Patients requiring warfarin are not eligible Any patients on warfarin therapy Patients being treated with Warfarin. Requires continued use of warfarin for anticoagulation and cannot stop warfarin to be safely switched to another anticoagulant Patients taking warfarin; if anticoagulation is required, the patient must be on a stable dose of a Food and Drug Administration (FDA) approved anticoagulant other than warfarin (e.g. enoxaparin, dalteparin, fondaparinux, apixaban, rivaroxaban) for at least days Patients must not be receiving systemic anticoagulation with warfarin; patients must be off warfarin for days prior to enrollment; patients who require anticoagulation with an agent other than warfarin will not be excluded, but must be reviewed by the principal investigator prior to enrollment Currently using warfarin. The patient is currently on warfarin or heparin therapy Currently receiving anticoagulation therapy with warfarin; Participants receiving oral warfarin are not eligible for this study (unless warfarin is discontinued at least days prior to commencement of treatment and for the duration of the study, or oral warfarin is converted to LMWH, where local clinical opinion considers this an acceptable option). International normalization ratio (INR) < . times ULN, or if on warfarin, can safely transition off for biopsy International normalization ratio (INR) < . times ULN, or if on warfarin, can safely transition off for biopsy Patients on warfarin Anticoagulation is permitted but patients may not be on warfarin They must not require concomitant treatment with warfarin. International normalized ratio (INR) < ., except for subjects receiving warfarin therapy; for subjects who are receiving warfarin for prophylaxis or treatment of thrombosis, INR values should be carefully monitored while patients are on study Anticoagulation with warfarin Requirement for anticoagulation with warfarin Currently receiving anticoagulation therapy with warfarin; Requires continued use of warfarin for anticoagulation and cannot stop warfarin or be safely switched to another anticoagulant Individuals who require therapy with warfarin Receiving warfarin therapy and cannot tolerate drug substitution Patients receiving chronic or acute warfarin treatment are not excluded, but should be monitored very closely or considered for switch to other therapies. PA- is both highly protein bound and a competitive inhibitor of CYPC at higher concentrations and thus may potentiate the action of warfarin in patients Patients receiving warfarin anticoagulation, who cannot be transitioned to other agents such as enoxaparin or dabigatran, and for whom anticoagulants cannot be held for up to hours Anticoagulation with warfarin Current therapeutic anticoagulation with warfarin (or coumarin derivatives) Requirement for chronic anticoagulation with warfarin or with direct oral anticoagulants at the time of screening. Patients must not be receiving active systemic anticoagulation with heparin or warfarin; patients must be off warfarin therapy for at least days prior to enrollment Patients taking warfarin or platelet inhibitors Treatment with warfarin or other vitamin K antagonist; patients with using warfarin who switch to another form of anticoagulation will be eligible Patients who require warfarin for anticoagulation (other anticoagulants are allowed) Partial thromboplastin time (PTT) =< , international normalized ratio (INR) =< . x institutional ULN unless on warfarin therapy (investigator would need to determine if safe for participant to stop warfarin prior to biopsy and warfarin therapy) Patients on warfarin for any reason Receiving warfarin treatment Patients must not be on phenytoin, warfarin or methadone International normalized ratio (INR) =< . institutional ULN unless on warfarin therapy (investigator would need to determine if safe for participant to stop warfarin prior to biopsy) Current therapeutic anticoagulation with warfarin (or coumarin derivatives) Current treatment with warfarin Receiving warfarin Warfarin is not permitted Therapeutic anticoagulation with warfarin, heparins, or heparinoids Patients receiving warfarin anticoagulation, who cannot be transferred to other agents such as enoxaparin or dabigatran, and for whom anticoagulants cannot be held for up to hours will be excluded Any condition requiring warfarin or thrombolytic anticoagulants PT INR > . unless the patient is on full-dose warfarin Coagulopathies - patients requiring full dose anticoagulation with warfarin are excluded, however, patients stable and on other anticoagulants can be included. Able to take anticoagulation, warfarin or equivalent agent, as detailed in the treatment plan Receiving chronic anticoagulation therapy (e.g. warfarin, heparin) other than aspirin PT INR > . unless the patient is on full-dose warfarin Patients on warfarin or plavix Patients receiving warfarin anticoagulation, who cannot be transferred to other agents such as enoxaparin or dabigatran, and for whom anticoagulants cannot be held for up to hours will be excluded International normalized ratio (INR) =< . ULN unless on warfarin therapy (investigator would need to determine if safe for participant to stop warfarin prior to surgery and warfarin therapy) Warfarin: In-range INR (usually between and ) within days prior to registration Receiving warfarin at registration Anticoagulation with warfarin Are being treated with warfarin anticoagulation therapy Receiving Warfarin Are on an anticoagulant (warfarin, apixaban, dabigatran, and rivaroxaban) regimen Warfarin is not permitted Any condition requiring warfarin or thrombolytic anticoagulants