biostudies-literatureStacchiotti SNCI NIH HHS2934-2942https://www.ebi.ac.uk/biostudies/studies/S-EPMC8319065biostudies-literatureUnknown127(16)<h4>Background</h4>Among sarcomas, which are rare cancers, many types are exceedingly rare; however, a definition of ultra-rare cancers has not been established. The problem of ultra-rare sarcomas is particularly relevant because they represent unique diseases, and their rarity poses major challenges for diagnosis, understanding disease biology, generating clinical evidence to support new drug development, and achieving formal authorization for novel therapies.<h4>Methods</h4>The Connective Tissue Oncology Society promoted a consensus effort in November 2019 to establish how to define ultra-rare sarcomas through expert consensus and epidemiologic data and to work out a comprehensive list of these diseases. The list of ultra-rare sarcomas was based on the 2020 World Health Organization clasCancerUltra-rare sarcomas: A consensus paper from the Connective Tissue Oncology Society community of experts on the incidence threshold and the list of entities.PMC8319065P30 CA008748K08 CA241085Baldini EHJones RLDei Tos APStacchiotti SMatsuda TFletcher CDMHayes-Jardon ADemetri GDMir OSanfilippo RGBonvalot SGupta AMaestro RPatel SRSundby Hall KFrezza AMMartin Broto JTrama AKasper BChiang RCGronchi AKleinerman ESBlay JYGounder MMEriksson MHaas RLKawai ASchaefer IMvan der Graaf WTAWon YJDesai JGelderblom HHohenberger PThomas DMChirlaque Lopez MDMarcos-Gragera RCallegaro DLe Cesne AGeorge SVisser OStrauss DCCasali PGRutkowski PJones KBvon Mehren MWagner AJBovee JVMGReed DRRazak ARATap WDWilky BAKirsch DGSbaraglia MRaut CPDemicco EGLim Jvan Houdt WJfalseUltra-rare sarcomas: A consensus paper from the Connective Tissue Oncology Society community of experts on the incidence threshold and the list of entities.<h4>Background</h4>Among sarcomas, which are rare cancers, many types are exceedingly rare; however, a definition of ultra-rare cancers has not been established. The problem of ultra-rare sarcomas is particularly relevant because they represent unique diseases, and their rarity poses major challenges for diagnosis, understanding disease biology, generating clinical evidence to support new drug development, and achieving formal authorization for novel therapies.<h4>Methods</h4>The Connective Tissue Oncology Society promoted a consensus effort in November 2019 to establish how to define ultra-rare sarcomas through expert consensus and epidemiologic data and to work out a comprehensive list of these diseases. The list of ultra-rare sarcomas was based on the 2020 World Health Organization clas2021-01-01T00:00:00Z2021 Aug2026-05-09T11:46:57.916Z2022-02-11T07:18:39.903ZS-EPMC83190653391026310.1002/cncr.33618