Cancer-associated thrombosis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Cancer-associated thrombosis includes deep-vein thrombosis, pulmonary embolism, upper-extremity catheter thrombosis and less common splanchnic or cerebral venous events. Malignancy creates a sustained hypercoagulable state through tissue factor, thrombin, platelets, neutrophil traps and endothelial activation. Surgery, chemotherapy, hormonal treatment, hospitalisation, immobility and central lines add local injury and stasis. Risk varies by tumour: pancreatic, gastric, brain, lung and advanced metastatic cancers are particularly thrombogenic, but any active cancer can be complicated by VTE.

Presentation can be non-specific because cancer itself causes swelling, pain, hypoxaemia and tachycardia. Use the standard physiological and probability-based pathway rather than assuming every symptom is tumour progression. Proximal compression ultrasound is the first-line DVT study; CTPA is the usual first-line PE examination, with V/Q imaging in selected contrast or radiation circumstances. D-dimer is frequently positive from cancer and treatment, but a negative result may still exclude VTE when the patient genuinely meets a validated low-probability route. Incidental proximal DVT or segmental PE generally receives the same clinical assessment as symptomatic disease.

Anticoagulant choice is shared and dynamic. Direct oral anticoagulants are convenient and effective for many people with active cancer, but gastrointestinal or genitourinary mucosal tumours, vomiting, malabsorption, interacting anticancer agents, renal or liver dysfunction and imminent procedures may favour low-molecular-weight heparin. Brain metastasis is not an automatic exclusion, but tumour histology, recent bleeding and imaging matter. Thrombocytopenia requires a platelet-specific strategy with oncology or haematology rather than unstructured half dosing.

Treatment duration is longer than a simple transient provocation. NICE advises 3 to 6 months initially, with review of active disease, current treatment, bleeding and patient preference. Many continue while cancer remains active and recurrence risk outweighs bleeding. Recurrent VTE despite verified treatment prompts adherence, absorption, interactions, heparin-induced thrombocytopenia and tumour progression review before changing intensity. IVC filters are exceptional and should be removed when anticoagulation can resume.

Key points

Cancer increases thrombosis through tumour procoagulants, inflammation, platelets, stasis, surgery, systemic therapy and central venous devices; risk persists while cancer is active.
Key presentations are unilateral leg or arm swelling and pain, unexplained breathlessness, pleuritic pain, haemoptysis, syncope or catheter dysfunction; fever does not exclude clot.
First-line DVT imaging is proximal leg-vein ultrasound and first-line PE imaging is CTPA when suitable; D-dimer is often raised by cancer and is useful only within a validated low-probability algorithm.
Do not delay therapeutic anticoagulation in a likely VTE when imaging is delayed and bleeding risk is acceptable; obtain diagnostic confirmation as soon as possible.
NICE recommends considering a direct-acting oral anticoagulant for confirmed proximal DVT or PE in active cancer, but tumour site, interactions, absorption, renal function and procedures determine whether LMWH is safer.
Luminal gastrointestinal or genitourinary cancer, severe thrombocytopenia, intracranial disease and active bleeding require individual specialist selection and sometimes dose interruption or modification.
Treat for at least 3 to 6 months and review continuation while cancer or anticancer treatment remains active; a calendar stop date must not replace recurrence and bleeding reassessment.
Do not use an inferior vena cava filter routinely; reserve it for selected acute VTE when anticoagulation is genuinely contraindicated or has failed after review, with a retrieval plan.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Tumour-driven hypercoagulability

Cancer cells express tissue factor and inflammatory mediators, activate platelets and endothelium and release procoagulant extracellular vesicles.

Treatment and device exposure

Surgery, systemic therapy, hormonal treatment, antiangiogenic drugs and central venous catheters add endothelial injury and immobility.

Venous stasis

Hospitalisation, reduced mobility, tumour compression and heart or respiratory failure slow flow and favour lower-limb or device-associated clot.

Individual susceptibility

Previous VTE, inherited thrombophilia, older age, obesity, infection, renal disease and high-risk pancreatic, gastric, brain or lung cancer modify risk.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Coagulation is persistently activated
Tumour tissue factor and cytokines generate thrombin continuously, while natural anticoagulant and fibrinolytic control becomes insufficient.
2
Platelets and neutrophils scaffold clot
Activated platelets, monocytes and neutrophil extracellular traps provide phospholipid and DNA surfaces on which fibrin and cells accumulate.
3
Local flow determines site
Stasis behind tumour or within a catheterised vein concentrates activated factors and permits thrombus propagation along deep venous channels.
4
Emboli obstruct pulmonary circulation
Detached clot increases pulmonary vascular resistance, strains the right ventricle and can reduce left-heart preload and systemic perfusion.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Lower-limb DVT

New unilateral swelling, pitting oedema, calf or thigh pain and venous distension in cancer requires objective venous imaging.

Pulmonary embolismRed flag

Unexplained dyspnoea, pleuritic pain, tachycardia, hypoxaemia, haemoptysis or syncope can occur with a normal chest examination.

High-risk PERed flag

Hypotension, shock, altered consciousness, severe hypoxaemia or right-heart failure indicates threatened circulation and possible reperfusion need.

