 Since this protocol includes blood draws at multiple time points at different distances from the metastases, results could further clarify if the rarity or absence of CTCs in the peripheral blood of some mCRC patients can be explained by dilution. Comparison of patients with CRC liver to lung metastases might help explain different patterns of organ spread. Results of this study could establish CTCs as a prognostic biomarker identifying candidates who will benefit from metastasectomy or for those who are candidates for additional or palliative systemic treatments because of a high risk for later recurrence. 