Hayes DF et al. (2006) 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 12: 4218–4224

Methods currently used to assess clinical benefit of systemic treatment for metastatic breast cancer (MBC), such as physical examinations, radiological studies and serologic testing, are often inaccurate early in the disease course. Inaccurate assessment can lead to prolongation of treatment with an inactive therapy, or premature discontinuation of a potentially useful therapy. A previous study demonstrated that elevated levels of circulating tumor cells (CTCs) before initiation of a new therapy or 3–5 weeks later are associated with rapid disease progression and death in patients with MBC. Additional follow-up data have now been reported.

The study enrolled 177 patients with MBC who were about to start a new systemic therapy. CTC levels were recorded before initiation of therapy (baseline), and 3–5, 6–8, 9–14 and 15–20 weeks after therapy was started. Survival analyses were performed using a threshold elevated CTC level of ≥5 CTCs/7.5 ml blood.

At each blood draw, patients with <5 CTCs/7.5 ml blood showed significantly longer median progression-free survival times than patients with ≥5 CTCs/7.5 ml (≥6.0 months vs ≤3.6 months at each blood draw; P <0.05 for all comparisons). Median overall survival was also significantly longer in patients with CTC counts below the threshold level (≥18.6 months vs ≤10.9 months at each blood draw; P ≤0.001 for all comparisons).

The authors conclude that detection of elevated CTC levels at any point during therapy can be used to predict disease progression and mortality in patients with MBC, and might be useful in determining when an alternative therapy is required.