Blood clots are a significant concern for individuals with cancer. A blood clot is essentially a mass formed when blood platelets, proteins, and cells stick together, which is a natural process for stopping bleeding after an injury. However, when these clots form without injury or do not dissolve properly, they can block blood flow and lead to serious health complications. This abnormal clotting, known as cancer-associated thrombosis (CAT), represents a major cause of illness and death in cancer patients, second only to the cancer itself. Up to 20% of people with cancer may develop a blood clot at some point during their disease.
Cancers Strongly Linked to Clot Formation
Certain types of cancer carry a higher predisposition for blood clot development. Among solid tumors, cancers of the pancreas, stomach, lung, colon, brain, kidney, and ovaries are particularly associated with an elevated risk. Pancreatic cancer, in particular, exhibits one of the highest rates of cancer-associated thrombosis among all solid tumors, with approximately 7.4% of patients experiencing venous thromboembolism within a year of diagnosis.
Hematological malignancies, which are cancers of the blood, bone marrow, and lymph nodes, also pose a substantial risk for clotting. These include lymphomas, leukemias, and multiple myeloma. The aggressiveness of the cancer and its stage, especially if it has spread to other parts of the body (metastatic cancer), further increases the likelihood of clot formation. For instance, advanced pancreatic cancer significantly elevates the risk of blood clots. The tendency for these specific cancers to cause clots can be attributed to factors such as their ability to release clot-promoting substances, their anatomical location, and the inflammatory responses they induce.
How Cancer Promotes Clotting
Cancer promotes blood clot formation through several complex biological mechanisms. Cancer cells themselves can directly activate the body’s clotting cascade. They achieve this by releasing procoagulant factors, such as tissue factor, which initiate the complex series of events that lead to clot formation.
Tumors can also interact with the walls of blood vessels, causing damage or dysfunction to the endothelial lining. This damage creates sites where clots are more likely to form. Furthermore, cancer often triggers a systemic inflammatory response in the body. This inflammation releases various inflammatory cytokines and can lead to the production of tumor-derived microparticles, both of which contribute to a state of hypercoagulability and promote clotting. Cancer patients also tend to have “sticky blood” because cancer cells can stimulate the production of clotting factors, which are proteins that help blood clot.
Common Locations and Types of Clots
The most common and serious types of blood clots experienced by cancer patients are venous thromboembolism (VTE). This term encompasses two primary conditions: deep vein thrombosis (DVT) and pulmonary embolism (PE). A deep vein thrombosis is a blood clot that forms in a deep vein, most frequently in the legs, particularly the calf or thigh, but can also occur in the arms. Symptoms of DVT in a limb can include swelling, pain, warmth, and redness in the affected area.
A pulmonary embolism occurs when a piece of a DVT breaks off and travels through the bloodstream to the lungs, where it can block blood flow. This is a potentially life-threatening condition. Symptoms of a pulmonary embolism include sudden breathlessness, chest pain that worsens with breathing, and sometimes coughing up blood. While less common than venous clots, arterial clots, which can lead to heart attacks or strokes, can also affect cancer patients.
Factors Increasing Clot Risk in Cancer Patients
Beyond the specific type of cancer, several other factors can significantly increase a patient’s risk of developing blood clots. Cancer treatments are a major contributor, including chemotherapy, which can damage blood vessels and alter clotting proteins, and hormonal therapies like tamoxifen. Targeted therapies and immunotherapies have also been linked to an increased risk of blood clots, with some studies indicating that up to 25% of cancer patients receiving immunotherapy may experience VTE. Surgical procedures, especially those involving the abdomen or pelvis, and radiation therapy can also heighten the risk due to tissue injury and immobility.
Patient-specific factors also play a role in clot risk. Older age, immobility, and obesity are known to increase the likelihood of clot formation in cancer patients. Conditions such as a history of previous blood clots, certain inherited clotting disorders, and other medical conditions like heart disease, kidney disease, or infections can further elevate this risk. The presence of central venous catheters, often used for administering chemotherapy, can also serve as sites for clot formation. It is often a combination of these patient, tumor, and treatment-related factors that collectively increases a cancer patient’s susceptibility to blood clots.