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

Herringbone Fibrosarcoma

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 ).

Fatty Tumors

LIPOMA

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.

Morphology.

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.

LIPOSARCOMA

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.

Morphology.

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: 1119