Cancer-Associated Thrombosis

Who this is for: Haematology trainees, medical registrars, and clinicians managing adult patients with cancer-associated venous thromboembolism (VTE) in inpatient and outpatient settings.

This guideline covers

• Diagnosis of DVT and PE in patients with active malignancy
• Anticoagulant selection for treatment of established cancer-associated thrombosis (CAT)
• Duration of anticoagulation in CAT
• Pharmacological thromboprophylaxis in ambulatory and hospitalised cancer patients
• Management of recurrent VTE and special clinical situations

This guideline does not cover

• Management of VTE unrelated to malignancy — see NICE NG158 for general VTE
• Inherited thrombophilia — see BSH Thrombophilia Guideline
• Arterial thromboembolism in cancer
• Paediatric oncology patients

Definition

Cancer-associated thrombosis (CAT) refers to venous thromboembolism — including deep vein thrombosis (DVT), pulmonary embolism (PE), splanchnic vein thrombosis, and upper limb DVT — occurring in the setting of active malignancy or its treatment.

Clinical Relevance

VTE will complicate the clinical course of approximately 1 in 20 cancer patients, with estimates in high-risk malignancies reaching considerably higher.^[2,3] It is a leading cause of death in cancer patients after disease progression itself. Cancer confers approximately a fourfold increase in VTE risk compared with the general population,^[2] rising to 6.5-fold with concurrent chemotherapy.^[4] This risk is further amplified by surgery and central venous catheters.

Pathophysiology

CAT arises through disruption of all three components of Virchow's triad: hypercoagulability (tumour-derived tissue factor expression, mucin-mediated platelet activation, procoagulant microparticle release), endothelial injury (from chemotherapy, radiation, or direct tumour invasion), and venous stasis (from immobility, compression by lymphadenopathy or tumour mass, or reduced cardiac output).

Highest-risk cancer types

• Pancreatic cancer — highest absolute VTE risk
• Primary and metastatic brain tumours
• Stomach, kidney, lung, ovarian, and haematological malignancies
• Mucin-secreting adenocarcinomas — particularly prothrombotic due to non-immune platelet activation

Initial Assessment

History

• Onset and site of symptoms — limb swelling, pain, erythema (DVT); dyspnoea, pleuritic chest pain, haemoptysis, palpitations (PE)
• Cancer type, current treatment, recent surgery, and CVC presence
• Prior VTE history and thromboprophylaxis use
• Current anticoagulation and bleeding history

Examination

• DVT: unilateral limb swelling, erythema, warmth, tenderness; apply Wells DVT score
• PE: tachycardia, tachypnoea, hypoxia, signs of right heart strain; apply Wells PE score or PERC
• Haemodynamic status — distinguish massive PE from sub-massive/non-massive PE

Investigations

First-line

• Suspected lower limb DVT: Whole-leg compression ultrasound (USS)
• Suspected PE: CT pulmonary angiography (CTPA) — preferred in cancer patients due to frequent lung parenchymal changes on V/Q scan
• Baseline bloods: FBC, renal function, LFTs, clotting screen — essential before starting anticoagulation

Second-line / additional

• Bilateral leg USS when PE confirmed — may identify DVT and inform monitoring
• Echocardiography — if haemodynamically unstable or signs of right heart strain on CTPA
• V/Q scan — alternative when CTPA contraindicated (contrast allergy, severe renal impairment)

Incidental VTE

VTE detected incidentally on staging or follow-up CT (not clinically suspected) should be managed as symptomatic VTE.^[2,3] Evidence indicates equivalent recurrence risk. Do not observe without treatment in patients with active cancer.

The Khorana score is the validated tool for identifying ambulatory cancer patients at high risk of VTE prior to initiating systemic therapy.^[4] Developed and validated in a prospective cohort of 2,701 patients, it predicts VTE risk over the first 2.5 months of chemotherapy.^[4] It is recommended by ASCO 2023^[3] and BSH 2024^[2] to guide prophylaxis decisions in the outpatient setting.

