Cancer and Pulmonary Embolism: Risks, Symptoms, Prevention, and Treatment

Cancer changes how blood behaves. It makes clots more likely, and when a clot breaks off and blocks an artery in the lungs, things can go wrong fast. That blockage-called a pulmonary embolism-is one of the main non-cancer causes of death in people with cancer. The good news? Knowing the signs, acting quickly, and choosing the right prevention and treatment plan can dramatically cut the risk of harm.

If you came here after a scare-leg swelling, sudden breathlessness, a tight chest-you want straight answers. This is a clear, practical guide built for patients and families. I’ll explain the link between cancer and clots, the symptoms you should never ignore, how doctors confirm a PE, and what treatment looks like on the NHS and beyond. I’ll also give you checklists and questions you can take to your next appointment. I’m UK-based, so I’ll reference NICE guidance and NHS pathways, but the core advice applies widely.

TL;DR: Key takeaways

• Cancer makes blood “stickier.” PE risk is highest around diagnosis, during chemotherapy, after major surgery, and with limited mobility.
• Red flags: sudden breathlessness, chest pain that worsens with deep breaths, coughing blood, or fainting. Call emergency services if these appear.
• Diagnosis relies on a CT pulmonary angiogram (CTPA). D-dimer is less helpful in cancer; doctors often go straight to imaging when suspicion is high.
• Treatment is anticoagulation (blood thinners). Apixaban and LMWH are common choices; type depends on cancer site and bleeding risk. Duration is usually at least 3-6 months and longer if cancer is active.
• Prevention is targeted: extended anti-clot injections after major cancer surgery, and preventive tablets/injections in high‑risk outpatients on chemotherapy when bleeding risk is low.

The link between cancer and PE: why it happens and who’s most at risk

Clotting is part of our immune toolkit. Cancer hijacks that system. Tumours release substances that trigger clot formation; treatments like chemotherapy can injure blood vessel linings; and reduced movement adds another nudge. Put those together, and clots form more easily in the deep veins (usually the legs). If a piece travels to the lungs, you get a PE.

Risk is not the same for everyone. It changes with cancer type, stage, treatment, and personal factors (age, prior clots, obesity, infection, hospital stays, and central venous catheters). The first 3-6 months after a cancer diagnosis are the riskiest. Abdominal and pelvic surgery raise risk for weeks. Certain cancers-like pancreatic, gastric, brain, lung, ovarian, and myeloma-carry a particularly high clot risk. Blood cancers (lymphoma, leukemia) also raise risk, especially with specific drug regimens.

How high is the risk? In simple terms: cancer multiplies the chance of a dangerous clot by several times compared with people without cancer. Studies consistently show it’s one of the leading causes of non‑cancer death in cancer patients. That’s why guidelines from NICE (UK), ASCO (US), and ASH strongly focus on early recognition and targeted prevention.

Doctors sometimes use the Khorana Score to estimate clot risk in people starting chemotherapy. It uses five pieces of information: cancer site, platelet count, haemoglobin/ESA use, white cell count, and BMI. A score of 2 or more means higher risk and is where preventive blood thinners may be considered if the bleeding risk is acceptable.

These numbers are broad ranges from large cohort analyses; individual risk varies. Your oncologist will weigh your personal clot and bleeding risks before recommending prevention or treatment.

Guidelines behind these approaches include NICE NG158 (diagnosis and management of VTE, updated 2023), NICE NG89 (VTE prophylaxis in hospital), ASCO’s 2023 cancer-associated thrombosis update, ASH 2021 VTE guidelines, and the European Society of Cardiology’s guidance on acute PE.

Spotting symptoms and knowing when to act

PE can be sneaky or dramatic. Either way, time matters. Here’s what to watch for, and what to do.

