Inclusion Criteria:

- Measurable metastatic carcinoma of the colon or rectum.

- 1st or 2nd line chemotherapy (3rd line acceptable with epidermal growth factor
receptor [EGFR] targeted therapy)

- Chest/abdomen/pelvis scans every 6-12 weeks

- ECOG 0-2

- Hemoglobin (Hgb) > or = 8g/dl within 7 days prior to enrollment

- Age > or = to 18 years of age

Exclusion Criteria:

- Cumulative weekly blood draws exceeding 150mL/week

- Brain metastasis

- Prior history of other carcinoma within the last 5 years, except ductal carcinoma in
situ (DCIS), non-invasive cervical cancer or non-melanoma skin cancer

- Surgery within 14 days of the initial blood draw, excluding surgical placement of a
central venous device