ASCO and CAP commissioned a systematic review of the literature on hormone receptor testing published since 1990. That review conducted by ASCO and CCO is being published separately (manuscript in preparation) and served as the primary source of the evidence for this guideline. Articles were selected for inclusion in the systematic review if they met the following prospective criteria. Studies comparing IHC in paraffin-embedded female breast cancer sections with another assay and comparative studies whose objectives were to improve or validate the quality of IHC studies that linked test performance to clinical outcome were specifically sought. Systematic reviews, consensus statements, and practice guidelines from 1990 onward were included if they addressed hormone receptor testing in female breast cancer using IHC in paraffin-embedded sections or gene expression signatures for ER and PgR. A cutoff date of 1990 was chosen because this was the time that IHC began to come into common use. Additional details of the literature search strategy are provided in the Systematic Review (manuscript in preparation).