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.
Society for Cancer Research, Hiscia Institute, Arlesheim, Switzerland. u.weissenstein@vfk.ch
Ulrike
U
Weissenstein
Agnes
A
Schumann
Marcus
M
Reif
Susanne
S
Link
Ulrike D
UD
Toffol-Schmidt
Peter
P
Heusser
D000368:Aged; D000906:Antibodies / Q000276:immunology; D000951:Antigens, Neoplasm / Q000276:immunology / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000378:metabolism; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality / Q000473:pathology; D015815:Cell Adhesion Molecules / Q000276:immunology / Q000378:metabolism*; D045744:Cell Line, Tumor; D000071858:Epithelial Cell Adhesion Molecule; D005260:Female; D006801:Humans; D007633:Keratins / Q000276:immunology / Q000378:metabolism*; D008875:Middle Aged; D009362:Neoplasm Metastasis; D009360:Neoplastic Cells, Circulating / Q000378:metabolism*; D011379:Prognosis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D000906:Antibodies; D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D015815:Cell Adhesion Molecules; D000071858:Epithelial Cell Adhesion Molecule; D007633:Keratins