Giant cell tumors of tendon sheath: a single and multiple immunostaining analysis.

Nineteen giant cell tumors of tendon sheath (GCTTS) were studied to elucidate the origin of the proliferating cells of these tumors, using single and multiple immunostaining techniques with a labeled avidin-biotin [LAB] method in paraffin-embedded tissues. Proliferating cell nuclear antigen (PCNA) and Ki-67 (MIB-1) antigen were present in mononuclear cells (PCNA 26%; MIB-14%) but were absent in giant cells. These findings indicate that mononuclear cells, but not giant cells, participate in the proliferative compartment of GCTTS. A histiocytic marker, HAM56, was positive in many mononuclear cells (mean 81%), but was totally negative in osteoclastic giant cells. Another histiocytic antigen, CD68, was expressed in both mononuclear cells (mean 28%) and most of the giant cells (mean 89%). By triple immunostaining for PCNA, HAM56 and vimentin, 83% of PCNA-positive mononuclear cells co-expressed HAM56. Because of the frequent co-expression of PCNA and HAM56, the main portion of proliferating cells in GCTTS may represent a monocyte/macrophage lineage. However, there is a small but definite mesenchymal/fibroblastic component, characterized by PCNA+vimentin+HAM56-, relating to the proliferative compartment of GCTTS. Multiple immunostainings with MIB-1 showed similar patterns to those with PCNA. These observations indicate that the GCTTS represent bimodal proliferative lesions consisting of histiocytic and mesenchymal/fibroblastic elements.