For hospitalised patients, standard inpatient VTE risk assessment tools (e.g., NICE-recommended inpatient risk assessment) should be used rather than the Khorana score.^[1]

Anticoagulant Options

All three options below are acceptable first-line anticoagulants for CAT. The choice depends on cancer type, bleeding risk, drug interactions, platelet count, and patient preference.

Direct oral anticoagulants (DOACs)

• Apixaban — 10 mg twice daily for 7 days, then 5 mg twice daily. No requirement for initial parenteral bridging. Preferred DOAC in cancer-associated VTE based on the CARAVAGGIO trial (NEJM 2020)^[5] — a Phase III RCT showing non-inferiority to dalteparin with comparable major bleeding rates.^[2,3]
• Edoxaban — 60 mg once daily (30 mg once daily if CrCl 15–50 mL/min, body weight ≤60 kg, or concurrent P-gp inhibitor). Requires 5–10 days of initial LMWH before switching.

Low-molecular-weight heparin (LMWH)

• Dalteparin, enoxaparin, or tinzaparin — weight-based therapeutic dosing (refer to local formulary and renal dose adjustment guidelines)
• Preferred agent when DOACs are contraindicated or in higher bleeding-risk situations
• Subcutaneous administration — consider patient acceptability for long-term use

Duration of Anticoagulation

• Minimum 6 months of therapeutic anticoagulation for all cancer-associated VTE
• Continue anticoagulation beyond 6 months while cancer remains active or systemic treatment is ongoing — review at 6 months with multidisciplinary input^[2]
• If cancer achieves complete remission: reassess need to continue at 6 months; stopping may be appropriate on an individual basis
• Reassess at every clinical review — anticoagulation in cancer is dynamic; bleeding risk and cancer status change over time

Recurrent VTE on Therapeutic Anticoagulation

• First, verify adherence to treatment and confirm correct therapeutic dose
• If recurrence occurs on a DOAC: switch to therapeutic LMWH
• If recurrence occurs on LMWH at therapeutic dose: escalate LMWH dose by 20–25% (supertherapeutic dosing), with subsequent management guided by clinical response^[2]
• Seek specialist haematology input for recurrence on optimal anticoagulation

Ambulatory Cancer Patients on Systemic Therapy

• Calculate Khorana score before initiating systemic therapy
• Score ≥ 2: offer pharmacological thromboprophylaxis — apixaban 2.5 mg twice daily or rivaroxaban 10 mg once daily are preferred oral options^[3]; LMWH at prophylactic dose is an alternative
• Score 0–1: routine prophylaxis not recommended; individual risk discussion appropriate
• Reassess regularly — cancer stage, treatment, and patient factors evolve

Hospitalised Cancer Patients

• Perform VTE risk assessment on admission using a validated tool
• Offer LMWH prophylaxis to all medically ill cancer patients unless contraindicated (active bleeding, platelets < 50, recent surgery with high haemorrhagic risk)
• Continue for duration of hospital admission; reassess if clinical status changes
• Anti-embolism stockings and intermittent pneumatic compression as adjuncts when pharmacological prophylaxis is contraindicated

Surgical Cancer Patients

• LMWH prophylaxis perioperatively and postoperatively in all cancer surgery patients
• Extended LMWH prophylaxis for 28 days after major open abdominal or pelvic cancer surgery — reduces risk of post-discharge VTE^[1,2]
• Mechanical prophylaxis (anti-embolism stockings, IPC) perioperatively, continued until ambulatory

Visual pathway for anticoagulant selection in confirmed cancer-associated VTE. Based on BSH 2024 and ASCO 2023.^[2,3] Scroll horizontally on smaller screens.

The following framework is designed to guide anticoagulant selection in common clinical scenarios. It supports — but does not replace — individual clinical judgement and multidisciplinary discussion.

Haemodynamically unstable PE

Thrombolysis criteria in cancer patients are the same as in non-cancer patients — haemodynamic instability is the primary indication. Prognosis of massive PE in cancer is very poor; early resuscitation, senior clinical involvement, and multidisciplinary decision-making are essential.

