# Blood clot risk assessment and preventive anticoagulation during outpatient cancer treatment

Source: https://onco.cc/protocols/vte-risk-assessment-and-thromboprophylaxis-ambulatory/  
OnCo record `vte-risk-assessment-and-thromboprophylaxis-ambulatory` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Cancer and its treatment raise the chance of a blood clot in a leg or lung. Most people having treatment as outpatients do not need a blood thinner, but some do: your team can work out your risk with a simple score from your blood count, weight and type of cancer. Everyone should know the signs of a clot: a swollen, painful leg or sudden breathlessness or chest pain.

## Summary

Routine thromboprophylaxis is not recommended for all outpatients with cancer (ITAC 2022; ASCO 2020; NICE NG89 for mobile people on anticancer treatment). Risk is assessed at the start of systemic treatment and periodically, with a validated model: the Khorana score gives 2 points for a very high-risk cancer site and 1 point each for a high-risk site, platelets of 350 × 10⁹/L or more, haemoglobin below 100 g/L or use of an erythropoiesis-stimulating agent, white cells above 11 × 10⁹/L and a body mass index of 35 or more.

The guidelines differ on who should be offered prophylaxis. ITAC (2022) recommends rivaroxaban or apixaban for ambulatory patients on systemic anticancer therapy with a Khorana score of 2 or more who are not bleeding or at high bleeding risk (grade 1B); ASCO (2020) says clinicians may offer apixaban, rivaroxaban or low-molecular-weight heparin to selected high-risk outpatients. NICE NG89 (2018) does not use a score: it advises against prophylaxis for mobile people on cancer treatment except for myeloma on thalidomide, pomalidomide or lenalidomide with steroids (aspirin or low-molecular-weight heparin) and pancreatic cancer on chemotherapy (low-molecular-weight heparin), continued for as long as chemotherapy lasts. ITAC also recommends prophylaxis in locally advanced or metastatic pancreatic cancer with low bleeding risk (low-molecular-weight heparin grade 1A, rivaroxaban or apixaban grade 1B) and in myeloma on immunomodulatory drugs (grade 1A), and does not recommend low-molecular-weight heparin prophylaxis outside a trial in advanced lung cancer.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: Khorana score; ambulatory thromboprophylaxis; primary VTE prophylaxis in cancer outpatients; cancer-associated thrombosis prevention; blood thinners to prevent clots during chemotherapy
- Tags: protocol; thrombosis; supportive-care

## Connected records

- drugs: [Aspirin](https://onco.cc/drugs/aspirin/), [Lenalidomide](https://onco.cc/drugs/lenalidomide/), [Pomalidomide](https://onco.cc/drugs/pomalidomide/), [Thalidomide](https://onco.cc/drugs/thalidomide/)
- cancers: [Multiple myeloma](https://onco.cc/cancers/multiple-myeloma/), [Pancreatic ductal adenocarcinoma](https://onco.cc/cancers/pancreatic/)
- fronts: [Supportive Care & Survivorship](https://onco.cc/fronts/supportive-care/)
- technologies: [Cancer-associated thrombosis prevention and treatment](https://onco.cc/technologies/cancer-associated-thrombosis/)
- institutions: [American Society of Clinical Oncology (ASCO)](https://onco.cc/institutions/asco/), [European Society for Medical Oncology (ESMO)](https://onco.cc/institutions/esmo/), [National Institute for Health and Care Excellence](https://onco.cc/institutions/nice/)
- terms: [Venous thromboembolism (VTE)](https://onco.cc/terms/vte/)
- ideas: [A blood clot risk score at the start of chemotherapy, with preventive anticoagulation offered to those at higher risk](https://onco.cc/ideas/idea-upgrade-clot-risk-score-and-preventive-anticoagulation/)

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