EP300 is a histone acetyltransferase and transcriptional coactivator. Somatic mutations of EP300 have been described in cases of T cell acute lymphoblastic leukemia and other lymphoid malignancies including diffuse large B cell lymphoma and follicular lymphoma. Occasional splice site mutations have also been described which are not detected by this assay. EP300 mutations have also been described in the Rubinstein-Taybi developmental syndrome.