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.

We evaluated 193 blood samples from metastatic breast cancer patients at the time of first diagnosis of metastatic disease or disease progression. All samples underwent immunomagnetic enrichment using the AdnaTest BreastCancerSelect (AdnaGen AG, Germany) within 4h after blood withdrawal followed by RNA isolation and subsequent gene expression analysis by reverse transcription and Multiplex-PCR in separated tumor cells using the AdnaTest BreastCancerDetect. CTCs were analyzed for the three breast cancer-associated markers: EpCAM, Muc-1, Her-2 and actin as an internal PCR control. Expression of the ER and PR was assessed in an additional RT-PCR. The analysis of PCR products was performed by capillary electrophoresis on the Agilent Bioanalyzer 2100.

The overall detection rate for CTCs was 45% (87/193 patients) with the expression rates of 71% for EpCAM (62/87 patients), 73% for MUC1 (64/87 patients), 48% for HER2 (42/87 patients), 19% for ER (17/87 patients) and 10% for PR (9/87 patients), respectively. Comparisons with the primary tumor were only performed in CTC+ patients (n=87). In 48/62 (77%) patients with ER+ tumors, CTCs were ER− and 46/53 (87%) patients with PR+ tumors did not express PR on CTCs. Primary tumors and CTCs displayed a concordant ER and PR status in only 41% (p=0.260) and 45% (p=0.274) of cases, respectively.

Most of the CTCs were ER/PR-negative despite the presence of an ER/PR- positive primary tumor. The predictive value of hormone receptor status expression profile of CTCs for palliative endocrine therapy has to be prospectively evaluated.

We recently demonstrated in more than 400 primary breast cancer patients that the expression profile between CTCs and the primary tumor with regard to ER/PR/HER2 positivity differs. The concordance rate between ER, PR and HER2 status of CTCs and the primary tumor was 29%, 25% and 53%, respectively (Fehm T et al., Breast Cancer Res Aug 10 2009, 11(4) pR59). Based on these results we studied blood samples of 193 metastatic breast cancer patients participating in the German DETECT 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. As already shown for primary breast cancer, most of the CTCs were ER/PR-negative despite the presence of an ER/PR- positive primary tumor. In the metastatic setting the phenotype of CTC reflects the phenotype of metastatic disease. Therefore palliative treatment selected based on the expression profile may not be effective since the phenotype has changed during disease progression. To our knowledge, this study is one of the biggest to compare hormonal receptor expression on CTC and the primary tumor. We hope that our manuscript is suitable for publication in Gynecologic Oncology.