e11574 Background: Systemic treatment choices for breast cancer patients with recurrent disease are usually based on the ER/PR/Her2 biomarker status of the primary cancer. Biomarker discordance between the primary and metastatic sites is well recognised and could have important therapeutic implications. A systematic review was conducted to assess the extent of biomarker discordance between the primary cancer and metastasis, and whether is influenced by the site of metastasis. Methods: An electronic search of multiple literature databases implemented by an information scientist was conducted to identify studies reporting outcomes of ER/PR/Her2 receptor stability between primary site and recurrent disease. Seven reviewers independently screened the 5034 abstracts and full text articles, which were identified according to pre-defined selection criteria. The same reviewers performed data collection from all included studies. Studies that were identified reported on receptor conversion between primary sites of breast cancer and various sites of metastasis including lymph node, liver, brain, lung, skin, GI sites and bone marrow. Results: Preliminary results from 385 eligible studies consistently demonstrated discordance between the primary and metastatic sites. When discordance occurred, the general trend was for loss of hormone receptor. ER hormone status was more stable (discordance 10.2-32.5%) than PR (discordance 25.5-40.7%). HER2 was found to have lower rates of discordance (2.6-14.5%). In general, higher ER/PR discordance was found in bone (40-68%) and liver (0-54%) when compared to other sites brain (36%), lung (9-18%), skin (6-22%), GI (15-40%). In the prospective studies, biomarker discordance led to change in patient management in up to 20% of the patient population. Conclusions: Our results demonstrate that biomarker discordance between primary and distant metastases does occur in breast cancer, occurs more frequently with PR, and the extent of discordance is influenced by the site of metastasis. Further research is required to have a better explanation about the pathophysiology of the biomarker status change and its clinical implications.