WELL-DIFFERENTIATED ADULT-TYPE FIBROSARCOMA ARISING FROM THE OCCIPITAL SUBCUTANEOUS TISSUE IN A 17-YEAR-OLD MAN - CASE-REPORT WITH IMMUNOHISTOCHEMICAL STUDY

We report a case of a 17-year-old man with a spindle cell tumor in the occipital subcutaneous tissue. The enucleated tumor, measuring 2.5 x 2.0 x 1.0 cm, had a broad-bean shape and well circumscribed border and was localized to the subcutis without dermal involvement. Microscopic ally, the tumor was composed of uniform spindle cells showing interlac ing bundle formation and a herringbone pattern. The neoplastic cells w ere separated by collagen fibers in parallel fashion, the amount of wh ich varied with different areas in the tumor. Mitotic figures were eig ht mitoses per 50 high-power fields in number. The neoplastic cells we re positive for vimentin, Factor-XIIIa, alpha-smooth muscle actin and CD34, but negative for desmin, calponin, high molecular weight caldesm on, smooth muscle myosin heavy chain, collagen type IV, laminin and S- 100 protein. These immunohistochemical results indicated that the neop lastic cells showed differentiation toward fibroblasts/myofibroblasts/ dendritic interstitial cells. Although more than 50% of the neoplastic cells were positive for CD34, the present tumor should be diagnosed a s well differentiated fibrosarcoma, adult type, rather than extrapleur al solitary fibrous tumor and fibrosarcomatous areas of dermatofibrosa rcoma protuberans, on the basis of routine microscopic findings mentio ned above.