The expression of predictive markers including the estrogen (ER) and progesterone receptor (PR) expression can change during the course of the disease. Therefore, reassessment of these markers at the time of disease progression might help to optimize treatment decisions. Metastatic tissue may be difficult to obtain for repeated analysis. In this context, characterization of circulating tumor cells (CTCs) could be of relevance. It was the purpose of the present study (1) to reevaluate the ER/PR expression by CTCs and (2) to compare the hormone receptor status expression profile of CTCs with the primary tumor.
