Circulating tumor cells (CTCs) are prognostic markers in a variety of solid
tumor malignancies. The potential of CTCs to be used as a "liquid biopsy" to monitor a patient's condition and predict
drug response and resistance is currently under investigation. Using a negative depletion, enrichment methodology, CTCs isolated from the peripheral blood of
breast cancer patients with stage IV
breast cancer undergoing
DNA damaging
therapy with
platinum-based
therapy were enriched. The enriched cell
suspensions were stained with an optimized labeling protocol targeting: nuclei, cytokeratins 8, 18, and 19, the surface marker CD45, and the presence of the
protein γ-H2AX. As a direct or indirect result of
platinum therapy, double-strand break of
DNA initiates phosphorylation of the
histone H2AX, at
serine 139; this phosphorylated form is referred to as γ-H2AX. In addition to γ-H2AX staining in specific locations with the cell nuclei, consistent with previous reports and referred to as foci, more general staining in the cell cytoplasm was also observed in some cells suggesting the potential of cell apoptosis. Our study underscores the utility and the complexity of investigating CTCs as predictive markers of response to various
therapies. Additional studies are ongoing to evaluate the diverse γ-H2AX staining patterns we report here which needs to be further correlated with patient outcomes.