Page 805 - Robbins Basic Pathology by Vinay Kumar, Abul K. Abbas, Jon C. Aster
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Joint Tumors and Tumor-Like Lesions 791
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Figure 20–23 Tenosynovial giant cell tumor, diffuse type. A, Excised synovium with fronds and nodules typical of the diffuse variant (arrow). B, Sheets
of proliferating cells in tenosynovial giant cell tumor bulging the synovial lining.
Clinical Features and finger tendon sheaths; it is the most common soft
Diffuse TGCT usually mimics a monoarticular arthritis; it tissue tumor of the hand. Cortical erosion of adjacent bone
affects the knee in 80% of cases, followed by the hip and occurs in approximately 15% of cases. Both lesions are ame-
ankle. Patients typically complain of pain, locking, and nable to surgical resection, but also prone to local recur-
recurrent swelling. Tumor progression limits the range of rence. Recognition of the association of TGCT and M-CSF
movement of the joint. Aggressive lesions erode into adja- gene rearrangement and overexpression has inspired trials
cent bones and soft tissues, causing confusion with other of antagonists of M-CSF or its cognate receptor (M-CSFR,
tumors. In contrast, localized TGCT presents as a solitary, a tyrosine kinase); some excellent responses have been
slowly growing, painless mass frequently involving wrist reported.
SOFT TISSUE (telangiectasia). Specific chromosomal abnormalities and
genetic derangements in these syndromes provide impor-
By convention, the term soft tissue describes any nonepithe- tant clues to the genesis of the neoplasms. Like their mes-
lial tissue other than bone, cartilage, central nervous enchymal brethren, the hematopoietic neoplasms, many
system, hematopoietic, and lymphoid tissues. The focus of soft tissue tumors are associated with highly characteristic
this section is on soft tissue tumors, which are classified chromosomal rearrangements, most commonly transloca-
according to the tissue type they recapitulate, including fat, tions that provide insight into pathogenesis and are diag-
fibrous tissue, and neurovascular tissue (Table 20–4). In nostically useful. Indeed, some tumors, such as synovial
some soft tissue neoplasms, however, no corresponding sarcoma, are virtually defined by their associated
normal counterpart is known. Although soft tissue tumors translocations.
are classified based on recognizable lines of differentiation,
current evidence indicates that these tumors arise from Soft tissue tumors can arise in any location, but approxi-
pluripotent mesenchymal stem cells and are not the result mately 40% of sarcomas occur in the lower extremities,
of malignant transformation of mature mesenchymal cells. especially the thigh. While the overall incidence of sarco-
With the exception of skeletal muscle neoplasms (see mas increases with age, 15% arise in children. Certain sar-
further on), benign soft tissue tumors outnumber their comas tend to appear in certain age groups—for example,
malignant counterparts by at least a hundred-fold. In the rhabdomyosarcoma in childhood, synovial sarcoma in
United States, approximately 12,000 soft tissue sarcomas young adulthood, and liposarcoma and pleomorphic fibro-
are diagnosed annually, representing less than 1% of all blastic or undifferentiated sarcomas in later adult life. Soft
invasive malignancies. However, they cause 2% of all tissue sarcomas usually are treated with wide surgical exci-
cancer deaths, reflecting their lethal nature. sion (frequently limb-sparing), with irradiation and sys-
temic therapy reserved for large high-grade tumors.
Most soft tissue tumors arise without antecedent causes;
rarely, radiation exposure, burn injury, or toxin exposure Several features of soft tissue sarcomas influence
is implicated. Kaposi sarcoma (Chapter 9) is associated prognosis:
with the human herpesvirus 8, but viruses probably are • Diagnostic classification. This is based not only on his
not important in the pathogenesis of most sarcomas in
humans. A small minority of soft tissue tumors are associ- tology, but also on immunohistochemistry, electron
ated with genetic syndromes, most notably neurofibroma- microscopy, cytogenetics, and molecular genetics, which
tosis type 1 (neurofibroma, malignant schwannoma), are indispensable in assigning the correct diagnosis in
Gardner syndrome (fibromatosis), Li-Fraumeni syndrome some cases.
(soft tissue sarcoma), and Osler-Weber-Rendu syndrome
