Is there any form of liquid biopsy that can detect ER and Her 2 expression for metastatic breast cancer?  

Yes. The Circulating Tumor Cell Assay is able to detect ER and HER2 expression. But it has not been validated in prospective studies. I do not recommend using it for this purpose as we just do not know the sensitivity and specificity of such an assay. We have previously written a commentary about on...