Location: Trunk, groin, and proximal extremities.

Clinical: Nodular or plaque-like painless cutaneous tumor, slowly growing.

Diagnosis: A well-defined superficial tumor. On MRI, in T1 usually iso- or hypointense to skeletal muscle. In T2 intermediate or high signal intensity compared to fat. On STIR high signal, similar to water or blood vessels. Uniform enhancement of gadolinium.

Histopathology: DFSP: Monotonous spindle cell proliferation, diffusely infiltrating the dermis, subcutis, or both, spindle cells with elongated wavy nuclei. Cells are organized in a storiform pattern, there is minimal cellular atypia, and mitoses are rare. Characteristically there is infiltration of the subcutaneous fat in a honeycomb pattern. Giant-cell fibroblastoma: spindle to pleomorphic cells, variably collagenized matrix, multinucleated-appearing giant cells bordering pseudovascular spaces. Mitoses are rare and necrosis is absent. Fibrosarcomatous DFSP is defined by herringbone pattern and increased atypia and mitoses. On immunohistochemistry DFSP are positive for CD34. Apolipoprotein A1 has also been reported as a sensitive marker of DFSP. Giant-cell fibroblastoma: positive for CD34 and negative for S-100, CD31, and epithelial markers. DFSP and giant-cell fibroblastoma share similar molecular abnormalities: the presence of supernumerary ring chromosomes consisting of amplified sequences from chromosomes 17 and 22 and/or the presence of t(17;22), a balanced reciprocal translocation that results in the fusion of COL1A1, a gene of collagen, and PDGFβ, a gene that encodes a growth factor. Ring chromosomes are predominantly observed in DFSP of adult patients, whereas the t(17;22) translocation is mostly seen in DFSP of children and in giant-cell fibroblastoma.

Course and Staging: Conventional DFSP recurs locally in 10–50 % of cases, often after incomplete excisions. Distant metastases are observed in less than 5 % of cases, almost all of which are associated with high-grade fibrosarcomatous changes. Giant-cell fibroblastoma recurs in up to 50 % but does not metastasize. Recurrence rates are closely related to surgical margins.

Treatment: Wide excision with tumor-free margins is curative. Radiotherapy has been proposed for unresectable tumors or after margin-positive resections. Imatinib mesylate (Gleevec), a tyrosine kinase inhibitor, may have potential value in the treatment of recurrent or metastatic DFSP.