How much variability can you see in levels of ER/PR expression between the primary tumor and a metastasis to make you reconsider if it's a second primary?

Expression of estrogen, progesterone receptors can vary over time and between primary and metastatic sites in approximately 10-15% of cases based on literature. It can also be affected by technical aspects such as cold ischemia time, negative/positive controls used and pathologist interpretation of the IHC staining. Testing for ER, PR and HER2 on decalcified bone biopsy is even less reliable. In addition, the management of a patient with metastatic breast cancer would still be palliative and would mainly involve systemic therapy rather than definitive surgery whether or not there was a secondary breast cancer with similar receptor status. The only exception is that new disease would have to be accounted in the decision on whether to change ...