The plot to clot – Deep vein thrombosis

Dr Jasmine Ramiah expands on deep vein thrombosis in cancer.

For most people, a cancer diagnosis brings a flood of new information and unfamiliar medical jargon in addition to the emotions.

One important but often overlooked complication of cancer is the increased risk of developing blood clots or thrombosis, particularly a condition called deep vein thrombosis (DVT).

Understanding why and how this happens, how to recognise the warning signs, and what can be done about it can help you feel more informed and empowered during your cancer journey.

What is a DVT?

A DVT occurs when a blood clot forms in a deep vein, most commonly in the leg, but sometimes in the arm or blood vessels within the body. The danger of a DVT lies not only in the clot itself, but in the possibility that part of it can break off and disseminate to the lungs, causing a pulmonary embolus (PE) which is a serious and potentially life-threatening condition that requires urgent medical attention.

Cancer increases the risk

If you’re living with cancer, you’re at a significantly higher risk of developing blood clots than the general population owing to the biology of the malignancy.

Cancer can alter the body’s normal clotting mechanisms, increasing the propensity for thrombus formation. In addition, many cancer treatments contribute to this risk. Chemotherapy, targeted therapies, and hormonal treatments can affect how blood flows and clots. Surgery, hospital admissions, reduced mobility, dehydration, and the use of central lines or ports for the administration of chemotherapeutic agents can further increase the likelihood of thrombus formation.

While certain cancers (pancreatic, lung, stomach, and brain cancers) are known to carry a particularly higher risk to developing thrombus, blood clots can occur in patients with any type of cancer.

Symptoms

Symptoms can sometimes be subtle and easy to miss, however, variable and patient specific. You may notice swelling in one leg or arm, pain or tenderness that may feel like a cramp or muscle strain, or warmth and redness of the skin over the affected area.

A PE may cause sudden shortness of breath, chest pain that worsens with deep breathing, a rapid heartbeat (tachycardia), dizziness, or coughing up blood (haemoptysis). Urgent medical attention should be sought, should these symptoms arise.

Diagnosis

Diagnosing a blood clot usually involves imaging modalities, such as a doppler ultrasound to detect thrombi within the deep vessels of the limbs, while a CT scan may be performed if a PE is suspected.

Blood tests can also help guide doctors, such as a coagulation screen including a D-dimer, but imaging is essential for confirming the diagnosis.

A D-dimer test is incidentally elevated in the presence of cancer and hospitalised patients.

Treatment

Treatment in patients with cancer focuses on preventing the clot from growing, reducing the risk of it disseminating to the lungs, and stopping new clots from forming. This is usually done with blood-thinning medications, referred to as anticoagulants, which may be administered through several routes, such as oral, intravenously, or subcutaneously.

The choice of administration will be determined by the clinician and depends on patient expectations and comorbidities or other risk factors. In some cases, injections are preferred because they may be safer or more effective with certain cancers or treatments.

Treatment typically continues for several months and sometimes for as long as the cancer remains active.

The choice of medication, route of administration, and duration of treatment is carefully tailored to each patient, taking into account the type of cancer, bleeding risk, renal function, and other drug interactions.

While not all blood clots can be prevented, there are practical steps that can reduce the risk. Staying as mobile as possible, even with gentle walking, helps improve circulation. Staying hydrated through consuming enough liquids to avoid dehydration is important, especially during treatment. You may be advised to wear compression stockings or to take preventative blood thinners during high-risk periods, such as after surgery or during hospital stays.

Most importantly, you should feel encouraged and supported to report any new or unusual symptoms to your healthcare team without delay.

Dr Jasmine Ramiah is a clinical haematology subspecialist at Inkosi Albert Luthuli Central Hospital. She expanded her expertise and qualified as a haematopathologist in 2024. This dual training has sharpened her diagnostic acumen and enriched her clinical perspective, allowing her to integrate precise pathology insights with patient-centred haematology care.

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