Abstract

Giant cell tumor of soft parts (GCT-ST) is a rare benign entity that can occur anywhere but most commonly occurs on the extremities. We report on an 18-year-old young woman with primary breast GCT-ST. She was initially referred to plastic surgery for a painless ‘sebaceous cyst’ on the right upper breast that had been there for approximately one year. It was initially treated with Kenalog (triamcinolone acetonide) injections, but the lesion continued to grow. The mass was excised, and grossly had a rubbery, pale-tan multilobulated appearance that was not consistent with a sebaceous cyst. Histologically, the mass is a well defined lesion in the reticular dermis, composed of sheets of histoid-appearing cells with scattered multinucleated giant cells resembling osteoclast-like giant cell tumor of bone (GCT). There are areas of cytological atypia and occasional mitotic figures. Immunohistochemical staining was diffusely positive for CD68 and p63 with no significant staining for Pancytokeratin, S100, CD34, MART1, muscle specific actin, Desmin, H3.3g34W, CD1a, SOX10, Cytokeratin AE1/AE3, Cytokeratin 903, Cytokeratin 5/6, and Cam 5.2. The histologic features in conjunction with the immunohistochemical stains, were most consistent for GCT-ST. Although histologically similar to giant cell tumor of bone, GCT-ST does not harbor the same H3F3A mutation as in GCT of bone, where H3.3g34w stain would be positive. While GCT-ST is a rare occurrence, it is even more uncommon in the breast. We report on an extremely rare case of GCT-ST within the dermis.

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