FIBROMA AND GIANT-CELL TUMOR OF TENDON SHEATH - A COMPARATIVE HISTOLOGICAL AND IMMUNOHISTOLOGICAL STUDY

Giant cell tumor of tendon sheath (GCTTS; ''nodular tenosynovitis'') a nd fibroma of tendon sheath (FTS) have traditionally been considered t o be two points in a single neoplastic continuum. However, no systemat ic studies have addressed this concept directly to date. To more clear ly define their relationship to one another, we studied five FTSs and seven typical GCTTSs by light microscopy and paraffin section immunohi stochemistry. Tissue samples were stained for vimentin, desmin, smooth muscle actin (SMA), S100 protein, leukocyte common antigen (CD45), CD 68 antigen (KP1), HAM56 antigen, alpha-1-antichymotrypsin (AACT), and MAC387 antigen. These reagents were chosen to address proposed ''fibro histiocytic'' and myofibroblastic lineages for the two lesions. All tu mors had a lobular appearance. GCTTS was more cellular than FTS; it co ntained conspicuous numbers of osteoclast-like cells, and the stroma w as not extensively hyalinized. In contrast, FTS was matrix-rich, often with extensive stromal sclerosis, and contained only rare giant cells . Immunophenotyping of GCTTS showed that both the spindle cell and gia nt cell components were positive for vimentin, LCA, CD68, HAM56, AACT, and MAC387, suggesting monocyte-macrophage-like features. Limited rea ctivity for desmin and SMA also implied conjoint myofibroblastic diffe rentiation. On the other hand, FTS showed focal staining with HAM56 (a ll cases) and for CD68 (one case); staining for vimentin and SMA was u niformly intense and diffuse. Based on these results, we conclude that GCTTS and FTS both exhibit varying degrees of monocyte-macrophage-lik e and myofibroblastic differentiation. The predominance of macrophage- related determinants in GCTTS and myofibroblastic markers in FTS suppo rts the premise that these lesions represent phenotypic extremes of a single clinicopathologic entity.