Rivaroxaban or Aspirin As Thromboprophylaxis in Multiple Myeloma

Inclusion Criteria: 1. Diagnosis of Multiple Myeloma 2. Scheduled to start on Len-Dex therapy 3. Be ≥ 18 years of age 4. Able to provide written informed consent 5. Pre-clinical laboratory must meet the following criteria at enrollment * Platelet count \>50 × 109/L * Creatinine clearance (CrCl) \>15mL/min using Cockcroft-Gault Equation Exclusion Criteria: 1. Major bleeding event within the previous 3 months prior to commencement of Len Dex therapy 2. Documented severe liver disease in the past 6 months (eg. acute clinical hepatitis, chronic active hepatitis, or cirrhosis) 3. Patient with a history of antiphospholipid syndrome especially if he/she is triple positive for lupus anticoagulant, anticardiolipin antibodies, and/or anti-b2 glycoprotein I antibodies. 4. A history of malignancy (with the exception of MM) within 2 years before randomization or any previously diagnosed malignancy with evidence of residual disease. Patients with a history of basal cell or squamous carcinoma are not excluded. 5. Patient with history of gastric or duodenal ulcer within 2 years 6. Plasma cell leukemia; systemic amyloidosis 7. Patient on therapeutic anticoagulation for treatment of VTE or ATE, or stroke prevention in non-valvular atrial fibrillation. Patients with a previous history of VTE who are not on any active anticoagulant therapy will not be excluded. 8. Patient on antiplatelet agents due to an absolute indication (e.g.; coronary stent, carotid stent). 9. Patients receiving concomitant systemic treatment with strong inhibitors of both CYP3A4 and P-gp such as ketoconazole, itraconazole, posaconazole or ritonavir) 10. Patient on single agent lenalidomide 11. Life expectancy less than 3 months as determined by the investigator. 12. Unstable medical or psychological condition that would interfere with trial participation, as determined by the investigator 13. Patient not able or not willing to give consent to participate in the study 14. Uncontrolled cardiovascular disease within 6 months prior to enrollment 15. Uncontrolled or poorly controlled diabetes or renal disease 16. Major surgery within 2 weeks before randomization 17. Known allergies, hypersensitivity, or intolerance to any of the study drugs. 18. Patients not able or not willing to give consent to participate in the Study.