To investigate the clinicopathologic features and immunophenotype of localized-type giant cell tumor of the tendon sheath (L-GCTS).

A clinicopathologic analysis of 54 cases of L-GCTS was performed. Among them, immunohistochemical staining was performed on 16 cases. The related literature was also reviewed.

The male-to-female ratio of L-GCTS patients was 1:1.7, and the mean age was 36.7 (8-62) years old. L-GCTS was often located on the right thumb, with an average diameter of 1.6 cm, and many had complete capsules. The tumor was mainly composed of large synovial mononuclear cells, small histologic cell-like monocytes, fibroblasts, and osteoclast-like multinucleated giant cells. According to the histological features, it was divided into three histological types: proliferative, fibrous histiocytoma-like, and fibrotic. Immunohistochemical staining showed that clusterin was strongly positively expressed only in large synovial-like mononuclear cells, and CD163 showed strongly positive expression in the small histiocytoid cells. Both CD68 and vimentin were expressed in all four types of cells, but the expression varied. Ki-67 positive cells were monocytes, and the proliferation index was 3%~12% (average, 5%).

L-GCTS are tumors that differentiate towards the synovial epithelium, and can be divided into three subtypes according to their tissue morphology, reflecting the morphological characteristics of different time periods. There is often overlap between the types. Complete local resection of the tumor is the most important treatment. In order to prevent recurrence, local radiotherapy or targeted therapy can be used as an adjuvant therapy.