To understand the role of PMCA4(b) loss during tumor progression, the endogenous PMCA4b was silenced by a PMCA4-specific short hairpin RNA (sh-RNA), or the GFP-tagged PMCA4b and its endocytosis-defective mutant form PMCA4bLA26 were stably over-expressed in MCF-7 cells. This evidence concerns the gene ATP2B4 and neoplasm.