Patients undergo observation beginning on day 1 of chemotherapy and continuing for up to 3 months in the absence of symptomatic, confirmed deep vein thrombosis or pulmonary embolism; use of anticoagulant therapy for more than 5 days as curative treatment; or initiation of thromboprophylaxis for any reason. Patients undergo bilateral compression ultrasound of the lower limbs at baseline and at 3 months (or at an earlier timepoint, if indicated).