Patients with genitourinary cancers (ex: bladder, testicular, kidney) are at high risk of developing blood clots if they receive systemic therapy (ex: chemotherapy, immunotherapy). Blood clots cause pain, may require hospitalization and invasive testing, and in some cases cause death. In fact, blood clots are one of the leading causes of death in patients with cancer. Furthermore, patients who develop a blood clot require medication to thin the blood for a prolonged (sometimes indefinite) period of time, and this can disrupt other important cancer treatments. Studies have shown that using low dose blood thinners to prevent blood clots during systemic therapy is effective in some patients with cancer. However very few patients in these studies had genitourinary cancers, therefore physicians in Canada are not sure if recommending blood thinners to patients with genitourinary cancers is useful or safe. Safety is a primary concern because blood thinners may cause bleeding, and patients with genitourinary cancers may have higher risk of bleeding than patients with other types of cancer. The investigators hypothesize that blood thinners are effective and safe for reducing blood clots in patients with genitourinary cancers. The objective of this study is to determine if a large clinical trial testing the effectiveness and safety of low dose blood thinners for preventing blood clots in patients with genitourinary cancers receiving systemic therapy is feasible.