Common PE symptoms:

• Sudden breathlessness (at rest or with mild effort)
• Sharp chest pain that worsens when you breathe in
• Coughing blood (even small amounts)
• Fast heartbeat, light-headedness, or fainting
• Unexplained low oxygen levels picked up during a clinic visit

Common DVT symptoms (the usual source of a PE):

• One‑sided leg swelling (calf or thigh)
• Leg pain, warmth, redness, or a heavy, tight feeling
• Visible swollen veins or a change in skin colour

When to seek urgent help in the UK:

• Call emergency services if you have sudden, unexplained breathlessness, chest pain, fainting, or coughing blood.
• If symptoms are milder but concerning (new leg swelling, dull chest ache), ring NHS 111 or contact your oncology team urgently for the same-day plan.

People on chemotherapy, with recent surgery, or with a central line should keep a lower threshold for getting checked. It’s always okay to be told it’s nothing rather than miss a PE.

What symptoms are often misread?

• “It’s just anxiety.” Anxiety can cause chest tightness, but it doesn’t cause low oxygen, leg swelling, or coughing blood.
• “It’s my chest infection.” Infections and PE can overlap. If antibiotics aren’t helping, push for reassessment.
• “It’s my chemo fatigue.” Fatigue is common, but sudden breathlessness or a painful, swollen calf is not typical “just chemo.”

How PE is diagnosed in cancer: tests, trade‑offs, and speed

The standard test for PE is a CT pulmonary angiogram (CTPA). It takes minutes, shows clots clearly, and guides treatment. If you can’t have contrast dye (because of severe kidney issues or allergies), doctors may use a ventilation/perfusion scan (V/Q scan), which compares airflow and blood flow in the lungs.

Do blood tests help? D‑dimer is a clot breakdown product. In cancer, D‑dimer is often elevated even without a clot, which makes it less useful for ruling out PE. That’s why many clinicians go straight to imaging when the story fits. Oxygen saturation, troponin, and BNP can suggest strain on the heart but don’t confirm a PE on their own.

What about the legs? If PE is suspected but the chest scan isn’t immediately available, a leg ultrasound (Doppler) can look for DVT. Finding a fresh DVT in the right clinical setting can be enough to start treatment while arranging a chest scan.

Risk stratification right after diagnosis matters. If the clot is large or the heart is struggling (shown by imaging and blood tests), the team might consider more intensive measures. Most cancer patients with PE will be treated with anticoagulants alone, but a tiny minority with life‑threatening, unstable PE may need thrombolysis (clot‑busting) or catheter procedures. Because cancer can raise bleeding risk, these invasive options are reserved for specific emergencies and handled by specialist teams.

UK pathway tip: NICE NG158 supports using clinical probability tools and imaging promptly. If you’re hemodynamically unstable, it’s straight to emergency care. Stable but suspicious? Expect same‑day imaging where possible.

Treatment: anticoagulants, duration, procedures, and what to expect

The backbone of PE treatment is anticoagulation-medicines that stop the clot from growing while your body slowly dissolves it. This is not about “thinning blood” in a literal sense; it’s about tipping the balance away from clotting.

Common options in cancer:

• Direct oral anticoagulants (DOACs): apixaban, rivaroxaban, edoxaban. Pros: tablets, no routine blood tests. Cons: drug‑drug interactions, higher bleeding risk with some GI and GU cancers, may be less suitable after certain gut surgeries or if swallowing is difficult.
• Low molecular weight heparin (LMWH): enoxaparin, dalteparin. Pros: proven in cancer, fewer drug interactions. Cons: daily injections, bruising at the injection site, cost/logistics.
• Warfarin: rarely first‑line now in cancer due to interactions and fluctuating levels; still used if other options don’t fit and monitoring is feasible.

What do guidelines say? ASCO’s 2023 update supports DOACs (especially apixaban) or LMWH for treatment of cancer‑associated PE, with careful attention to bleeding risk in GI/GU cancers. ASH 2021 and NICE NG158 echo this: pick the agent that balances clot control, bleeding risk, practicality, and interactions.

