ESR1 and breast cancer: In addition to standard of care testing for ER, PgR, and HER2, there are several multimarker tests now available for breast cancer outcome including: MammaPrint® (49) (Agendia, Irvine, CA, USA); a five-antibody IHC panel Mammostrat® (50) (Clarient Diagnostic Services Inc., Aliso Viejo, CA, USA); Oncotype Dx® (51) (Genomic Health, Redwood City, CA, USA); the PAM50-based ProsignaTM assay (52) (NanoString Technologies, Seattle, WA, USA).