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Cancer and Clotting: Two Sides of the Same Coin?
Doctors interested in taking care of cancer patients must complete specialized training after their residency in internal medicine. This subspecialty training is called a fellowship and usually involves training in both hematology (study of blood disorders, including abnormal clotting and bleeding) and oncology (cancer). These two areas are pretty different, leading some to question why they are not split up into two completely different specialty training programs. For those of us who end up taking care of patients with solid tumors, we often question whether all of this hematology training has much value in our day to day practice.
Increasingly, though, links between clotting and cancer are emerging. As I result, I find myself going back to something that I found a lot less interesting during my training than I do now: the clotting cascade.
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Efficient clotting has been essential to our survival: without it, we would risk fatal bleeding with every scrape. Defects in this system lead to the disease hemophilia (Greek for loves to bleed), a disorder characterized by prolonged bleeding after minor trauma. Advances in the treatment of this disease have been a direct result of knowing which clotting factor (denoted by the roman numerals in the figure) is missing and then replacing it.
Do Anticoagulants (Blood Thinners) Improve Survival in Cancer?
Blood clots are a common problem in cancer, including lung cancer, and several studies have shown that this contributes to diminished survival in cancer patients (abstract here):
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Once a blood clot has been detected, most typically a deep vein thrombosis (DVT) that is commonly detected in the leg, or a pulmonary embolus (PE) (clot in the lung), the standard treatment is blood thinners, usually starting with either “unfractionated” heparin, the older form that is given through an ongoing IV and requires frequent checks of the level of blood thinning and adjustment, or “low-molecular weight heparin” (LMWH), which includes just active pieces of the heparin protein, for which there are several brands that are given once or twice daily as a subcutaneous (under the skin) injection and have a more reliable level of blood thinning, so constant monitoring of the level of blood thinning is not required. Patients commonly transition to the oral blood thinner warfarin/coumadin after several days, largely due to the convenience of maintaining a prolonged blood thinning effect with an oral treatment instead of daily injections (and keeping an IV drip of unfractionated heparin going indefinitely, requiring constant checks of the blood, isn’t feasible). LMWH is also very expensive, while coumadin is quite inexpensive.
The American College of Cancer Physicians (ACCP) actually recommends that patients stay on subcutaneous LMWH (an agent known as dalteparin/Fragmin, based on some trial results we’ll review) for 3-6 months for the majority of cancer patients who develop a blood clot (ACCP reference here). While there isn’t an established optimal duration of keeping blood thinners going after a blood clot in a patient, it is generally felt that the underlying cancer continues to put a patient at greater risk for future blood clots, so blood thinners are often recommended to continue as long as a person has active cancer (so if someone has been treated and has no evidence of disease, it’s considered appropriate to discontinue blood thinners (anticoagulation). Continue reading
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