Brain tumours (primary or metastatic)

The risk of intracranial haemorrhage must be weighed carefully against the risk of VTE recurrence. LMWH is generally preferred over DOACs in this setting. Decisions should involve the oncology, neurosurgery, and haematology teams. Each patient should be assessed individually.

Concurrent thrombocytopenia

When platelet counts are significantly reduced due to chemotherapy or disease, anticoagulation should be individualised. BSH 2024 guidance advises that during acute CAT, anticoagulation should be avoided if platelet count cannot be maintained above 25 × 10⁹/L.^[2] Between 25–50 × 10⁹/L, use with caution after haematology review. Platelet transfusion support may be required to enable anticoagulation in high-risk scenarios.

Drug–drug interactions with systemic therapy

Several targeted cancer therapies are inhibitors or inducers of P-glycoprotein (P-gp) and CYP3A4, which can significantly affect DOAC plasma levels. Review drug interactions before prescribing any DOAC alongside tyrosine kinase inhibitors, CDK4/6 inhibitors, or azole antifungals. LMWH does not carry the same interaction risk.

Cancer entering remission

In patients who achieve complete remission following cancer treatment, reassess the need for continued anticoagulation at the 6-month review. Stopping anticoagulation may be appropriate if the cancer is in remission and there is no ongoing high-risk treatment, particularly if VTE was provoked by a now-resolved risk factor such as surgery or hospitalisation.

The following measurable standards support clinical audit, local governance review, and quality improvement. They are aligned with recommendations in NICE NG158, BSH 2024, and ASCO 2023.

Update Plan

This guideline summary will be reviewed when any of the following occur: (1) publication of an updated BSH Cancer-Associated Thrombosis guideline; (2) major NICE update to NG158 relevant to CAT; (3) publication of a landmark RCT altering current anticoagulant recommendations in CAT. In the absence of these triggers, a scheduled review will be undertaken no later than April 2028.

This summary is based on the following published guidelines and primary trial evidence. References [1]–[3] are the core guideline sources. Reference [4] is the original Khorana score validation study. Reference [5] is the primary RCT supporting apixaban as the preferred DOAC in CAT. All recommendations should be interpreted in the context of local formulary availability, individual patient factors, and current institutional policy.

• [1]
  Venous thromboembolic diseases: diagnosis, management and thrombophilia testing A1 — NICE Clinical Guideline

  NICE Guideline NG158. Published March 2020, updated August 2023. Available at nice.org.uk/guidance/ng158
• [2]
  Cancer-associated venous thrombosis in adults (second edition): A British Society for Haematology Guideline A1 — Society Guideline

  Alikhan R, Gomez K, Maraveyas A, Noble S, Young A, Thomas M; British Society for Haematology. British Journal of Haematology 2024;205(1):71–87. DOI: 10.1111/bjh.19414. PMID: 38664942. Systematic evidence review and GRADE-based recommendations. Available at b-s-h.org.uk/guidelines
• [3]
  Venous Thromboembolism Prophylaxis and Treatment in Patients With Cancer: ASCO Guideline Update A1 — Society Guideline

  Key NS, Khorana AA, Kuderer NM, et al. Journal of Clinical Oncology 2023;41(16):3063–3071. DOI: 10.1200/JCO.23.00294. PMID: 37075273. Available at asco.org/guidelines
• [4]
  Development and validation of a predictive model for chemotherapy-associated thrombosis A2 — Primary derivation/validation cohort study

  Khorana AA, Kuderer NM, Culakova E, Lyman GH, Francis CW. Blood 2008;111(10):4902–4907. DOI: 10.1182/blood-2007-10-116327. PMID: 18216292. Original derivation and validation cohort study for the Khorana risk score (n=2,701).
• [5]
  Apixaban for the Treatment of Venous Thromboembolism Associated with Cancer (CARAVAGGIO) A2 — Phase III RCT

  Agnelli G, Becattini C, Meyer G, et al. New England Journal of Medicine 2020;382(17):1599–1607. DOI: 10.1056/NEJMoa1915103. PMID: 32223112. Phase III RCT; apixaban non-inferior to dalteparin for recurrent VTE; major bleeding rates comparable.