A 58-year-old man with recently diagnosed lung adenocarcinoma presents with acute left leg swelling and pain. Compression ultrasound is performed. The structure marked **A** in the diagram shows a distended common femoral vein with echogenic intraluminal material that does not collapse under transducer pressure. Which of the following is the most appropriate immediate management for this patient's condition?

Explanation

## Why Low-molecular-weight heparin (enoxaparin) bridged to warfarin is right The non-compressible distended femoral vein with echogenic thrombus (**A**) confirms proximal DVT. This patient has cancer-associated thrombosis (CAT), which is a major acquired hypercoagulable state. Per CHEST 2021 Guidelines and Rumack Diagnostic Ultrasound, LMWH is the preferred anticoagulant for cancer-associated VTE because it has superior efficacy in this high-risk population and allows bridging to warfarin if needed. LMWH (enoxaparin 1 mg/kg SC BID) is the standard-of-care first-line agent for CAT, particularly when there is concern for compliance or need for flexible dosing in the setting of malignancy. ## Why each distractor is wrong - **Rivaroxaban 15 mg BID then 20 mg daily**: While DOACs are first-line for most non-cancer DVT, they are NOT preferred for cancer-associated thrombosis. Recent trials (CARAVAGGIO, HOKUSAI) have shown LMWH and certain DOACs (apixaban/edoxaban) may be used in CAT, but LMWH remains the gold standard and preferred initial choice for this population. - **Apixaban 10 mg BID then 5 mg BID**: Although apixaban has been studied in CAT (CARAVAGGIO trial), it is not the first-line agent. LMWH is preferred for initial management of cancer-associated DVT due to proven superior outcomes and the ability to bridge to warfarin if needed. - **Unfractionated heparin followed by catheter-directed thrombolysis**: UFH is reserved for unstable patients, perioperative bridging, or severe renal failure. CDT is indicated for iliofemoral DVT with symptoms <14 days and low bleeding risk, but this patient has a common femoral vein DVT (not specifically iliofemoral extension documented) and no mention of phlegmasia cerulea dolens. CDT is not routine for all proximal DVT. **High-Yield:** Cancer-associated thrombosis (CAT) = LMWH first-line; DOACs reserved for selected CAT patients; non-compressibility on US is the gold standard diagnostic sign for DVT. [cite: Rumack Diagnostic Ultrasound 5e Ch 27; CHEST 2021 Guidelines on VTE]