Background and Aims:Immunohistochemistry (IHC) has replaced radioligand binding assay for the determination of oestrogen receptor (ER) status in breast carcinoma. IHC is also used for assessment of progesterone receptor (PR) and HER2. The Royal College of Pathologists of Australasia (RCPA) Quality Assurance Program (QAP) introduced a breast markers module in 2003 to evaluate the performance of laboratories with IHC for ER, PR and HER2.Methods:An audit of laboratories reporting breast carcinomas was performed in 2005 and 2006 to evaluate in-house results. Laboratories were asked to submit the hormone receptor and HER2 status on each invasive breast carcinoma for the previous 6 month period up to a maximum of 100 cases. The time periods were 1 July 2004 to 31 December 2004, and 1 July 2005 to 31 December 2005. A total of 55 laboratories returned information for 2004 and 67 for 2005.Results:Complete data on 8128 patients was returned for both surveys, 3353 cases for 2004 and 4775 for 2005. The results were similar for both surveys. Of the 8128 cases, 59.0% were ER+/PR+, 15.9% ER+/PR−, 2.4% ER−/PR+ and 22.7% ER−/PR−. HER2 data were submitted for a total of 6512 patients (excludes 52 patients with incomplete data sets); 17.1% were reported as 3+ positive on IHC, 12.5% as 2+ and 70.4% as negative.Conclusions:A laboratory audit was introduced into the RCPA QAP for breast markers due to concerns raised by participating laboratories about technical differences in supplied tissues for testing. This audit indicates that overall the results for ER, PR and HER2 fall inside established parameters. However, a number of individual laboratories do not meet the target values and variation in results would impact on patient treatment decisions.