EP300 and neoplasm: However, since the acetylation of STAT3 (K685) is mediated by histone acetyltransferase P300 [91,92] and the mutation of K685 did not affect Y705 phosphorylation [93], we cannot directly link fedratinib to STAT3 acetylation, suggesting that phosphorylation of STAT3 Y705 may have independent roles in tumorigenesis or tumor progression.