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.

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