Permission to Collect Blood Over Time for Research

Inclusion Criteria:

Male or female, >= 18 years old. There are no ethnic restrictions.
Active cancers of the GI tract (gastroesophageal, colorectal, or pancreatic-biliary) that have completed TNM staging by the American Joint Committee on Cancer; stage III disease if diagnosed within 2 months and all stage IV disease
Ability to understand and the willingness to sign a written informed consent document.
Existing staging CT imaging study

Exclusion Criteria:

Life expectancy < 6 months
History of deep vein thrombosis (DVT) or pulmonary embolism (PE)
Known pregnancy or positive urine pregnancy test in pre-menopausal women
On anticoagulant therapy (heparin, warfarin, direct thrombin inhibitors)
No CT imaging studies, or contraindications to undergoing CT imaging
Existing or anticipated need for a tunneled central venous catheter
Clinic visitation to Stanford Cancer center for secondary consultation purposes only
Inability to give informed consent