Apixaban or Enoxaparin After Head and Neck Cancer Surgery

Inclusion Criteria: Participants must: * Provide signed and dated informed consent. * Be willing and able to comply with study procedures and follow-up. * Be 18-89 years old (male or female). * Have a negative pregnancy test within 24 hours before surgery (if woman of childbearing potential). * Have biopsy-proven head and neck cancer, or a suspected cancer awaiting tissue diagnosis (can be confirmed by frozen section at surgery). * Be scheduled for major inpatient or outpatient oncologic head and neck surgery (defined as \>45 minutes operative time). * Be an appropriate surgical candidate (adequate performance status). Eligible diagnoses include (not limited to): * Squamous cell carcinoma of oral cavity, hypopharynx, larynx, nasal cavity * Malignancies from major salivary glands * Non-melanoma skin cancers (squamous cell, basal cell, Merkel cell carcinoma) * Unknown primary tumors of head and neck Exclusion Criteria: Participants cannot: * Lack a tissue diagnosis of head and neck cancer during the study period. * Have one of these conditions instead of eligible cancer: Benign disease; Primary thyroid cancer (lower VTE risk); Lymphoma (not primarily surgical); or Melanoma * Fail to undergo definitive head and neck oncologic surgery (e.g., only diagnostic biopsy). * Have surgery limited to tissue diagnosis only (e.g., direct laryngoscopy, excisional lymph node biopsy). * Be unable (patient or caregiver) to administer the study drug. * Have a positive pregnancy test on the day of surgery. * Have a known history of prior DVT or PE (since extended anticoagulation would be indicated). * Have hereditary or acquired bleeding/clotting disorders. * Have severe renal impairment (CrCl \<30 mL/min). * Have conditions that, in the investigator's judgment, make study participation unsafe or confound results.