Detection of circulating tumor cells in blood of metastatic breast cancer patients using a combination of cytokeratin and EpCAM antibodies

BACKGROUND

Circulating tumor cells (CTCs) are detectable in peripheral blood of metastatic breast cancer patients (MBC). In this paper we evaluate a new CTC separation method based on a combination of anti-EpCAM- and anti-cytokeratin magnetic cell separation with the aim to improve CTC detection with low target antigen densities.

METHODS

Blood samples of healthy donors spiked with breast cancer cell line HCC1937 were used to determine accuracy and precision of the method. 10 healthy subjects were examined to evaluate specificity. CTC counts in 59 patients with MBC were measured to evaluate the prognostic value on overall survival.

RESULTS

Regression analysis of numbers of recovered vs. spiked HCC1937 cells yielded a coefficient of determination of R(2) = 0.957. The average percentage of cell recovery was 84%. The average within-run coefficient of variation for spiking of 185, 85 and 30 cells was 14%. For spiking of 10 cells the within-run CV was 30%. No CTCs were detected in blood of 10 healthy subjects examined. A standard threshold of 5 CTC/7.5 ml blood as a cut-off point between risk groups led to a highly significant prognostic marker (p < 0.001). To assess the prognostic value of medium CTC levels we additionally considered a low (CTC-L: 0 CTC), a medium (CTC-M: 1-4 CTC) and a high risk group (CTC-H: ≥5 CTC). The effect of this CTC-LMH marker on overall survival was significant as well (p < 0.001). A log-ratio test performed to compare the model with 3 vs. the model with 2 risk groups rejected the model with 2 risk groups (p = 0.026). For CTC as a count variable, we propose an offset reciprocal transformation 1/(1 + x) for overall survival prediction (p < 0.001).

CONCLUSIONS

We show that our CTC detection method is feasible and leads to accurate and reliable results. Our data suggest that a refined differentiation between patients with different CTC levels is reasonable.

Let me do more than count the ways: what circulating tumor cells can tell us about the biology of cancer

Tumor cells in the circulation of patients with advanced cancers have been described for over a century, but only recently have methods become available to reproducibly and robustly detect these cells in patients with cancer. A variety of methods have been developed to study this phenomenon, reflecting a broad interest in the field. The presence of circulating tumor cells (CTCs) in the peripheral blood of patients with metastatic cancer has been found to be of prognostic significance, and changes in CTC numbers over time appear to reflect treatment outcome. The ability to detect and study CTCs suggests that CTC concentration in blood may be able to be used as an intermediate biomarker in therapeutic trials of novel therapies in cancer patients and that molecular changes in patients' tumors may be able to be detected and addressed with appropriate therapeutic interventions. Studies in patients with early, nonmetastatic cancers are beginning, and some studies indicate that circulating tumor cells can predict outcome in this setting. While the ability to count and characterize circulating tumor cells holds much potential for the future, improvements in and standardization of assay methods need to be made before the potential of this technology is fully realized.