ATF1 and clear cell sarcoma: <b>Background:</b> Clear cell sarcoma (CCS) is an ultrarare sarcoma driven by a specific chromosomal translocation, most commonly the EWS RNA binding protein 1-activating transcription factor 1 fusion (<i>EWSR1::ATF1</i>), for which chemotherapy shows limited activity, with a median progression-free survival (PFS) of approximately 3 months in retrospective series.