Dermatofibrosarcoma protuberans (DFSP) is an uncommon cutaneous tumor that is usually low grade, except for the fibrosarcomatous variant (DFSP-FS). The authors conducted a study to compare the clinicopathological, immunohistochemical, genetic, and therapeutic features of DFSP and DFSP-FS. They reviewed the clinicopathological features for 63 DFSP and 12 DFSP-FS. Immunohistochemistry and multiplex reverse transcriptase-polymerase chain reaction were carried out using formalin-fixed, paraffin-embedded tissue using specific primers for collagen type I alpha 1 (COL1A1) and platelet-derived growth factor beta (PDGFB). The authors found that DFSP-FS was associated with tumor history longer than five years (P=.009), tumor size greater than 4 cm (P=.001), more stages of modified Mohs micrographic surgery (P=.005) than DFSP, expansive subcutaneous infiltration (P=.005), muscular invasion (P=.0001), absence of CD34 staining (P=.018), p53 positivity (P=.006), and increased proliferative activity (P=.004) compared with DFSP. The COL1A1-PDGFB fusion transcript was found in 100 percent of DFSP-FS and 72 percent of DFSP. No association was found between the various COL1A1-PDGFB fusion transcripts and the different histologic subtypes. Wide local excision (2 cm) was performed in 47 percent of cases and modified Mohs micrographic surgery in 53 percent. After a mean followup of 73 months (range, 21 to 235 months), six patients had local recurrence (five DFSP and one DFSP-FS) and one patient with DFSP-FS died of the disease. The only factor related to local recurrence was type of surgery; 17 percent had wide local excision and none had modified Mohs micrographic surgery (P=.006). The authors noted that their study was retrospective and that prospective studies are necessary to confirm their results. They concluded that their results support the contention that DFSP-FS reflects tumor progression in DFSP, with larger size, particular invasive patterns, p53 expression, and increased prolifera- tive activity. However, as with low-grade DFSP, appropriate surgery permits a tumor-free excision. COL1A1-PDGFB is a useful tool for diagnosing DFSP and, particularly, DFSP-FS.