Dermatofibrosarcoma Protuberans

Dermatofibrosarcoma protuberans is a low to intermediate grade cutaneous sarcoma arising from dermal fibroblasts. It makes up about 1% of soft tissue sarcomas, with an incidence of about 4 per million people a year, mostly at 20 to 50 years. Sites are the trunk (40 to 50%), proximal limbs and the head and neck.

More than 90% carry the COL1A1-PDGFB fusion from t(17;22), which drives PDGF receptor signaling and explains the response to imatinib.

Growth is slow and locally infiltrative, with finger-like extensions through dermis, fat, fascia and sometimes muscle and bone.

Metastasis is rare (under 5%), mainly after fibrosarcomatous transformation (10 to 20% of tumors), which also has higher local recurrence. Recurrence is 20 to 50% after narrow excision, and 1 to 6% after margin-controlled surgery.

Complications: recurrence, deep invasion and fibrosarcomatous progression.

• A slowly enlarging firm, indurated plaque, flesh-colored to red-brown or violaceous, which develops nodules (protuberans) after months to years
• Atrophic or morphea-like early plaques that are often misdiagnosed
• Usually painless, with ulceration and bleeding in late disease
• Red flags: rapid growth, new nodules in a long-standing plaque, a recurrence, a mass over 5 cm, and deep fixation

1. Punch or incisional biopsy that includes the dermis and subcutis (a 4 mm or larger punch). Histology: storiform spindle cells infiltrating fat in a honeycomb pattern. CD34 positive and factor XIIIa negative.
2. Molecular test: COL1A1-PDGFB by FISH or RT-PCR for equivocal biopsies and for imatinib planning.
3. MRI for large, deep, recurrent or head and neck tumors to define depth.
4. Chest imaging for fibrosarcomatous tumors, recurrences and large tumors.

Differentials: dermatofibroma, keloid, morphea, scar, epidermoid cyst, lipoma, atypical fibroxanthoma, other sarcomas.

• Surgery: margin-controlled excision.
  • Mohs micrographic surgery or slow Mohs with complete circumferential and deep margin assessment, preferred for the head, neck and sites where tissue is limited.
  • Wide local excision with 2 to 4 cm lateral margins to the deep fascia, with delayed closure until histology confirms clear margins.
  • Local anesthesia with lidocaine 1% with adrenaline 1:100,000 (maximum 7 mg/kg of lidocaine with adrenaline). Cefazolin 2 g IV before incision for flaps or grafts.
  • Reconstruct with skin graft or flap after margin clearance.
• Radiotherapy: 50 to 60 Gy in 25 to 30 fractions for positive margins that cannot be re-excised, and for unresectable disease.
• Imatinib for unresectable, recurrent, metastatic or neoadjuvant treatment: 400 mg orally once daily with food (800 mg a day in 2 divided doses for progression). Continue until response, which usually takes 3 to 6 months, then re-evaluate for surgery. Monitor blood count and liver tests every 2 weeks for the first month, and watch for edema, nausea, rash and cytopenias.
• Fibrosarcomatous and metastatic tumors: doxorubicin-based chemotherapy (doxorubicin 75 mg/m2 IV every 21 days), after imatinib failure.

Follow-up: clinical examination every 6 months for 3 years, then yearly for life, with MRI for suspected recurrence and chest imaging for high-risk tumors. Counsel on sun protection and on checking the scar monthly.