We did not observe any changes in methylation of these 4 CpGs during the development of IM-resistance, these findings are in line with those of different cancer entities, such as glioblastoma multiforme [50], breast-cancer [26] or multiple myeloma [51], where no or only partial impact of ABCG2 methylation could be observed. Here, ABCG2 is linked to plasma cell myeloma.