The link between tumors and blood clots was described in 1865 by the French physician Armand Trousseau, but he could not provide a scientific explanation. In more recent times, the relationship has become clearer and we now know that the link works in two ways: on one hand, patients with cancer have an increased risk of thrombosis and, on the other hand, tumor growth and metastasis can be facilitated by the activation of coagulation and the mechanisms leading to thrombosis.

Recent studies have shown that cancer patients have 4–6-times the risk of thrombosis compared to the general population, and an episode of thrombosis in these patients has a negative impact on their survival. The risk is highest in the first few months after a cancer diagnosis, but persists for many years. It rises further during chemotherapy.

The incidence of thrombosis in cancer patients varies with the type and stage of the tumor. It is highest in patients with tumors of the pancreas, stomach, brain, kidneys, uterus, lungs and ovaries, especially if the disease is advanced. Breast cancer has a lower risk of thrombosis compared with other tumors, especially in its early stages. Among hematological tumors, the incidence is highest for lymphoma and myeloma.

The pathogenesis of thrombosis in cancer is complex and multifaceted. There are general factors, factors linked to the body’s inflammatory response to the tumor and certain specific properties of the cancer cells, which release substances that inappropriately activate blood coagulation, favoring thrombosis.
One must also bear in mind that the activation of the coagulation system favors tumor growth. This sets in motion a vicious cycle in which the mechanisms of thrombosis contribute to the progression of the cancer.

Venous thrombosis has far-reaching effects on a patient’s quality of life and prognosis. Thrombosis is, in fact, the second cause of death – after the tumor itself – among these patients, with often dramatic consequences on the quality of their lives and their life expectancy. Besides their greater risk of venous thrombosis or pulmonary embolism, patients with cancer also have a higher risk of relapsing thrombosis or hemorrhage while receiving anticoagulative therapy to cure the thrombosis. The probability of re-hospitalization within 6 months after an episode of thrombosis is 22% for cancer patients, compared to 6.5% for patients without a tumor.

Preventing venous thrombosis in patients with cancer is fundamental for several reasons: once the thrombosis has happened it is hard to manage the anticoagulant therapy because of the substantial risk of hemorrhage, and anticoagulants are not very effective and raise the risk of relapse.
Recent evidence indicates that in a patient with cancer, thromboprophylaxis should be considered when there are conditions that raise the risk of thrombosis – these include surgery, prolonged immobilization and antitumoral therapy.