Benign Hematology Service

VTE treatment group: Patients must have a diagnosis of active cancer and documented first venous thromboembolic event (DVT or PE). Patients must not receive therapeutic doses of unfractionated or low molecular weight heparin for more than 48 hours prior to study registration. Patients who need long-term oral anticoagulant therapy are ineligible.

Control group: Patients must have cancer (matched with an enrolled VTE patient) but do not have thrombosis.

VTE patients will receive tinzaparin 175 U/kg/day for at least 6 months with another 6 months at the investigator's discretion (up to one year study treatment). Patients will be followed for 12 months from study registration.

Control group patients (patients with cancer but without blood clots) will not receive study drug but will be monitored for 12 months from on-study registration. Overall health and response to cancer treatment will be monitored.