American Society of Clinical Oncology/College Of American Pathologists guideline recommendations for immunohistochemical testing of estrogen and progesterone receptors in breast cancer

ASCO and College of American Pathologists guideline by Hammond, Hayes, Dowsett, Allred and colleagues, developed with Cancer Care Ontario from a systematic review. Up to 20 percent of immunohistochemical oestrogen and progesterone receptor determinations worldwide may be inaccurate, mostly through variation in pre-analytic handling, positivity thresholds and interpretation. The panel recommends that receptor status be determined on all invasive breast cancers and recurrences, proposes a testing algorithm with specified elements to reduce assay variation, and recommends that assays be considered positive if at least 1 percent of tumour nuclei stain in the presence of expected internal and external control reactivity. The absence of endocrine therapy benefit in receptor-negative disease has been confirmed in large overviews of randomised trials.