Catheter-related thrombosis

Arm, shoulder or neck swelling, line pain, collateral veins or failure to aspirate suggests upper central venous thrombosis.

Unusual-site thrombosis

Abdominal pain, portal hypertension, headache or neurological change may reflect splanchnic or cerebral venous thrombosis requiring site-specific imaging.

Anticoagulant bleeding

New bleeding, bruising, anaemia, headache or haemodynamic change during treatment requires urgent source and severity assessment.

Red flags requiring action

Hypotension, rising lactate, syncope, severe hypoxaemia or right-ventricular strain suggests high-risk pulmonary embolism.
A tense cyanotic painful leg, sensory loss or weak arterial signals suggests phlegmasia and threatened limb viability.
New headache, neurological deficit or reduced consciousness before anticoagulation raises intracranial metastasis, haemorrhage or stroke and changes immediate risk.
Haematemesis, melaena, haematuria, falling haemoglobin or severe thrombocytopenia requires an explicit bleeding-versus-thrombosis decision rather than automatic cessation or continuation.
Catheter dysfunction, unilateral arm or neck swelling and collateral veins raises upper-extremity thrombosis or central venous obstruction.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line proximal leg-vein ultrasoundFirst stepFirst line
Why
Confirm or exclude clinically suspected proximal lower-limb DVT without contrast or radiation.
Interpretation and limitations
A non-compressible proximal segment confirms DVT. If the initial scan is negative but clinical probability remains high, follow the NICE repeat-imaging branch.
02
First-line CT pulmonary angiographyFirst line
Why
Demonstrate pulmonary arterial thrombus and assess right heart and alternative thoracic causes.
Interpretation and limitations
Use V/Q imaging when contrast or radiation considerations favour it; a technically limited negative CTPA does not settle persistent high probability.
03
ECG, troponin, natriuretic peptide and echocardiography
Why
Risk-stratify confirmed PE and identify right-ventricular pressure overload or another cardiac emergency.
Interpretation and limitations
These assess severity rather than diagnosing PE alone; shock with RV dysfunction prompts urgent reperfusion-team discussion.
04
FBC, renal, liver and coagulation profile
Why
Select and dose anticoagulation and detect cytopenia, organ dysfunction and baseline bleeding risk.
Interpretation and limitations
Platelet trajectory and creatinine clearance can change rapidly during treatment; repeat before procedures and when illness or anticancer therapy changes.
05
Medication and cancer interaction review
Why
Identify CYP or P-glycoprotein interactions, poor absorption and tumour-site bleeding risk before choosing an oral agent.
Interpretation and limitations
Check the complete systemic-treatment protocol, supportive medicines and over-the-counter products; an interaction may favour LMWH.
06
Repeat or alternative imaging for recurrence
Why
Distinguish new clot from residual chronic abnormality when symptoms recur during anticoagulation.
Interpretation and limitations
Compare with baseline images and verify adherence and dose; persistent filling defects alone do not prove treatment failure.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Lymphoedema or venous compression

Nodal disease, surgery and radiotherapy cause chronic limb swelling without acute intraluminal clot; ultrasound and CT clarify coexistence.

Cellulitis or treatment inflammation

Warm erythema, fever and tenderness can reflect infection, radiation or infusion reaction, but do not safely exclude simultaneous DVT.

Heart failure or pleural disease

Cancer-related effusion, pneumonia and cardiac dysfunction cause breathlessness and hypoxaemia and may coexist with pulmonary embolism.

Tumour thrombus

Renal, hepatic and other cancers can extend viable tumour into veins; enhancement and continuity with the mass alter surgical and anticoagulant planning.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Suspected VTEImage promptly and anticoagulate safelyFirst stepA cancer patient develops a compatible limb, chest or catheter symptom.

1Assess haemodynamic and bleeding risk, use the validated DVT or PE probability pathway and obtain ultrasound or CTPA without attributing symptoms automatically to malignancy.
2Start interim therapeutic anticoagulation if clinical probability is significant and imaging is delayed, after platelet, renal, bleeding and procedure assessment.
3Confirm diagnosis and anatomical extent, then document the agent, dose, monitoring, interaction and early review plan.

02Select treatmentMatch anticoagulant to tumour and patientImaging confirms proximal DVT or pulmonary embolism while malignancy is active.

1Compare a direct oral anticoagulant with LMWH using tumour site, mucosal bleeding, platelets, renal and liver function, absorption, interactions, injections and patient preference.
2Use a full licensed acute regimen rather than omitting the loading phase, unless a specialist thrombocytopenia or bleeding protocol explicitly modifies treatment.
3Review after clinical stabilisation and at every cancer-treatment change because an initially appropriate agent may become unsafe during surgery, vomiting or interaction.

03ComplicatedManage bleeding or recurrenceMajor bleeding, severe thrombocytopenia or objectively recurrent VTE occurs during anticoagulation.

