Aspirin vs. heparin: which prevents clots better after cancer bone surgery?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Patients will first be evaluated for inclusion in a master observational study with the following inclusion criteria: 1. Age ≥18 years 2. Prior or planned surgery on the pelvis or lower extremity 3. Fulfills one of the following: a. Cohort A: Metastatic osseous disease, undergoing: i. Endoprosthetic reconstruction ii. Curettage, cement packing, and fixation with nails, plates, and/or screws iii. Intramedullary nail fixation only b. Cohort B: Primary bone sarcoma, undergoing wide resection, amputation, or reconstruction with endoprosthesis, allograft, or allograft-prosthesis composite (APC). c. Cohort C: Primary soft tissue sarcoma ≥5 cm in diameter, undergoing wide resection 4. Anticoagulation therapy was received or is planned. In addition to fulfilling all the inclusion criteria in Part 1 of this study, participants must also not meet any of the below exclusion criteria in order to be eligible for randomization to either aspirin or LMWH. Exclusion Criteria: 1. Documented prior history of VTE. 2. Preoperative use of therapeutic or prophylactic chemical anticoagulation at the time of surgery. 3. Documented allergy/adverse reaction to either of the two study drugs. 4. Presence of inferior vena cava (IVC) filter. 5. Known, diagnosed hypercoagulable state (other than malignancy). 6. Inability to receive chemical anticoagulation. 7. Preoperative use of full-strength aspirin 325 mg daily; patients already taking aspirin 81 mg daily will not be excluded. 8. Inability for the patient him/herself to give informed consent due to delirium, dementia, or any other reason. 9. Pregnancy 10. Fear of needles that prevents administration of LMWH. 11. Inability to administer medications via needles. 12. For patients with metastatic osseous disease, a Khorana score of ≥3. Pregnancy testing, via a urine or blood test, is a routine part of pre-operative laboratory testing in patients scheduled to undergo orthopaedic surgeries. Attending surgeons may also choose to exclude any patient from randomization at their discretion.