Venous Thromboembolism — Blood Clots in Veins

Venous thromboembolism (VTE) is a pathological condition characterised by the inappropriate formation of a thrombus within the venous circulation. When a clot obstructs blood flow in deep veins, typically within the lower limbs or pelvis, it is termed deep vein thrombosis. If fragments dislodge, they can migrate through the heart into the pulmonary arterial bed, causing a potentially life-threatening pulmonary embolism.

Malignancy significantly increases VTE risk through multiple mechanisms, often termed Virchow's triad. Tumours can release pro-coagulant substances, physically compress major veins, and induce systemic inflammation. Furthermore, systemic anti-cancer therapies, central venous catheters, surgical interventions, and extended periods of immobility collectively amplify the likelihood of abnormal clot formation in oncology patients.

VTE is a frequent and serious complication of malignancy that can interrupt essential cancer treatments. Experiencing a clot often requires hospital assessment, delays in planned chemotherapy or surgery, and long-term anticoagulation therapy. Recognising early symptoms ensures rapid treatment, reducing the likelihood of severe respiratory compromise or chronic venous damage. Understanding clot risk helps patients and carers remain vigilant, adopt preventative habits like staying hydrated and mobile, and seek emergency care promptly when warning signs appear.

VTE is evaluated through imaging and blood tests. A D-dimer blood test measures clot breakdown products, though it is frequently elevated in cancer regardless of clots. Suspected deep vein thrombosis is typically diagnosed using compression venous ultrasonography. If pulmonary embolism is suspected, a computed tomography pulmonary angiogram (CTPA) or ventilation-perfusion (V/Q) scan is performed to visualise blockages in pulmonary vessels.

Venous thromboembolism can occur alongside any malignancy, but risk varies significantly by tumour type. It is particularly common in advanced pancreatic, gastric, brain, ovarian, and lung cancers. Haematological malignancies, such as multiple myeloma—especially when treated with immunomodulatory drugs and steroids—also carry heightened risks. Metastatic disease across almost all cancer types substantially elevates susceptibility compared to early-stage disease.

Confirmed VTE is treated with anticoagulants, most commonly low-molecular-weight heparin or direct oral anticoagulants such as apixaban or rivaroxaban. Treatment usually lasts at least three to six months, or as long as the cancer remains active. In hospitalised surgical patients, prophylactic blood thinners or mechanical compression devices are routinely employed to prevent clots from forming.