How long is treatment? Most people need at least 3-6 months. If the cancer is active, treatment continues beyond 6 months, reassessed regularly. If the cancer is in remission and your risk is now low, your team may consider stopping after that initial period. Recurrence risk is higher in cancer, so don’t stop early without a plan.

When is an IVC filter used? If you absolutely cannot take anticoagulants (for example, you’re bleeding or you’ve just had neurosurgery), a temporary inferior vena cava (IVC) filter may be placed to catch clots traveling from the legs. Once it’s safe to start blood thinners, filters are usually removed to avoid long‑term complications.

Thrombolysis and catheter‑directed therapy are reserved for massive or high‑risk PE with shock or severe right‑heart strain. In cancer patients, the threshold is carefully weighed because bleeding can be catastrophic. These decisions are made by multidisciplinary teams.

Chemo, surgery, and anticoagulants-how do they mix?

• Chemotherapy: Some regimens interact with DOACs (through CYP3A4/P‑gp). Your pharmacist will check. If interactions are strong, LMWH may be safer.
• Radiotherapy: Usually fine with anticoagulation; watch for mucosal bleeding if irradiating GI/GU tracts.
• Surgery/biopsies: Anticoagulants are paused with a bridging plan. Tell every surgeon and dentist you’re on them.
• Central lines: Anticoagulation does not mean you can’t have a line placed; teams coordinate timing to reduce bleeding risk.

Side effects and what to watch:

• Easy bruising, nosebleeds, gum bleeding, or heavier periods (if applicable)
• Black or tarry stools, vomiting blood, or coughing blood-seek urgent care
• Severe headache or neurological symptoms-urgent assessment for intracranial bleed
• New breathlessness or chest pain despite treatment-rule out progression or recurrence

Practical tips that help:

• Take DOACs at the same time daily; don’t double up if you miss a dose-check the leaflet or ring your team for advice.
• Keep a medication list on your phone. Include supplements-some, like St John’s Wort, interact.
• Stay moving as you’re able. Even calf pumps in a chair help if you’re wiped out from chemo.
• Hydrate, especially during long clinic days and travel.
• Use compression stockings only if recommended after an ultrasound confirms DVT and your clinician advises them.

Evidence notes: The shift from LMWH‑only to including DOACs is based on randomized trials showing similar clot prevention with differing bleeding profiles, particularly in GI cancers. That’s why your cancer type matters so much in the decision.

Prevention, checklists, FAQs, and next steps

Prevention is targeted-used where it clearly helps more than it harms. Not every cancer patient needs a preventive anticoagulant, and blanket treatment would cause avoidable bleeding.

Who should usually get preventive treatment?

• After major abdominal or pelvic cancer surgery: extended LMWH for up to 28 days is standard in guidelines like NICE NG89.
• Hospital inpatients with reduced mobility: mechanical devices and pharmacologic prophylaxis unless bleeding risk is high.
• High‑risk outpatients on chemotherapy (high Khorana score, high‑risk cancer types): ASCO 2023 supports apixaban 2.5 mg twice daily or rivaroxaban 10 mg daily if bleeding risk is low and interactions are manageable.
• Myeloma on IMiDs (lenalidomide, thalidomide): prophylaxis varies by risk-sometimes aspirin, sometimes anticoagulants.

Who might not be a good candidate for preventive anticoagulants?

• Active bleeding or very high bleeding risk (brain tumours, recent brain surgery, uncontrolled ulcers)
• Severe thrombocytopenia (low platelets)
• Strong drug interactions that can’t be safely managed
• Major upcoming procedures

Home prevention habits that actually help:

• Move every hour when awake. During treatment days, do ankle circles and calf raises while seated.
• Drink water regularly; dehydration thickens blood.
• Know your personal risk windows: new chemo cycles, just after surgery, infections, long car rides.
• Plan travel. For flights or long drives >4 hours: aisle seat if possible, walk the aisle every hour, calf exercises, consider graduated compression if advised, and keep hydrated. If you’ve had a PE within the last few weeks, ask your team before flying.

