Thromboembolism a common, costly, and morbid complication that is also associated with decreased survival in cancer patients. The risk of thromboembolism in cancer patients is underappreciated. In addition to symptomatic deep venous thrombosis and pulmonary embolism, asymptomatic and arterial thromboembolic events are important consideration in ambulatory cancer patients receiving neoadjuvant chemoradiotherapy (nCRT). No specific randomized trial examining thromboprophylaxis (TP) during nCRT for gastrointestinal cancer has been performed, and none is accruing. Most guidelines currently recommend against TP in ambulatory cancer patients due to a lack of data rather than proof of harm or lack of efficacy. It is clear that robust data are urgently required, and that treatment with nCRT in patients with gastrointestinal malignancy is not an indication for routine pharmacological TP at the present time.