Tumor Cytogenetic Abnormality Genetic Abnormality
Extraosseous Ewing sarcoma and primitive neuroectodermal tumor t(11:22)(q24;q12) FLI-1-EWS fusion gene
t(21:22)(q22;q12) ERG-EWS fusion gene
t(7;22)(q22;q12) ETV1-EWS fusion gene
Liposarcoma—myxoid and round cell type t(12:16)(q13;p11) CHOP/TLS fusion gene
Synovial sarcoma t(x;18)(p11;q11) SYT-SSX fusion gene
Rhabdomyosarcoma—alveolar type t(2;13)(q35;q14) PAX3-FKHR fusion gene
t(1;13)(p36;q14) PAX7-FKHR fusion gene
Extraskeletal myxoid chondrosarcoma t(9;22)(q22;q12) CHN-EWS fusion gene
Desmoplastic small round cell tumor t(11;22)(p13;q12) EWS-WT1 fusion gene
Clear cell sarcoma t(12;22)(q13;q12) EWS-ATF1 fusion gene
Dermatofibrosarcoma protuberans t(17:22)(q22;q15) COLA1-PDGFB fusion gene
Alveolar soft part sarcoma t(X;17)(p11.2;q25) TFE3-ASPL fusion gene
Congenital fibrosarcoma t(12;15)(p13;q23) ETV6-NTRK3 fusion gene
TABLE 26-10-- Morphology of Cells in Soft Tissue Tumors
Cell Type Features Tumor Type
Spindle cell Rod-shaped, long axis twice as great as short axis Fibrous, fibrohistiocytic, smooth muscle, Schwann cell
Small round cell Size of a lymphocyte with little cytoplasm Rhabdomyosarcoma, primitive neuroectodermal tumor
Epithelioid Polyhedral with abundant cytoplasm, nucleus is centrally located Smooth muscle, Schwann cell endothelial, epithelioid sarcoma
TABLE 26-11-- Architectural Patterns in Soft Tissue Tumors
Pattern Tumor Type
Fascicles of eosinophilic spindle cells intersecting at right angles Smooth muscle
Short fascicles of spindle cells radiating from a central point (like spokes on a wheel)—storiform Fibrohistiocytic
Nuclei arranged in columns—palisading Schwann cell
Mixture of fascicles of spindle cells and groups of epithelioid cells—biphasic Synovial sarcoma
With this brief background, we now turn to the individual tumors and tumor-like lesions. Some of the soft tissue tumors are presented elsewhere—tumors of peripheral nerve ( Chapter
27 ); and tumors of vascular origin, including Kaposi sarcoma ( Chapter 11 ).
Benign tumors of fat, known as lipomas, are the most common soft tissue tumor of adulthood. They are subclassified according to particular morphologic features as conventional
lipoma, fibrolipoma, angiolipoma, spindle cell lipoma, myelolipoma, and pleomorphic lipoma. Some of the variants have characteristic chromosomal abnormalities; for example,
conventional lipomas often show rearrangements of 12q14-15, 6p, and 13q, and spindle cell and pleomorphic lipomas have rearrangements of 16q and 13q.
The conventional lipoma, the most common subtype, is a well-encapsulated mass of mature adipocytes that varies considerably in size. It arises in the subcutis of the proximal
extremities and trunk, most frequently during mid-adulthood. Infrequently, lipomas are large, intramuscular, and poorly circumscribed. Histologically, they consist of mature white fat
cells with no pleomorphism.
Lipomas are soft, mobile, and painless (except angiolipoma) and are usually cured by simple excision.
Liposarcomas are one of the most common sarcomas of adulthood and appear in those in their forties to sixties; they are uncommon in children. They usually arise in the deep soft
tissues of the proximal extremities and retroperitoneum and are notorious for developing into large tumors.
Histologically, liposarcomas can be divided into well-differentiated, myxoid, round cell, and pleomorphic variants. The cells in well-differentiated liposarcomas are readily recognized as
lipocytes. In the other variants, most of the tumor cells are not obviously adipogenic, but some cells indicative of fatty differentiation are almost always present. These cells are known as
lipoblasts;they mimic fetal fat cells and contain round clear cytoplasmic vacuoles of lipid that scallop the nucleus ( Fig. 26-53 ). The myxoid and round cell variant of liposarcoma has a
t(12;16) chromosomal abnormality in most cases ( Table 26-9 ).
The well-differentiated variant is relatively indolent, the myxoid type is intermediate in its malignant behavior, and the round cell and pleomorphic variants usually are aggressive and
frequently metastasize. All types of liposarcoma recur locally and often repeatedly unless adequately excised.
Date: 2016-04-22; view: 278