DFSP

Soft tissue

Intermediate

M = F

Fibrous

• Incidence 0.8-5 per million
• Peak incidence 2nd-5th decades
• Fibrosarcomatous transformation in 10-15%

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

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

• MRI: infiltrative soft tissue mass in dermis/subcutis with T1 isointensity and T2 hyperintensity
• Fibrosarcomatous variant may show deeper extension

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

• COL1A1-PDGFB fusion (t(17;22)(q21;q13))
• Ring chromosome 17 and 22 or unbalanced translocation

• 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

• 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

• Intermediate-grade fibroblastic tumour of the dermis
• "Honeycombing" of fat is a key pathologic feature
• Requires wide local excision to prevent recurrence. Mohs surgery achieves best local control for facial lesions
• Requires long-term follow up

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

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

• 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

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

• 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