I have often heard that people diagnosed with deep vein thrombosis (DVT) are evaluated to see if they have an underlying cancer that triggered the clot. Why is that?

This does not happen often, because testing to detect cancer is done only in those patients who show signs that suggest cancer may be present, such as unexplained weight loss or infection. About 10% of people who have DVT/PE will be diagnosed with cancer within 12 months after a DVT or PE. In some cases, with blood clots that do not seem to have any known cause, there may be a need for a more extensive work-up to look for an underlying cancer.