative)
Cytokeratins (negative)
CD68 (negative)
Factor VIII (negative)
EMA (negative).
Diagnostic Utility:
CD34 most important diagnostic marker
Strong diffuse positivity characteristic
Useful for differential diagnosis
Retained in recurrences
Lost in fibrosarcomatous transformation
Essential for challenging cases.
Molecular Subtypes:
COL1A1-PDGFB fusion (90-95% of cases)
t(17;22)(q22;q13) translocation
PDGFB overexpression
Ring chromosome 17 (rare)
Giant cell fibroblastoma shows similar genetics.
Molecular/Genetic
Genetic Mutations:
t(17;22)(q22;q13) translocation (90-95%)
COL1A1-PDGFB fusion gene
Supernumerary ring chromosomes (subset)
PDGFRA mutations (rare)
TP53 mutations (in fibrosarcomatous transformation)
CDKN2A deletions (high-grade areas).
Molecular Markers:
PDGFB protein overexpression
PDGF receptor alpha activation
COL1A1-PDGFB fusion transcript
CD34 expression
Cyclin D1 overexpression
Ki-67 low in classical type.
Prognostic Significance:
COL1A1-PDGFB fusion present in most cases
Ring chromosomes may indicate complex genetics
Fibrosarcomatous transformation associated with worse prognosis
High-grade areas increase metastatic risk
Margin status most important prognostic factor.
Therapeutic Targets:
Imatinib mesylate (PDGFR inhibitor)
Dasatinib (multi-targeted inhibitor)
Nilotinib (PDGFR inhibitor)
Pazopanib (multi-kinase inhibitor)
Targeted therapy for unresectable or metastatic disease.
Differential Diagnosis
Similar Entities:
Dermatofibroma (benign fibrous histiocytoma)
Solitary fibrous tumor (CD34 positive)
Fibrosarcoma (high-grade)
Neurofibroma (S-100 positive)
Leiomyosarcoma (smooth muscle markers)
Fibrous histiocytoma.
Distinguishing Features:
DFSP: CD34 strong positive
DFSP: Storiform pattern
DFSP: Infiltrative growth
Dermatofibroma: Factor XIIIa positive
SFT: CD34 positive but different morphology
Fibrosarcoma: CD34 negative
Neurofibroma: S-100 positive.
Diagnostic Challenges:
Distinguishing from dermatofibroma
Fibrosarcomatous DFSP vs fibrosarcoma
Myxoid DFSP variants
Superficial biopsy may miss diagnostic features
Recurrent lesions may show altered morphology
CD34 immunostaining essential.
Rare Variants:
Bednar tumor (pigmented DFSP with melanin)
Myxoid DFSP (myxoid matrix)
Giant cell fibroblastoma (pediatric variant)
Sclerotic DFSP (collagenous)
Granular cell DFSP (rare)
Pleomorphic DFSP (high-grade).
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
Wide local excision from [site], measuring [X x Y x Z] cm
Diagnosis
Dermatofibrosarcoma Protuberans
Histological Subtype
Subtype: [classical/pigmented (Bednar)/myxoid/fibrosarcomatous]
Microscopic Features
Shows uniform spindle cells in storiform pattern with infiltrative growth
Size and Depth
Tumor size: [X] cm; Depth: involves dermis and [extent]
Margins
Margins: [involved/uninvolved], closest margin [X] mm
Mitotic Rate
Mitotic rate: [X] mitoses per 10 HPF
Fibrosarcomatous Change
Fibrosarcomatous transformation: [present/absent]
Immunohistochemistry
CD34: [positive/negative]; [other markers]: [results]
Risk Assessment
Risk: [low/intermediate/high] based on subtype, margins, and fibrosarcomatous change
Final Diagnosis
Dermatofibrosarcoma Protuberans, [subtype], [risk level]