ATF1 and histiocytoma, Angiomatoid fibrous: It is possible that EWSR1 acts as a transcription activator Further, EWSR1/ATF1 (the cyclic AMP-dependent transcription factor ATF-1) fusion gene was discovered by RT-PCR in tumor tissue derived from a patient with AFH, and it also discovered a function of constitutive transcriptional activator7,8.