What kind of tumor is dermatofibrosarcoma and how is it diagnosed and treated? Dermatofibrosarcoma of the bulge (DFSP) accounts for 2-6% of all soft tissue sarcomas and is an uncommon but not rare tumor. DFSP may arise from fibroblasts or histiocytes of the skin or both. The disease can occur at any age, but is most common in young and middle-aged adults. The malignancy of this disease is between dermatofibroma and malignant fibrous histiocytoma, and it is often inert and can develop insidiously for many years. DFSP initially appears as a limited raised sclerotic plaque located in the dermis. The lesion is usually solitary, red or cyanotic (or blue-purple) in color, and then slowly increases in size, followed by multiple nodules that are tough and firm, with a slightly shiny surface and adherence to the surface skin or subcutaneous tissue. Later, the surface skin can often atrophy and thinning or even sunken hair, capillary dilation can be seen, easy to break down, patients are generally asymptomatic, individual will have a slight discomfort. The disease is prone to recurrence if excision is incomplete, but the rate of distant metastasis is only 3%. DFSP can be divided into five types: 1) common type/classical type, which has a relatively good prognosis; 2) mucinous type; 3) fibrosarcoma type, which is mostly seen in patients with recurrent DFSP and has a relatively poor prognosis; 4) pigmented type; 5) others. The disease usually has a good prognosis if the surgery is complete, and distant metastases occur mostly in both lungs, and lymph node metastases are less common. DFSP needs to be differentiated from benign and malignant tumors such as dermatofibroma, cutaneous smooth muscle tumor, neurofibroma, sclerofibroma, nodular fasciitis and malignant fibrous histiocytoma. Surgery is the only means to cure DFPS. However, due to the rare and variable and atypical clinical manifestations of this disease, preoperative diagnosis is difficult, and it is often treated as a benign tumor for general local surgical excision in the outpatient clinic, resulting in irregular or incomplete surgical excision. Most of the DFSP at this time will recur, and it is also common to operate again after recurrence and get the correct diagnosis. There has been a lack of effective treatment for inoperable or recurrent metastatic DFSP. Radiotherapy is not very sensitive to this disease. It is now clear that the pathogenesis of the disease is a chromosome (17;22)(q22;q13) rearrangement that forms a COL1A1-PDGFB fusion gene, the expression product of which is a growth factor that keeps the relevant pathways on the surface of the tumor cells in a state of continuous activation, which in turn leads to the expansion of the tumor cells. This discovery has led to the introduction of the tyrosine kinase inhibitor imatinib mesylate into the treatment of this disease and has considerably changed the dilemma of no effective treatment for DFSP after recurrence and metastasis. Based on the excellent performance of imatinib mesylate in the treatment of this disease, the US FDA approved the drug in 2007 for the first-line treatment of unresectable, recurrent metastatic DFSP. It should be specifically noted that DFSP is largely negative for CD117, so detection of CD117 is not a prerequisite for the use of imatinib mesylate.