Alveolar rhabdomyosarcoma · Alveolus-like pattern -- key low-power feature. Fibrous septae lined by tumour cells. Cells may "fall-off" the septa, i.e. be detached/ ...RhabdomyosarcomaFromLibrePathologyJumptonavigationJumptosearchRhabdomyosarcomaDiagnosisinshortAlveolarrhabdomyosarcoma.H&Estain.LM+/-rhabdomyoblasts(eccentricnucleus,moderateamountofintenslyeosinophiliccytoplasm,striations-notcommon);alveolarRMS:alveolus-likepattern(classic);embryonalRMS:smallroundcelltumourSubtypesembryonal(spindlecellsubtype,botryoid),alveolar(translocation-positive,translocation-negative),undifferentiatedLMDDxsmallroundcelltumours-esp.smallcellcarcinomaand(largecell)lymphomasIHCdesmin(bestmarker)+ve,actin+ve,myogenin+ve,CD56+ve(common),synaptophysin-ve/+ve,chromogranin-ve/+ve,cytokeratins-ve/+veEMsarcomericlikestructures-typicallyinU-shapedcellsMolecularalveolarRMS(~85%ofcases):t(2,13)PAX3/FKHRfusiongeneort(1,13)PAX7/FKHRfusiongeneSitesofttissue-skeletalmusclesite(alveolarRMS),non-skeletalmusclesite(embryonalRMS)ClinicalhistoryalveolarRMS:youngadultoradolescent;embryonalRMS:typically<10yearsoldPrevalencenotcommonClin.DDxothersofttissuetumoursRhabdomyosarcoma,oftenabbreviatedRMS,isamalignanttumourofskeletalmuscle.Contents1General1.1Classification1.1.1Histologic1.1.2Molecularandhistologic2Gross3Microscopic3.1Alveolarrhabdomyosarcoma3.1.1Images3.2Embryonalrhabdomyosarcoma3.2.1SubtypesofembryonalRMS3.3Anaplasia4IHC4.1SubtypingviaIHC5Electronmicroscopy6Moleculardiagnostics6.1Alveolarrhabdomyosarcoma6.2Embryonalrhabdomyosarcoma7Seealso8ReferencesGeneralMostcommonpaediatricsarcoma.Classicallyintheheadandneckregion.[1]MostcommonsarcomainLi-Fraumenisyndrome.[2]~6%ofallchildhoodcancer.ClassificationHistologicAlveolarrhabdomyosarcoma.Usuallyyoungadults/adolescents.Earlymetscommon.Usuallyarisesinregionswithskeletalmuscle.Embryonalrhabdomyosarcoma.Usual<10yearsold.Typicallylocallyinvasive.Usuallyarisesinregionswithoutskeletalmuscle.Lesscommontypes:[3]Undifferentiatedrhabdomyosarcoma.Botryoid-may