These lesions are typically poorly circumscribed with infiltration of the surrounding soft tissue structures. Histologically, DTs are composed of elongated, uniform, bland fibroblasts and myofibroblasts loosely arranged in sweeping bundles (Fig. 4a, b). Tumour cells are set within a collagenous to myxoid stroma
causing the lesion to closely resemble normal cellular fibrous tissue or scar. Keloid-like collagen or extensive hyalinization may be present. One of the most characteristic features of DTs is its vascularity with numerous blood vessels showing thick walls and open lumina. Mitotic figures are virtually absent. In fact, the observation of even a few mitotic figures should raise the suspicion of a low-grade fibrosarco-ma rather than DTs. On immunohistochemical analysis, tumour cells are generally positive for vimentin and actin. A few cells may also express desmin and S-100 protein. Ultrastructural studies further support the fibroblastic and myofibroblastic nature of DTs.
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