Quantification of multiple biomarker expression in circulating tumor cells

Investigations of circulating tumor cells (CTCs) in peripheral blood samples of metastatic cancer patients have shown that the numeration of these cells is an independent prognostic factor and can be used to monitor treatment efficacy in breast, colon and prostate cancer1,2,3. While CTC numeration has prognostic value, it does not inform the choice of effective therapy. Prescription of therapy is based on factors including biomarker expression in the primary tumor, which may have been removed years before the onset of metastatic disease. Work on tumor biomarker characterization of CTCs shows promise as prospective guide to treatment. For example, studies have shown that some patients with Her2 negative primary tumors have Her2 positive CTCs in circulation and a poor outcome4. We have developed multiplexed immunofluorescent assays for measurement of protein expression levels of cancer markers in CTCs...Because CTC detection does not depend on the expression level of an enrichment target, the instrument has good detection sensitivity. We are using the assay to measure expression levels of Her2, ER, ERCC1 and EGFR in CTCs of metastatic breast cancer patients and expression levels of ERCC1, RRM1 and EGFR in CTCs of metastatic lung cancer patients. We are studying the distribution of expression levels of these markers as well as their number during the course therapy. We will assess the relationship between expression and outcome. .