**Core Concept**
Venous thromboembolism (VTE) prophylaxis in cancer patients undergoing surgery requires anticoagulation that is effective, safe, and rapidly reversible. Cancer-associated hypercoagulability increases VTE risk, and prophylactic anticoagulants must be administered early and with minimal bleeding risk.

**Why the Correct Answer is Right**
Low molecular weight heparin (LMWH) is the anticoagulant of choice for VTE prophylaxis in cancer patients post-surgery. It has a more predictable pharmacokinetic profile than unfractionated heparin, requires no routine monitoring, and has a lower risk of bleeding compared to warfarin. LMWH is effective in both preventing thrombosis and treating early VTE, and it is well-tolerated in patients with malignancy. Its action is mediated through inhibition of factor Xa and thrombin, with a longer half-life than unfractionated heparin, allowing for once-daily dosing.

**Why Each Wrong Option is Incorrect**
Option A: Heparin sulfate is not a clinically used anticoagulant; it is a naturally occurring glycosaminoglycan with no therapeutic anticoagulant activity.
Option B: Protamine sulfate is a reversal agent for heparin, not a prophylactic anticoagulant. It is used in emergencies to reverse heparin effects, not for routine VTE prevention.
Option D: Warfarin has a long onset of action, requires frequent monitoring, and carries a higher risk of bleeding and drug interactions in cancer patients, especially with chemotherapy. It is not recommended for initial prophylaxis.

**Clinical Pearl / High-Yield Fact**
In cancer patients, LMWH is preferred over warfarin for VTE prophylaxis due to its rapid onset, predictable dosing, and lower bleeding risk—making it safer in a population with high thrombotic risk and coagulopathy.

✓ Correct Answer: C. Low molecular weight heparin