Analysis of a published proteomic dataset of 60 human tumor cell lines (http://proteomics.wzw.tum.de/nci60) confirmed high levels of INPP4B protein in ER+ breast cancer cell lines (MCF-7 and T47D), and no INPP4B protein was found in ER− breast cancer cell lines (MDA-MB-231, MDA-MB-468, BT549, and HS 578T), supporting the link between INPP4B and ER status. This evidence concerns the gene ESR1 and breast cancer.