Background: The expression of HER2, estrogen (ER) and progesterone (PR) receptor can change during the course of the disease in breast cancer (BC). Therefore, reassessment of these markers at the time of disease progression might help to optimize treatment decisions. In this context, characterization of circulating tumor cells (CTCs) could be of relevance since metastatic tissue may be difficult to obtain for repeated analysis. Here we compared HER2/ER/PR expression profiles of primary tumors, metastases and CTCs.
Methods: Ninety-six patients with metastatic BC from seven University BC Centers in Germany were enrolled in this study. Blood was obtained at the time of first diagnosis of metastatic disease or disease progression and analyzed for CTCs using the AdnaTest BreastCancer (QIAGEN Hannover GmbH, Germany) for the expression of EpCAM, MUC-1, HER2, ER and PR. HER2 expression on CTCs was additionally assessed by immunocytochemistry using the CellSearch® assay.
Results: The detection rate for CTCs using the AdnaTest was 43 % (36/84 patients) with the expression rates of 50 % for HER2 (18/36 patients), 19 % for ER (7/36 patients) and 8 % for PR (3/36 patients), respectively. Primary tumors and CTCs displayed a concordant HER2, ER and PR status in 59 % (p = 0.262), 39 % (p = 0.51) and 44 % (p = 0.62) of cases, respectively. For metastases and CTCs, the concordance values were 67 % for HER2 (p = 0.04), 43 % for ER (p = 0.16) and 46 % for PR (p = 0.6). Using the CellSearch® assay, the CTC-positivity rate was 53 % (42/79 patients) with HER2 expressed in 29 % (12/42) of the patients. No significant concordance (58 % and 53 %) was found when HER2 on CTCs was compared with HER2 on primary tumors (p = 0.24) and metastases (p = 0.34). Interestingly, primary tumors and metastases were highly concordant for HER2 (84 %, p = 1.13E-08), ER (90 %, p = 3.26E-10) and PR (83 %, p = 2.09E-09) and ER-and PR-positive metastases were significantly found to be of visceral origin (p = 0.03, p = 0.02).
Conclusion: Here we demonstrate that the molecular detection of HER2 overexpression in CTC is predictive of the HER2 status on metastases. Detailed analysis of ER and PR expression rates in tissue samples and CTCs may provide useful information for making treatment decisions.
Keywords: Biopsy; CTC; Circulating tumor cells; Metastases; Metastatic breast cancer; Receptor expression profile.