Alternatively, TET1 expression in immortalized human bronchial epithelial cells is reduced subsequent to activation of the RAS/RAF/MEK/ERK signal transduction pathway, via transfection of the cells with a constitutively active RAS oncogene [157], but unlike the breast cancer cells above, no effect on HMGA2 or HOXA9 expression was detected. Here, HMGA2 is linked to breast cancer.