Is a dermatofibrosarcoma located in the deltoid region of the left shoulder considered an extremities sarcoma?

Classification of Dermatofibrosarcoma in the Deltoid Region

A dermatofibrosarcoma protuberans (DFSP) located in the deltoid region of the left shoulder is classified as an extremity sarcoma, not retroperitoneal. 1

Anatomical Classification Rationale

DFSP is categorized based on its anatomical location, with clear distinctions between:

• Extremity sarcomas: Include tumors of the upper and lower limbs, including the shoulder region
• Trunk sarcomas: Involve the chest wall, abdominal wall, and back
• Retroperitoneal sarcomas: Located in the retroperitoneal space behind the abdominal cavity

The deltoid region (p. deltoidei dorsi lat. sin.) is part of the upper extremity, specifically the shoulder area, making this DFSP an extremity sarcoma.

Staging and Treatment Implications

The classification as an extremity sarcoma has important treatment implications:

• Surgical approach: For extremity DFSP, complete surgical excision with negative margins is the primary treatment 1

  • Mohs micrographic surgery or other forms of peripheral and deep en face margin assessment (PDEMA) are preferred over wide local excision 1
  • For extremity locations, 2-4 cm margins to investing fascia are typically recommended when Mohs is not available 1

• Radiation considerations: If margins are positive or narrow after surgery, radiation therapy may be considered, with fields extending 3-5 cm beyond surgical margins 1

• Follow-up protocol: Regular follow-up every 6-12 months is recommended for all DFSP locations, with particular focus on the primary site 1

Molecular and Pathological Features

DFSP is characterized by:

• Translocation t(17;22)(q22;q13) resulting in COL1A1-PDGFB fusion gene in >90% of cases 1, 2
• CD34 immunoreactivity (typically positive) 1
• Factor XIIIa typically negative (helps differentiate from dermatofibroma) 1, 3

Treatment Algorithm for Extremity DFSP

1. Initial surgical approach:

   • Mohs micrographic surgery or PDEMA (preferred) 1
   • If unavailable, wide excision with 2-4 cm margins to investing fascia 1

2. Margin assessment:

   • If negative margins: Observation with follow-up every 6-12 months 1
   • If positive margins: Re-resection until margins are clear 1
   • If re-resection not possible: Consider radiation therapy (50-60 Gy) 1

3. For unresectable or metastatic disease:

   • Imatinib mesylate (if confirmed t(17;22) translocation) 1
   • Radiation therapy if not previously administered 1

Clinical Pearls and Pitfalls

• Pitfall: DFSP is frequently misdiagnosed due to inadequate tissue sampling. A punch or incisional biopsy that includes the subcutaneous layer is strongly recommended 1

• Caveat: Although classified as an extremity sarcoma, DFSP has unique biological behavior compared to other soft tissue sarcomas, with high local recurrence rates but low metastatic potential 2, 4

• Warning: Fibrosarcomatous transformation (FS-DFSP) is associated with more aggressive behavior and higher metastatic risk. The pathology report should note any such transformation 1

• Important: Reconstruction involving extensive undermining or tissue movement should be delayed until negative histologic margins are verified 1