CELLSEARCH® Circulating Tumor Cells (CTC) Test

The CellSearch CTC assay uses peripheral whole blood for the detection, enrichment and quantification of CTC of epithelial origin. CTC measurement helps oncologists to determine the prognosis, in predicting cancer progression and to monitor therapy in the management of patients with metastatic breast, prostate and colorectal cancers.

CellSearch CTC assay is the only FDA approved test for CTC counting in patients with metastatic cancers. Each result of a CTC test is verified by both a laboratory technologist and a pathologist to ensure high quality of reporting.

Clinical use:

1. Predict progression free survival (PFS) and overall survival (OS)

2. Monitor response to therapy

CTC testing population:

Patients with metastatic breast, prostate and colorectal cancers at baseline (prior to therapy) and at follow-ups.

Specimen Collection and Shipment:

For CTC enumeration, 20 ml whole blood must be drawn into two proprietary CellSave Tubes (Veridex). Store sample at room temperature. Date and time of draw are required. The specimen should be shipped promptly (no ice, at 15 to 30°C) to make sure the test can be performed within 96 hours of the blood draw. Samples are accepted Monday through Thursday and not on the day preceding a holiday.


Fill the tube until the blood flow stops to ensure the correct ratio of sample to anticoagulant and preservative. Immediately mix by gently inverting the tube eight times. Tube inversion prevents clotting. Inadequate or delayed mixing may result in inaccurate test results. Do not refrigerate samples.

If the patient is on doxorubicin therapy, allow at least 7 days following administration of a dose of doxorubicin before blood draw.


Metastatic breast cancer: <5 CTCs/7.5 mL blood

Metastatic colorectal cancer: <3 CTCs/7.5 mL blood

Metastatic prostate cancer: <5 CTCs/7.5 mL blood

Clinical Information:

CellSearch CTC Assay is intended for the enumeration of CTCs of epithelial origin found in whole blood of patients with metastatic disease. In several multi-center prospective clinical trials, elevated levels of CTCs have been shown to be a strong, independent predictor of shorter PFS and OS in patients with metastatic breast,1-4 prostate,5 or colorectal cancer.6,7 In these studies the patients were separated into 2 groups based on their CTC count. The favorable group represented patients with a baseline circulating tumor cell count <5/7.5mL, (<3 for colorectal cancer) while the unfavorable group represented patients with a baseline count ≥ 5/7.5mL, (≥ 3 colorectal cancer).

Patients in unfavorable groups were predicted to have shorter progression free survival (2.7 vs. 7.0 months, 4.5 vs. 7.9 months, 4.2 vs. 5.8 months for breast, colorectal and prostate metastatic cancers, respectively) and overall survival (10.9 vs. 21.9 months, 9.4 vs. 18.5 months and 11.5 vs. 21.7 months for breast, colorectal and prostate metastatic cancers, respectively) when compared with patients in favorable groups.

Detection of elevated CTCs at any time during therapy is an accurate indicator of rapid disease progression and shorter survivaI. 2,8

The count of CTCs in patients with metastatic breast cancer, may predict treatment response earlier than imaging (3-4 weeks vs. 8-12 weeks after initiation of therapy).3

In patients with metastatic prostate cancer, CTC counts were shown to be earlier predictors of treatment response than the reduction in prostate­ specific antigen (PSA) levels (2-5 weeks vs. 6-8 weeks).8


CellSearch platform is the first standardized, automated and reproducible system for the detection, enrichment and quantification of circulating tumor cells (CTCs) of epithelial origin in peripheral blood. Epithelial cells that express epithelial cell adhesion molecule (EpCAM) and cytokeratins (CK) 8, 18, and 19 are selected for further analysis.

CellSearch Epithelial cell kit (Veridex LLC) contains an anti-EpCAM ferrofluid capture reagent and immunofluorescent reagents. The anti-EpCAM ferrofluid reagent consists of anti EpCAM magnetic beads which target the EpCAM antigen expressed by some types of epithelial tumors. After immunomagnetic capture, the CTCs are labeled with a fluorescent nucleic acid dye 4',6-diamidino-2-phenylindole (DAPI). Fluorescent-labeled monoclonal antibodies specific for leukocytes (anti CD45-Allophycocyanin) and epithelial cells (anti cytokeratins 8, 18, and 19- phycoerythrin) are used to distinguish epithelial cells from leukocytes. The identification and quantification of CTCs is performed by the CellTracks Analyzer II, a semiautomated fluorescent microscope that enables computer generated reconstruction of cellular images. CTCs are defined as nucleated cells (DAPI+) expressing CK 8, 18, and 19 and lacking CD45.

CTC assay is billable (CPT codes) and also it is a reimbursable test by most payors.

Molecular profiling studies (DNA, RNA) including FISH, array based methodologies, and cellular phenotyping (PSA, HER-2/neu or EGFr ) can be performed on the captured CTCs.

CTC assay has been used for research in urinary bladder, biliary duct, hepatocellular, pancreatic and lung cancers, as well as in melanoma.

Contact person: Cristopher Stone, Supervisor, Special Chemistry, at (716) 845-4741 in the Department of Pathology and Laboratory Medicine for further details. 

Selective references:

1. Cristofanilli M, Budd T. Ellis M, et al. Circulating tumor cells, disease progression, and survival in metastatic breast cancer. N Engl J Med. 2004;351(8):781-791

2. Hayes DF, Cristofanilli M, Budd GT et al. Circulating tumor cells at each follow-up time point during therapy of metastatic breast cancer patients predict progression-free and overall survival. Clin Cancer Res. 2006;12(14 Pt 1):4218-4224

3. Budd GT. Cristofanilli M, Ellis MJ, et al Circulating tumor cells versus imaging-predicting overall survival in metastatic breast cancer. Clin Cancer Res. 2006; 12:6403-6409

4. Miller MC, Doyle GV, Terstappen LW. Significance of Circulating Tumor Cells Detected by the CellSearch System in Patients with Metastatic Breast, Colorectal and Prostate Cancer. J Oncol. 2010;2010:617421

5. de Bono JS, Scher HI, Montgomery RB, et al. Circulating tumor cells predict survival benefit from treatment in metastatic castration-resistant prostate cancer. Clin Cancer Res. 2008 Oct 1;14(19):6302-9

6. Cohen SJ, Punt CJ, Iannotti N, et al. Relationship of circulating tumor cells to tumor response, progression-free survival, and overall survival in patients with metastatic colorectal cancer. J Clin Oncol. 2008 Jul 1;26(19):3213-21

7. Cohen SJ, Punt CJ, Iannotti N, et al: Prognostic significance of circulating tumor cells in patients with metastatic colorectal cancer. Ann Oncol 2009;20(7):1223-1229

8. CellSearch™ Circulating Tumor Cell Kit (Epithelial) package insert 2011. Raritan, NJ Veridex LLC