Figure 1: Features of the lesion: a vast, osteocondensant lesion of the pelvic bones associated with osteo-calcific degeneration of the peri- and paraosteal tissues (A, arrow). PAS diastase stain (B) underlines a lacelike osteoid bone matrix, produced by a highly cellular neoplasm. Detail of atypical tumor cells (C), strongly and diffusely positive for CD56 (D). Virtually all tumor cell nuclei are positive for p53 (E). B-E: Original Magnification x 400; B: PAS after diastase digestion; C-E: immunohistochemistry with diaminobenzidine chromogen.