What causes blood clots in cancer?

Cancer can change the balance between clot-forming and clot-limiting processes in the blood. Tumour cells may release signals that make clotting more active and may interact with blood vessel walls. Inflammation, dehydration, surgery, hospital stays, and time spent sitting or lying down can add further strain on this system.

Pancreatic cancer is associated with cancer-associated thrombosis, but a clot can occur with many cancers. A clot may form in a deep vein, often in a leg, or travel to the lungs. Some clots cause few early symptoms, so new changes should be taken seriously.

Contact your cancer team promptly about one-sided leg swelling, pain, warmth, or redness; an unexplained tender arm; or a new heavy feeling in a limb. Tell them about recent surgery, a line or port, reduced activity, vomiting, diarrhoea, or difficulty drinking.

Do not start aspirin or another blood thinner without medical advice. If a clot is suspected, assessment may include an examination and tests or imaging. If treatment is prescribed, take it exactly as directed and report bleeding, black stools, blood in urine, or severe bruising.

Call emergency services for sudden shortness of breath, chest pain that worsens with breathing, coughing blood, fainting, severe dizziness, or a fast irregular heartbeat. These may indicate that a clot has travelled to the lungs and require immediate assessment.

Ask what clot symptoms to watch for, whether your cancer or treatment changes your risk, and what to do if you miss a blood-thinner dose. Ask how to balance movement, hydration, procedures, and bleeding precautions during treatment.