Synonyms

DFSP

Category

Soft tissue

Behaviour

Intermediate

Gender

Both equally

Tissue of Origin

Fibrous

Epidemiology

• Intermediate-grade fibroblastic tumour of the dermis
• Incidence 0.8–5 per million
• Peak incidence 2nd–5th decades
• Fibrosarcomatous transformation in 10–15%

Clinical Features

• Slow-growing plaque-like or nodular skin lesion
• Variable colour: flesh-coloured, reddish-brown, violaceous
• Protuberant nodular growth over years
• Local recurrence characteristic - rarely metastasises

Location

• Trunk (most common: chest, abdomen, back)
• Proximal extremities
• Head and neck
• Dermis and subcutis - rarely deeper

Imaging

• CT/MRI: infiltrative soft tissue mass in dermis/subcutis
• MRI better delineates extent of infiltration
• Rarely imaged - primarily clinical diagnosis
• Fibrosarcomatous variant may show deeper extension

Pathology

• Monotonous spindle cells in storiform pattern
• CD34 positive, S100 negative
• Infiltrates subcutaneous fat in honeycomb pattern
• Fibrosarcomatous (FS-DFSP) variant: fascicular High-grade areas, CD34 may be lost

Genetics

• COL1A1-PDGFB fusion (t(17;22)(q21;q13)) - present in >90%
• Ring chromosome 17 and 22 or unbalanced translocation
• PDGFB overexpression drives tumour growth
• FS-DFSP: additional genomic complexity

Treatment

• Wide local excision with minimum 2–3 cm margins
• Mohs surgery for facial and special site lesions
• Imatinib: pre-operative (to downsize) or for unresectable/metastatic disease
• Radiotherapy for positive margins

Prognosis

• Excellent for localised disease - 10-year survival 99%
• Local recurrence 10–20% after standard excision (reduced with Mohs)
• Metastasis rare (5%), predominantly in FS-DFSP variant
• FS-DFSP has worse prognosis

Key Points

• COL1A1-PDGFB fusion is diagnostic and also a therapeutic target (imatinib)
• CD34 is Highly characteristic on IHC but lost in FS-DFSP
• Mohs surgery achieves best local control for facial lesions
• Imatinib is Highly effective for PDGFB-rearranged tumours

Workup - Blood Tests

FBC, U&E, LFTs - pre-operative baseline

Workup - Local Imaging

• MRI primary site - infiltrative superficial to deep dermal/subcutaneous mass; extensive subclinical extension
• Ultrasound - initial assessment of superficial lesion

Workup - Biopsy

• Core needle biopsy from most indurated/protuberant area
• Immunohistochemistry: CD34+ (strong, diffuse), PDGFRA+, factor XIIIa–
• COL1A1-PDGFB fusion (RT-PCR or FISH) - present in >90%; confirms diagnosis and predicts imatinib sensitivity
• Fibrosarcomatous transformation: loss of CD34, increased mitoses - must be reported

Workup - Staging

• CT chest - for fibrosarcomatous variant or if metastasis suspected
• No routine staging required for classic DFSP (metastasis rare <5%)

Workup - Other

• Mohs micrographic surgery or wide excision (2–3 cm margins) - MDT plan essential
• Imatinib (400–800 mg/day) for locally advanced/unresectable/metastatic disease - COL1A1-PDGFB fusion predicts response

Follow-up Summary

• Post-op visit at 6 weeks
• Year 1–2: 6-monthly clinical review; USS or MRI if recurrence clinically suspected
• Years 3–5: Annual clinical review; discharge at 5 years if no recurrence
• No CT chest surveillance required for confirmed DFSP (metastasis rare)
• Fibrosarcomatous (FS-DFSP) variant: escalate to High-grade STS protocol with CT chest surveillance
• Imatinib pre-op patients: imaging response assessment at 3 months; toxicity monitoring