Although many soft tissue tumors can be assigned to recognizable histologic types, a large proportion of tumors do not recapitulate any known mesenchymal lineage. This group includes examples with simple or complex karyotypes; one of each type is described here.
Synovial sarcoma was so-named because the first described cases arose in the soft tissues near the knee joint and a morphologic relationship to synovium was postulated. However, this name is a misnomer, as these tumors can present in locations that lack synovium and their morphologic features are inconsistent with an origin from synoviocytes. Synovial sarcomas account for approximately 10% of all soft tissue sarcomas. Most occur in people in their 20s to 40s. Patients usually present with a deep-seated mass that has been present for several years. Most synovial sarcomas show a characteristic chromosomal translocation t(x;18)(p11;q11) producing fusion genes composed of portions of the SS18 gene and one of three SSX genes that encode chimeric transcription factors that derail cell cycle control.
Fig.21.49Synovialsarcomashowingtheclassicbiphasicspindlecellandglandlikehistologicappearance.
MORPHOLOGYSynovialsarcomasaremicroscopicallymonophasicorbiphasic.Monophasicsynovialsarcomaconsistsofuniformspindlecellswithscantcytoplasmanddensechromatingrowinginshort,tightlypackedfascicles.Thebiphasictypecontainsglandlikestructurescomposedofcuboidaltocolumnarepithelioidcellsinadditiontotheaforementionedspindlecellcomponent(
Fig.
21.49 ).Immunohistochemistryishelpfulinidentifyingthesetumors,sincethetumorcells,especiallyinthebiphasictype,arepositiveforepithelialantigens(e.g.,keratins),differentiatingthemfrommanyothersarcomas.
Synovial sarcomas are treated aggressively with limb-sparing surgery and frequently chemotherapy. The 5-year survival varies from 25% to 62%, related to stage and patient age. Common sites of metastases are the lung and, unusual for sarcomas, regional lymph nodes.
Undifferentiated pleomorphic sarcoma (UPS) includes malignant mesenchymal tumors with high-grade, pleomorphic cells that cannot be classified into another category by a combination of histomorphology, immunophenotype, ultrastructure, and genetics. Most arise in the deep soft tissues of the extremity, especially the thigh of middle-aged or older adults. The diagnosis of malignant fibrous histiocytoma (MFH), sometimes used interchangeably with UPS, has fallen out of use because (1) the category included both undifferentiated tumors and others that could be reclassified with immunohistochemistry and genetics, and (2) no consensus exists for the morphologic definition of fibrohistiocytic lineage. Most tumors are aneuploid with multiple structural and numerical chromosomal changes.
http://ebooksmedicine.net 832CHAPTER 21Bones,Joints,andSoftTissueTumors
Fig.21.50Undifferentiatedpleomorphicsarcomashowinganaplasticspin-dledtopolygonalcells.
MORPHOLOGYUPSsareusuallylarge,grey-whitefleshymassesthatcangrowquitelarge(10–20cm)dependingontheanatomiccompartment.Necrosisandhemorrhagearecommon.Microscopically,theyaresomeofthemostpleomorphicmalignanciesencountered.UPSsconsistofsheetsoflarge,anaplastic,spindledtopolygonalcellswithhyperchromaticirregular,sometimesbizarrenuclei(