Diffuse-type tenosynovial giant cell tumor (D-TGCT) is a relatively rare mesenchymal tumor. It is a locally aggressive but virtually nonmetastasizing neoplasm and thus regarded as benign. Only a few D-TGCTs with benign histology have been reported to metastasize. We report an extremely rare case of benign D-TGCT in which multiple metastases developed 9 years after surgery for the primary tumor. The present case suggests that conventional D-TGCT has the potential to form distant metastases, albeit exceptionally rarely, and that this probable implantation phenomenon can be managed conservatively.
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