Periocular Cutaneous Soft-Tissue Giant Cell Tumor in a Pediatric Patient.

ABSTRACT: Giant cell tumor of soft tissue (GCTST) is a rare neoplasm genetically unrelated but histopathologically indistinguishable to its osseous counterpart. Histologically, GCTST is characterized as a multinodular proliferation of bland histiocytoid mononuclear cells intermixed with osteoclast-like giant cells. GCTST most commonly presents as a soft-tissue mass located in the extremities of middle-aged adults. In this report, we describe a case of a dermal GCTST arising in the periocular region of a 3-year-old girl. This is the youngest patient diagnosed with GCTST reported in the literature and is also singular because of its anatomic location: Only a handful of head and neck GCTSTs have been reported to date. Furthermore, GCTST most often presents as a superficial or deep soft-tissue mass and much less commonly as a dermal-based skin tumor, as was our case. On microscopic examination, the resected lesion demonstrated classical features including numerous osteoclast-like giant cells embedded in a background of mononuclear ovoid cells which displayed brisk mitotic activity and were surrounded by variable stromal hemorrhage. Tumor cells presented a vaguely fascicular arrangement. Immunohistochemical profile demonstrated positivity for smooth muscle actin and CD68 and negativity for desmin, myo-D1, S100, HMB-45, Melan-A, p16, and NKIC3. The unusual characteristics of this case emphasize the clinicopathologic heterogeneity of GCTST.