Circulating Tumor Cells versus Imaging—Predicting Overall Survival in Metastatic Breast Cancer

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Abstract
Purpose: The presence of ≥5 circulating tumor cells (CTC) in 7.5 mL blood from patients with measurable metastatic breast cancer before and/or after initiation of therapy is associated with shorter progression-free and overall survival. In this report, we compared the use of CTCs to radiology for prediction of overall survival. Experimental Design: One hundred thirty-eight metastatic breast cancer patients had imaging studies done before and a median of 10 weeks after the initiation of therapy. All scans were centrally reviewed by two independent radiologists using WHO criteria to determine radiologic response. CTC counts were determined ∼4 weeks after initiation of therapy. Specimens were analyzed at one of seven laboratories and reviewed by a central laboratory. Results: Interreader variability for radiologic responses and CTC counts were 15.2% and 0.7%, respectively. The median overall survival of 13 (9%) patients with radiologic nonprogression and ≥5 CTCs was significantly shorter than that of the 83 (60%) patients with radiologic nonprogression and P = 0.0389). The median overall survival of the 20 (14%) patients with radiologic progression and P = 0.0039). Conclusions: Assessment of CTCs is an earlier, more reproducible indication of disease status than current imaging methods. CTCs may be a superior surrogate end point, as they are highly reproducible and correlate better with overall survival than do changes determined by traditional radiology.