Immunocytochemistry staining for ER and PR in circulating tumor cells as compared to primary tumor or metastatic biopsy.

584 Background: Hormone receptor (estrogen receptor [ER] and progesterone receptor [PR]) status in all breast cancer patients is recommended for selection of treatment options. However, the analytical sensitivity of immunohistochemistry (IHC) in detecting low levels of ER/PR is often poor and is likely due to methodological variation. Because biopsy is not often feasible in all patients with recurrent and/or metastatic breast disease, circulating tumor cells (CTCs) offer an attractive alternative source of tumor tissue for determining ER/PR status and can be monitored more readily to enable a more effective course of treatment. Methods: Twenty mL of peripheral blood was collected prospectively from 15 patients diagnosed with late stage metastatic/recurrent breast cancer. CTCs were isolated using the microfluidic OncoCEE platform. A cocktail of antibodies was utilized for CTC capture and detection with an expanded anti-cytokeratin (CK) cocktail mixture and anti-CD45. ER/PR protein expression was assessed b...