DFSP-FS was associated with tumor history longer than 5 years (P = .009), tumor size greater than 4 cm (P = .001), more stages of modified Mohs micrographic surgery (P = .005), 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.
Furthermore, there was no difference in MSI status between an ordinary DFSP area and a fibrosarcomatous area in 7 tumors that exhibited both areas. p53 mutational analysis revealed 10 point mutations, composed of 4 missense mutations and 6 silent mutations, in 6 of 36 cases (16.7%).
Although DFSP has been classified in a category of fibrohistiocytic tumor of intermediate malignancy, the recurrent DFSP, DFSP-FS, and DFSP with aneuploidy and/or p53 overexpression could be a subgroup of DFSP with more aggressive clinical behavior than ordinary primary ones.
Although the number of cases examined is limited, the results suggest that alterations in the p53 pathway, such as overexpression of p53 protein by a mutated gene and mdm2 overexpression, are involved in fibrosarcomatous transformation in a subset of fibrohistiocytic tumours and possibly correlated with its more locally aggressive behaviour than that without p53 alterations or ordinary DFSP.
Four MFHs and nine other types of sarcoma (four leiomyosarcomas, two chondrosarcomas, one liposarcoma, one fibrosarcoma, and one dermatofibrosarcoma protuberans) showed nuclear positivity for p53.