Although in the last few years there has been a greater focus on low molecular weight heparins (LMWHs), which are injected, the oral anticoagulant (blood thinner) has been studied in this capacity and is certainly widely used in clinical practice for patients with blood clots due to its oral administration, which is desirable particularly if treatment may be indefinite. This agent interferes with several proteins involved with the body’s normal mechanism for blood clotting, which is good if you need to heal a wound, but it’s a delicate balance that is harmful if people develop clots more often than they’re needed, which is often the case with cancer. We know that cancer patients who develop a blood clot are at a higher risk of a recurrent blood clot than other people who don’t have cancer but have a blood clot.

Although heparin has been more extensively studied in this setting, there is some limited evidence that coumadin may have some direct inhibitory effects on tumor growth and metastatic spread (abstract here). Typically, the results in actual people are more complicated. In 1984, a large trial with 431 patients from the VA system with a wide range of cancer types (lung, head and neck, colon, and prostate cancer) were randomized to receive chemotherapy with either life-long coumadin or a placebo (abstract here). There were no significant differences in overall survival for the general cancer population, but among the 50 patients with SCLC, median survival was doubled (50 vs. 24 weeks, p = 0.03). Here are the survival curves for coumadin vs. placebo with NSCLC and SCLC:

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