Given that NHE1 over-expression partially rescued the effects of digitoxin plus MEK inhibitor on intracellular acidification (Fig. 4g), mitochondrial Ca2+ levels (Fig. 5j,k) and cell death (Fig. 4h), our results raised the question of whether NHE1 over-expression could rescue the effects of digitoxin plus MEK inhibitor on tumour growth. This evidence concerns the gene MAP2K7 and neoplasm.