Intracellular accumulation of erlotinib was assessed in the chronic myeloid leukemia cell line, K562, stably transduced with ABCG2 wt, the ABCG2 polymorphisms 34 G > A and 421 C > A, and empty vector. Here, ABCG2 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.