1Stabilise bleeding and identify site, timing, last dose, renal clearance and reversal option while protecting against unnecessary prolonged interruption.
2For thrombocytopenia, use the haematology platelet-threshold and transfusion strategy matched to clot acuity and bleeding rather than an arbitrary universal half dose.
3For recurrence, verify diagnosis, adherence, absorption, interaction and correct dosing and then switch or intensify therapy with thrombosis expertise.

04Long termReview beyond the initial courseThree to six months of treatment is approaching completion.

1Reassess cancer activity, systemic therapy, recurrence, bleeding, organ function, quality of life and patient preference rather than stopping automatically.
2Continue anticoagulation when active cancer risk remains greater than bleeding, with a defined interval for repeat review.
3Stop when the balance changes, providing recurrence symptoms and a plan for future surgery, admissions and prophylaxis.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Provides an oral single-drug regimen for suitable active-cancer VTE without a heparin lead-in.

Apixaban

Give 10 mg orally twice daily for 7 days, then 5 mg twice daily for treatment of acute DVT or PE; any reduction after 6 months is a deliberate recurrence-versus-bleeding decision under the cancer thrombosis plan.

Avoid active clinically significant bleeding and review renal and liver function, strong CYP3A4 or P-glycoprotein interactions, luminal tumour, thrombocytopenia, vomiting, procedures and neuraxial timing.

Provides predictable parenteral anticoagulation when oral absorption, interaction or mucosal bleeding makes a direct oral agent less suitable.

Low-molecular-weight heparin

Use the product-specific weight-based treatment regimen; for dalteparin in cancer-associated VTE a licensed course uses 200 IU/kg subcutaneously once daily for the first 30 days, then approximately 150 IU/kg once daily for months 2 to 6, subject to product maximums and platelet or renal adjustment.

Check actual weight, creatinine clearance and platelets, monitor bleeding and heparin-induced thrombocytopenia and plan procedures and neuraxial anaesthesia carefully; accumulation can occur in renal failure.

Reduces active anticoagulant effect during life-threatening or uncontrolled bleeding without assuming laboratory normalisation alone provides source control.

Anticoagulant reversal for major bleeding

Use the current agent-specific emergency reversal protocol based on anticoagulant, last dose, renal function, bleeding site and severity, alongside blood-product and procedural haemostasis.

Reversal can increase thrombosis in an already hypercoagulable patient. Document when and how prophylactic or therapeutic anticoagulation will be reconsidered after haemostasis.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Recurrent venous thromboembolism

Active tumour and treatment maintain thrombin generation, so recurrence remains higher than in provoked non-cancer VTE even during anticoagulation.

Major bleeding

Anticoagulation can expose friable luminal tumour, intracranial lesions, thrombocytopenia and procedure sites, causing gastrointestinal, urinary or cerebral haemorrhage.

Post-thrombotic morbidity

Persistent venous obstruction and valve damage cause chronic swelling, pain, ulceration and reduced mobility after lower- or upper-limb thrombosis.

Chronic thromboembolic pulmonary disease

Unresolved embolic obstruction can produce persistent dyspnoea, exercise limitation, pulmonary hypertension and progressive right-heart strain over time.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review symptoms and observations early after treatment and escalate any shock, increasing oxygen need, limb cyanosis or neurological change.
Check blood count, platelets, renal and liver function at baseline and when systemic therapy, acute illness, weight or bleeding risk changes.
At each review, verify exact agent, dose, loading phase, adherence, vomiting, absorption, interactions and upcoming invasive procedures.
Ask directly about gastrointestinal, urinary, uterine and neurological bleeding and trend haemoglobin rather than relying on visible bruising alone.
Reassess continuation at 3 to 6 months and repeatedly while cancer remains active, documenting why recurrence or bleeding risk predominates.
For an IVC filter, record indication, retrieval owner and date and restart anticoagulation when the contraindication resolves.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Cancer makes D-dimer noisy

A positive result is common from tumour and treatment; its value remains mainly within a genuinely low-probability rule-out pathway.

The best drug can change

Surgery, vomiting, thrombocytopenia and new interacting therapy can make a previously convenient oral anticoagulant temporarily unsuitable.

Incidental does not mean trivial

An unsuspected proximal or segmental event on staging imaging needs the same symptom, bleeding and treatment assessment as a clinically suspected event.

Brain metastasis is nuanced

Intracranial disease does not automatically prohibit anticoagulation, but recent haemorrhage, histology, lesion burden and current imaging determine risk.

Filters need an exit plan

A temporary mechanical substitute can itself thrombose, and leaving it indefinitely without reassessment creates avoidable long-term harm.

11Common pitfallsFrequent interpretation and management errors.

01
Using a positive D-dimer as confirmation of VTE in active cancer.
02
Prescribing a direct oral anticoagulant without checking anticancer interactions and luminal tumour bleeding risk.
03
Omitting the acute loading phase of apixaban without a documented specialist reason.
04
Stopping anticoagulation automatically at three or six months despite ongoing active cancer.
05
Reducing or withholding treatment for thrombocytopenia without considering clot acuity and a platelet-supported strategy.
06
Diagnosing recurrent VTE from residual chronic imaging without comparison and adherence review.
07
Inserting an IVC filter without a clear contraindication to anticoagulation and retrieval plan.