Circulating tumor cells, colon cancer and bevacizumab: the meaning of zero.

It has been recently observed that in metastatic breast cancer patients treated with bevacizumab, circulating tumor cells (CTC) are often undetected [1]. Due to the large use of bevacizumab as first-line treatment for metastatic colorectal cancer (mCRC), we investigated the predictive value of CTC count in patients with mCRC treated with a first-line chemotherapy plus bevacizumab compared with those treated with chemotherapy plus cetuximab. The predictive value of CTC was defined as the effect of change in CTC number after 2–3 months of treatment on response to therapies evaluated by RECIST criteria. CTC count was carried out through CellSearch system (Veriplex Corporation, Warren, NJ). In a group of 27 patients treated with bevacizumab, the median number of baseline CTC was 2.7 (range 0–37). After 6–12 weeks of treatment, CTC count dropped to 0 in 24 patients (89%) and 1 in 3 patients (11%). Surprisingly, 56% of patients with 0 CTC at follow-up evaluation had a progressive disease (PD) (Table 1, A).