The lesser impact of deleting INPP4B in mouse prostate versus Mcf10a cells reflects the relative abundance of this protein in these two tissues, and it suggests that different cells and tissues may vary with respect to the relative involvement of PTEN and INPP4B in regulating PI(3,4)P2, a conclusion supported by our analysis of a limited collection of breast and prostate cancer cell lines. This evidence concerns the gene PTEN and prostate carcinoma.