Diffuse-type giant cell tumour is a soft-tissue neoplasm characterized by proliferation of synovial-like cells. It is also historically known as “pigmented villonodular tenosynovitis (PVNS)". It is recognized that tenosynovial giant-cell tumour and PVNS are related entities and translocations involving the CSF1 have been identified in both (West 2006 PNAS 103(3):690-5).

This case was of a localized mass on the foot, intimate to a tendon, around the 4th/5th metatarsal bone. The lesion was comprised of larger epithelioid cells with abundant cytoplasm, along with the smaller stromal cells and osteoclast-like giant cells. Numerous foamy macrophages can also be appreciated. The hemosiderin in the lesion is highlighted on the iron stain. The Masson trichrome stain shows collagen buildup, without evidence of neoplastic bone formation. Putting the information together, the diagnosis PVNS is fitting.

This slide shows iron colloidal stain. See related content for H&E and trichrome stains.

LMP63381-Soft Tissue, Diffuse-type giant cell tumour is another example of tenosynovitis (see link in related content).

See related content for references:

1) West, RB., et al. 2006 PNAS 103(3):690-5