Chondroid tenosynovial giant cell tumor: a clinicopathological and immunohistochemical analysis of 5 new cases.

Tenosynovial giant cell tumor (TGCT) arises from the synovium of joints or tendon sheaths. Chondroid metaplasia in TGCT is rare with only 4 well-documented cases reported in the literature. The authors describe the morphological features and immunophenotype of 5 new cases of chondroid TGCT emphasizing a broader range of matrix patterns in these tumors and an expanded immunophenotype, specifically, staining for clusterin and podoplanin which have recently been found to be expressed in conventional TGCTs. Chondroid metaplasia was extensive in 3 cases. Matrix patterns included chondromyxoid, chondro-osseous, hyaline-like, and lace-like calcification similar to that seen in chondroblastoma. The authors conclude that chondroid TGCT is a rare, distinct synovial tumor with a predilection for the temporomandibular joint that has a similar immunophenotype as conventional TGCT. Chondroid metaplasia may be extensive and have a variety of matrix patterns. Chondroid TGCT needs to be distinguished from other chondroid lesions, including chondroblastoma and chondrosarcoma.