Dermatofibrosarcoma protuberans (DFSP) is also known as progressive, recurrent dermatofibrosarcoma. The tumor has a high recurrence rate (20%-50%) but rarely metastasizes. It is predominantly seen in adults; it is more common in males than females; and it develops on the trunk. It is often associated with high CD34 expression;

Rhabdomyolysis cutaneous fibrosarcoma has a variety of morphologies, and the common ones include classic rhabdomyolysis cutaneous fibrosarcoma, pigmented rhabdomyolysis cutaneous fibrosarcoma, mucinous rhabdomyolysis cutaneous fibrosarcoma, rhabdomyolysis cutaneous fibrosarcoma with myxoid differentiation, plaque rhabdomyolysis cutaneous fibrosarcoma, and fibrosarcomatous rhabdomyolysis cutaneous fibrosarcoma. Especially in some rare subtypes (e.g., atrophic, plaque-like) subtypes, histologic diagnosis is difficult, and FISH probes can be a good aid to diagnosis;

Characteristic molecular genetic alteration of rhabdomyosarcoma and the closely related giant cell fibroblastoma: the presence of a large number of ring chromosomes formed by chromosome 17/22 forming the COL1A1-PDGFB fusion gene, an alteration that has not been detected in any other sarcoma.COL1A1-PDGFB gene fusion (t(17;22)(q21;q13)) It is most commonly seen in adults and has a high rate of recurrence after surgery. A large body of literature showed that 178 of 185 cases of confirmed pilonidal mutations were FISH-positive, 91% (104/114) of suspected cases (probable) were FISH-positive, and 81% (91/112) of possible cases (probable) were FISH-positive;

The COL1A1-PDGFB fusion gene is also seen in giant cell fibroblastoma, which supports the notion that giant cell fibroblastoma is the juvenile form of rhabdomyosarcoma;

The 2013 edition of the WHO classification classifies fibrosarcoma-type rhabdomyosarcoma as malignant (ICD-3).

Note: The ring chromosome COL1A1-PDGFB fusion gene is often accompanied by multicopy abnormalities, and FISH tends to show fusion signals other than 1 red, 1 green, and 2 yellow; the signals detected with the PDGFB breakage probe behave in a more simple and easily recognizable manner than the fusion probe.