Radiation Oncology/Sarcoma/DFSP

Dermatofibrosarcoma Protuberans

Epidemiology

• Cutaneous, locally aggressive, primarily low grade sarcoma
  • ~10% may contain a high-grade fibrosarcoma component
  • Low rate (<5%) of metastasis; higher if fibrosarcoma component
• Rare, 2-6% of soft tissue sarcomas
• Adults in 30's
• Risk factors: pregnancy, arsenic exposure, acanthosis nigricans

Clinical Presentation

• Plaque-like areas of cutaneous thickening
• Skin-colored, red-brown, or violaceous, particularly at the margins
• May arise within pre-existing scar or tattoo
• As it slowly enlarges, becomes raised ("protuberans"), firm, and nodular (fixed to dermis, but moves over deeper structures)
  • At diagnosis, >75% are superficial and <5cm diameter
• Slow, indolent growth, such that the lesion may be present for years
• Distribution:
  • Trunk ~50%
  • Lower extremity ~20%
  • Upper extremity 15%
  • Head and neck 15%

Work Up

• MRI helpful to estimate extent of deep extent
• CT not routinely necessary, unless bony invasion suspected
• Metastatic workup not routinely necessary, unless suspicion from H&P

Histology

• Cell of origina is not well understood
  • Histochemistry and electron microscopy suggest fibroblast lineage
  • However, the cells are CD34 positive, suggesting possibly dendritic lineage
  • In comparison, dermatofibromas and desmoid tumors are CD34-
• The tumors show benign-appearing spindle cells, in an irregular patterns resembling a straw mat. In early lesions there is a tumor-free zone with epidermis
• >90% have a t(17;22) translocation, resulting in a fusion of PDFG-B driven by a highly expressed collagen promoter (COL1A1)
  • Results in PDFGRb activation, which is tyrosine kinase receptor

Staging

• AJCC 7th Edition (2010)
  • First edition to include DFSP
  • Please see the Soft Tissue Sarcoma staging page

• American Musculoskeletal Tumor Society Staging for DFSP
  • Stage IA - Low or intermediate grade within the subcutaneous compartment
  • Stage IB - Low or intermediate grade extending outside anatomic compartment
  • Stage II - High grade histology

Natural History

• Tends to recur locally after excision alone
• Recur locally multiple times before metastasis; significant interval before development of metastases.
• Fibrosarcomatous changes predict for metastatic potential.

Treatment Overview

• Surgical resection is the primary treatment approach
  • Historically, wide local excision with 3cm margins was recommended, down to and including fascia
  • Mohs mapping reveals fine tentacles of tumor, and is becoming favored due to preservation of cosmesis
  • Some recommend modified Mohs to include a final path margin for permanent section
  • Pooled local recurrence rate with adequate margin WLE or Mohs' is <2%
  • Recurrences tend to occur within 3 years of surgery
• Definitive RT not routinely used; only couple reports available
• Adjuvant radiation is typically indicated if positive or close margin, or recurrent disease
• Given the high rate of t(17;22) leading downstream to a tyrosine kinase activation, efforts are under way to use Gleevec and other TKIs in this disease

Adjuvant Radiation Therapy

• MD Anderson; 1998 PMID 9531366 -- Ballo MT et al. "The role of radiation therapy in the management of dermatofibrosarcoma protuberans." Int J Radiat Oncol Biol Phys. 1998 Mar 1;40(4):823-7.
  • Retrospective. 19 patients receiving adjuvant xrt. 60 Gy given for +microscopic margin; 65 Gy given for gross residual disease. Local control at 10 yrs was 95%
  • Conclusion: adjuvant xrt should be considered for +margins or if adequate wide excision would lead to major cosmetic defect.

• Soft Tissue Tumours Working Group, The Netherlands Cancer Institute; 1997 PMID 9376187 -- Haas RL et al. "The role of radiotherapy in the local management of dermatofibrosarcoma protuberans."
  • 38 consecutive pts w/ DFSP. 21 tx'd surgically, 17 tx'd w/ combined modality.
  • Surgery alone had local control of 67%
  • Combined modality had local control of 82% (many of these who had xrt already had multiple local recurrences.

• Harvard; 1996 PMID 8708729 -- Suit H et al. "Radiation in management of patients with dermatofibrosarcoma protuberans." J Clin Oncol. 1996 Aug;14(8):2365-9.
  • 18 patients treated with postop (n=15) or definitive (n=3) xrt. Population was +/close margins or xrt alone.
  • Local control at 10yrs was 88%.