This study enrolled patients with measurable metastatic colorectal cancer. Blood was drawn prior to the patient receiving a new therapy for his/her cancer and subsequently at 7-14 days, 3-4 weeks, and when an imaging study was done (~every 6 to 12 weeks). The blood was tested to find circulating tumor cells (CTCs) and to count them. The CTC levels were compared to the imaging study results to see if the CTC number and the imaging result (progression/no progression) were in agreement. Maximum active study participation was 12 months with up to 8 blood draws being taken. All patients are currently being followed for up to 24 months from their off study date for survival. The CTC result will also be used to see if there is a difference in survival and progression-free survival for those patients with and without a certain number of CTCs.

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

Oncology patients from academic institutions and private practices