Malignant giant cell tumor of the tendon sheath
Authors: Wu Nan‐Lin , Hsiao Pa‐Fan , Chen Be‐Fong , Chen Hsiu‐Chin , Su Hsin‐Yi 
Published: December 2003

A 27‐year‐old man presented with a slow‐growing, painless mass on the right anterior forearm of 4 years’ duration. Because of apparent rapid enlargement of the mass, he underwent surgical excision in a local clinic without histopathologic examination in June 1999. Recurrence of the tumor was noted in August 1999, when an excisional biopsy was performed. The pathologic diagnosis was giant cell tumor of the tendon sheath. In December 1999, he presented to our dermatology clinic with a local recurrence at the same site. He denied any history of trauma or any particular event preceding the initial appearance of the mass. On physical examination, there was a skin‐colored subcutaneous nodule, about 1.5 cm in size, under the operative scar on the right anterior forearm (Fig. 1). We performed an excisional biopsy. The pathology showed features of osteosarcoma. No bony involvement was seen on X‐ray or bone scan. Routine blood chemistry and blood count were normal.A subcutaneous nodule under the operative scar on the right forearmimageA wide excision was performed. Postoperatively, the patient was given six courses of radiotherapy (7020 cGy, cumulative dose), followed by chemotherapy consisting of six cycles of epirubicin. Follow‐up studies, including chest X‐ray and bone scan, did not show any evidence of metastasis or recurrence. He is currently well without recurrence, 2 years after treatment for the malignancy.On histopathologic examination, the biopsy specimen from August 1999 exhibited a somewhat nodular pattern. It was moderately cellular and composed of sheets of polygonal mononuclear cells with oval nuclei, which blended with stromal collagen. Many multinucleated giant cells of the osteoclast type were scattered throughout the lesion (Fig. 2a and 2b). Foci of xanthomatous change were seen at the periphery. These findings were consistent with a giant cell tumor of the tendon sheath. The recurrent tumor in December 1999 was a pseudoencapsulated nodular lesion with infiltration at the borders, and was mainly located in the subcutis with involvement of the dermis. Prominent cartilaginous tumor elements appeared in the center of the lesion (Fig. 3a). Abundant stream‐like tumor osteoid and ramifying bone formation were seen peripherally. The tumor was hypercellular and composed of irregular round or spindle cells with considerable pleomorphism and atypical mitoses (Fig. 3b). In addition, a varying number of giant cells with multiple bizarre nuclei or osteoclast‐like giant cells were present in some areas.(a) The lesion was composed of mononuclear cells and scattered multinucleated giant cells in a collagenous stroma (hematoxylin and eosin, × 100). (b) Higher magnification of the lesion in (a), showing osteoclast‐like giant cells with multiple, haphazardly distributed nuclei scattered among polygonal mononuclear cells (hematoxylin and eosin, × 200)image(a) Malignant cartilage formation (hematoxylin and eosin, × 200). (b) Atypical round or spindle cells with deposits of stream‐like osteoid shown in the top part of the figure (hematoxylin and eosin, × 200)imageThe pathology specimen from the wide excision was largely identical to the previous biopsy, and the surgical margins were free of tumor involvement.