STAT5B and chronic myelogenous leukemia, BCR-ABL1 positive: Moreover, our finding also provides an explanation for the observation that constitutive STAT5 activation coincides with functional loss of p53 in B-cell lymphoma/leukemia.30 It was also demonstrated that knockdown of STAT5A in CML hematopoietic progenitors could dramatically increase the p53 expression level,29 which is in line with our data.