All tumors were diffusely positive for vimentin and CD34 but negative for smooth muscle actin, desmin, epithelial membrane antigen, and cytokeratins; one pure adult-type DFSP was also S-100 protein positive; <1% of nuclei were Ki67 (Mib-1) positive.
The exact cell responsible for the development of a DFSP has been a matter of controversy for several decades; however, most histochemical and electron microscopic studies support a fibroblastic origin, with the tumor cells staining uniformly for vimentin and containing active endoplasmic reticulum synthesizing collagen.