Prometheus's Onco dX assay platform provides technological breakthrough for immunoassay by obtaining a level of sensitivity down to single tumor cells without compromising specificity. This allows assessment of multiple TKI treatment targets, their activation status, as well as down stream signaling proteins using very tiny amount of tissue that can be obtained by FNA or CTCs.

We planned this study to explore biomarkers predictive of clinical response to cetuximab-based treatment in metastatic colorectal cancer using the Prometheus Platform. We will also elucidate signal transduction pathway attributable to cetuximab resistance, monitor changes in the RTK activation status during cetuximab treatment using circulating tumor cells and analyze correlation between the quantity of circulating tumor cells and treatment response to cetuximab.

Inclusion Criteria:

• Patients with histologically confirmed metastatic colorectal cancer
• Cetuximab-based chemotherapy (monotherapy, combination therapy with cytotoxic chemotherapy such as FOLFOX, XELOX, irinotecan, FOLFIRI, XELIRI, first-line, second-line or third-line are all eligible)
• Age > 18 years.
• ECOG Performance Status of 0-2
• Adequate bone marrow, liver and renal function
• Signed and dated informed consent before the start of specific protocol procedures.
• FNA will be performed in patients with feasible biopsy site; ascites or pleural fluid will be collected in metastatic CRC patients with ascites or pleural effusion

Exclusion Criteria:

• Active clinically serious infections (> grade 2 CTCAE version 3.0)
• Patients with evidence or history of bleeding diathesis
• Radiotherapy during study or within 4 weeks of start of study drug.
• Prior exposure to the study drug.
• Substance abuse, medical, psychological or social conditions that may interfere with the patient's participation in the study or evaluation of the study results

colorectal cancer patients who are treated with cetuximab