Checklist: what to tell your team if you’re worried about a clot

• Exact symptoms and when they started (e.g., sudden sharp chest pain while walking to the kitchen at 10 am)
• Recent changes: new chemo cycle, infection, surgery, catheter placement
• Current medicines, including over‑the‑counter pills and supplements
• Any bleeding issues (nosebleeds, black stools, heavy periods)
• Relevant history: prior clots, miscarriages, family history of clots

Decision hints you can use with your clinician

• If GI or GU cancer with bleeding risk → LMWH often safer than certain DOACs.
• If many drug interactions or gut absorption problems → LMWH beats DOACs.
• If tablets are key for quality of life and bleeding risk is low → apixaban commonly chosen.
• Active cancer or ongoing treatment → expect anticoagulation beyond 6 months, with regular reviews.

Mini‑FAQ

• Is PE common in cancer? Yes. Cancer accounts for a large share of VTE events. It’s a leading non‑cancer cause of death in this group; that’s why teams take it so seriously.
• Which cancers carry the highest PE risk? Pancreatic and gastric are near the top, followed by brain, lung, ovarian, myeloma, and some blood cancers. Risk is highest early after diagnosis and during treatment.
• Can immunotherapy cause clots? Immunotherapy can be linked with VTE, but the relationship varies by regimen and patient factors. Your team watches for it, especially when other risks pile up (e.g., infections, immobility).
• I had an unprovoked PE. Should I be screened for hidden cancer? In people without known cancer, age‑appropriate cancer screening and a basic evaluation are recommended; routine extensive scans find few cancers and aren’t generally advised by NICE unless red flags are present.
• Can I keep having chemo if I’ve had a PE? Often, yes-with anticoagulation. Timing, interactions, and bleeding risks are managed by your oncology and haematology teams together.
• Can I travel? If you’re stable on treatment, many people can fly after a few weeks. Get the go‑ahead from your team, plan movement and hydration, and carry your medicines in your hand luggage.
• Do compression stockings prevent PE? They can help with DVT symptoms and prevention in some cases, especially after surgery or hospital stays, but they’re not a substitute for anticoagulation when that’s indicated.
• When can I stop anticoagulation? Typically after at least 3-6 months and when cancer is no longer active or you’re off treatment; your team will weigh recurrence risk vs bleeding risk.

Next steps by scenario

• You’re on chemotherapy and notice new leg swelling: Call your oncology team the same day. Ask for an urgent leg ultrasound and guidance on starting anticoagulation if DVT is confirmed.
• You’ve had recent major cancer surgery and are short of breath: Treat this as an emergency. Tell the call handler about the surgery and concern for PE.
• You have a GI cancer and were offered a DOAC: Ask about bleeding risk vs LMWH and whether your specific tumour location makes injections safer initially.
• You’re struggling with daily LMWH injections: Speak up. Apixaban may be an option if bleeding risk and interactions are acceptable.
• You’re planning a long‑haul flight: Ask your team about timing relative to your PE and treatment, whether extra precautions or temporary dose adjustments are needed, and bring a fit‑to‑fly letter if advised.

When to call for urgent help (keep this handy):

• Sudden, unexplained breathlessness, chest pain, fainting, or coughing blood
• Black stools, vomiting blood, severe headaches, or stroke‑like symptoms while on anticoagulants
• Rapidly worsening leg swelling and pain, especially if accompanied by breathlessness

Guideline anchors for decision‑making: NICE NG158 (VTE diagnosis/management), NICE NG89 (hospital VTE prevention), ASCO 2023 guideline update on cancer‑associated thrombosis, ASH 2021 VTE guidelines, and ESC guidance on acute PE. These are what UK and international teams use to balance clot prevention, bleeding risk, and quality of life in 2025.

You don’t have to memorise any of this. Save this page, bring the checklists to clinic, and ask your team to talk you through your personal plan. The aim isn’t to turn you into a doctor-it’s to help you spot problems early and make good, shared decisions that fit your cancer, your life, and your goals.