Tenosynovial giant cell tumor is the term for a benign neoplasm that develops in the synovial lining of joints, tendon sheaths, and bursae. Clinical variants of tenosynovial giant cell tumor include the diffuse type (previously known as pigmented villonodular synovitis), and the localized type. Whereas the diffuse form tends to involve large joints, the localized type usually occurs as a discrete nodule attached to a tendon sheath, commonly in the hand.
Diffuse and localized types of this tumor both harbor a reciprocal somatic chromosomal translocation, t(1;2) (p13;q37), resulting in fusion of the type VI collagen α-3 promoter to the M-CSF gene. Consequently, the tumor cells overexpress M-CSF, which, through autocrine and paracrine effects, stimulates proliferation of macrophages in a manner similar to giant cell tumor of bone (described previously).
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Fig.21.44Tenosynovialgiantcelltumor,diffusetype.(A)Excisedsynoviumwithfrondsandnodulestypicalofpigmentedvillonodularsynovitis.(B)Sheets ofproliferatingcellsintenosynovialgiantcelltumorbulgingthesynoviallining.
MORPHOLOGYIndiffusetumorsthenormallysmoothjointsynoviumisconvertedintoatangledmatbyred-brownfolds,fingerlikeprojections,andnodules(
Fig.21.44A ).Incontrast,localized(nodular)tumorsarewellcircumscribed.Theneoplasticcells,whichaccountforonlyaminorityofthecellsinthemass,arepolygonal,moderatelysized,andresemblesynoviocytes(
Fig.21.44B ).Bothdiffuseandlocalizedvariantsareheavilyinfiltratedbymacrophagescontaininghemosiderinandfoamylipid,oraremultinucleated.
Diffuse tenosynovial giant cell tumor presents in the knee in 80% of cases. Affected individuals typically complain of pain, locking, and recurrent swelling similar to monoarticular arthritis. Sometimes, a palpable mass is appreciated. The localized variant manifests as a solitary, slow-growing, painless mass that frequently involves the hand. Both types are amenable to surgical excision, but recurrence is more common in the diffuse form. Clinical trials are investigating antagonists of the M-CSF signaling pathway for patients with unresectable disease.
By convention, soft tissue refers to non-epithelial tissue excluding the skeleton, joints, central nervous system, hematopoietic and lymphoid tissues Although nonneoplastic conditions can involve soft tissue, they are seldom confined to this compartment, so the area of soft tissue pathology is restricted to neoplasms.
With the exception of skeletal muscle neoplasms, benign soft tissue tumors outnumber their malignant counterparts, the sarcomas, by 100-fold. In the United States, the incidence of soft tissue sarcomas is approximately 12,000 per year, which is less than 1% of all cancers. Sarcomas, however, cause 2% of all cancer mortality, reflecting their aggressive behavior. Most soft tissue tumors arise in the extremities, especially the thigh. Approximately 15% arise in children but the incidence increases with age.
Most sarcomas are sporadic and have no known predisposing cause. A small minority of soft tissue neoplasms are associated with germline mutations in tumor suppressor genes (neurofibromatosis 1, Gardner syndrome, Li-Fraumeni syndrome, Osler-Weber Rendu syndrome). A few tumors can be linked to known environmental exposures such as radiation, burns, or toxins.