Malignant Adipose Soft Tissue Tumors. Immunohistochemical findings. (A) Immunohistochemically, the tumor cells are positive for CD34. (B) The mature adipose tissue within the solitary fibrous tumor is positive for S-100.Malignant fat-forming solitary fibrous tumor of the thigh. Noh SJ, Jang KY - Korean journal of pathology (2014). Not Altered. CC