Breast cancer can be positive for expression of a hormone receptor (ESR/PGR/AR) or a growth factor receptor (ERBB2). Disease recurrence following disease remission (relapse), resistance to endocrine therapy or otherwise inadequate long-term control of disease are challenges that limit effectiveness of existing drugs that treat luminal A and luminal B disease. Here we utilized whole transcriptome technologies (5, 6) to measure total transcription in the primary tumors of humans with luminal A and luminal B breast cancer. We describe one member of a group of phosphatases up-regulated and differentially expressed in human luminal B breast cancer, PGP, as a catalytically available phosphatase and candidate therapeutic target for the adjunctive medical treatment of luminal B breast cancer.