STAT5B and breast cancer: Activation of STAT3, STAT5B or JAK2 due to mutational changes are associated with certain heamatopoietic cancers and solid cancers (gastric cancer, breast cancer, lung cancer and oral cancer), while STAT3 and STAT5B are also considered to be bona fide oncogenes, since constitutively-activated forms induce cell transformation and invasion of cancer cells in mice (74–79).