Giant Cell Fibroblastoma

Definition

Superficial infiltrative soft tissue neoplasm characterized by irregular pseudovascular spaces lined by pleomorphic giant cells

Poorly circumscribed superficial soft tissue mass
- Most cases localized to subcutaneous tissue
  - Occasional involvement of dermis
  - Rare involvement of superficial underlying skeletal muscle
  - No deep visceral involvement reported
- Infiltrates between and around fat cells and adnexa
  - Produces “string of pearls” or “honeycomb” or “lace-like” patterns
Myxoid to hyalinized stroma with variable cellularity
Two cell populations
- Small bland spindled to stellate cells
  - Mild to moderate pleomorphism at most
- Scattered multinucleated giant cells
  - (Ultrastructure shows that they are actually just multilobated)
  - Vesicular nuclei with prominent nucleoli
- Infrequent mitotic figures
Irregular pseudovascular angiectoid spaces
- Partially lined by small stromal cells and giant cells
- No endothelial lining
Dermatofibrosarcoma protuberans is a closely related lesion
- More common in adult age group
- Mixtures may be seen
- Recurrences may be of the other neoplasm
- Same (17;22) translocation
Fibrosarcoma has not been reported in pure giant cell fibroblastoma
- May be seen in cases with a component of dermatofibrosarcoma protuberans
Occasional findings:
- Perivascular onion skin-like lymphocytic infiltrate
- Intralesional hemorrhage
- Myoid whorls
  - Small collections of actin positive cells with abundant cytoplasm

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342