The short answer
A fever that has no clear cause and keeps returning can be a sign of some cancers, especially blood cancers like leukemia and lymphoma. Most fevers come from infections, but a persistent, unexplained fever should be checked.
A persistent or recurring fever with no clear cause can be a warning sign of some cancers.
It is more often linked to blood cancers such as leukemia and lymphoma.
Most fevers are caused by infections, not cancer.
A fever that keeps returning or has no clear cause should be evaluated.
Choose how you want to read this
The whole article, with every detail and caution.
This page is for anyone with a fever that keeps coming back or has no clear cause. It explains how cancer can cause fever, why infection is still the most likely cause, and when to get care now.
The simple version
Fevers are the body's normal response to fighting an infection. MedlinePlus says an adult probably has a fever when the temperature measured in the mouth is above 99°F to 99.5°F (37.2°C to 37.5°C). Most fevers pass within a few days. They have nothing to do with cancer. A fever that keeps coming back, lasts a long time, or has no clear cause is different. That pattern is worth checking.
Which cancers cause fever
Fever with no obvious cause is most often linked to blood cancers. These include leukemia, a cancer of the blood and bone marrow, and lymphoma, a cancer of the lymph system. In lymphoma, doctors group fever with two other symptoms: drenching night sweats, and weight loss you did not try to lose. Doctors call this trio "B symptoms." A tumor itself can cause fever, but in people with cancer, infection is still the most common cause.
Infection is still the most likely cause
Most fevers, even ones that come back, are from infections. Colds and urinary tract infections are common examples. A doctor's first job is to rule out these more common explanations.
What a workup typically involves
Your doctor asks about the fever's pattern. How high does it get? How long does it last? Does it respond to fever-reducing medicine? A physical exam checks for swollen lymph nodes, an enlarged spleen, or a rash. Blood tests, including a complete blood count, look for signs of infection or abnormal blood cell counts. Abnormal counts can point toward leukemia. If those results are unclear, doctors may order imaging, such as a CT scan, to look for swollen lymph nodes or masses elsewhere in the body. If a swollen node or a mass is found, a biopsy usually follows. That means removing a small piece of tissue to examine under a microscope. NCI says the pathologist usually sends the report to the doctor within 10 days after the biopsy.
Doctors also look for a hidden infection before considering cancer. That can mean a urine test, a chest x-ray, or blood cultures, which check whether bacteria are growing in your bloodstream. Infections are a more common cause of fever than cancer.
What a normal test does not rule out
A single round of normal blood tests does not rule out everything. If your fever keeps returning after an initial workup is normal, that is a reason to follow up. It is not a reason to stop looking.
Tracking helps your visit
Keep a simple log: the date, the highest temperature, how long it lasted, and any other symptoms like night sweats, weight loss, or fatigue. Note any recent travel, sick contacts, or new medicines. This record helps your doctor tell a true unexplained fever apart from a string of ordinary colds.
When to get care now
See a doctor promptly for a fever above 100.4°F (38°C) that will not go away, or one that keeps returning over several weeks. Get care sooner if it comes with drenching night sweats, unexplained weight loss, or swollen lymph nodes.
If you are having chemotherapy now, a fever is handled differently. CDC says a fever during chemotherapy is a medical emergency, because chemotherapy can leave you with too few white cells to contain an infection. It tells you to call your doctor immediately at a temperature of 100.4°F (38°C) or higher. Keep that number, including the out-of-hours one, where you can reach it. CDC adds that if you do go to the emergency room, tell the person checking you in that you are a cancer patient having chemotherapy.
Also get emergency care (call 911 or go to an emergency department) for a fever with shaking chills, confusion, a fast heartbeat, breathlessness, or a rash that does not fade when pressed. Those can be signs of sepsis.
What to ask your doctor
- Could my recurring fever be from an infection or something else?
- Should my blood counts and lymph nodes be checked?
- What tests would help find the cause?
- What other symptoms should I watch for?
Sources
Common questions
When is a fever a concern?
Most fevers come from infections and pass quickly. A fever that keeps returning, lasts a long time, or has no clear cause is worth checking, especially with other symptoms.
Which cancers cause fever?
Fever is more often linked to blood cancers such as leukemia and lymphoma. Tumors themselves can also cause fever, though infection is a more common cause.
Why does cancer cause fever?
A tumor itself can cause fever. In people with cancer, though, infection is the most common cause of fever.
When should I see a doctor?
See a doctor for a fever that keeps returning, lasts more than a few days, or has no clear cause, especially with night sweats, weight loss, or swollen lymph nodes.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Talk with a trained specialist or navigator
Cancer Explained provides educational guidance, but does not replace trained specialists, social workers, or your medical team.
Talk to a trained cancer information specialist
Free, confidential assistance from NCI Cancer Information Service via phone, chat, or email.
Contact your oncology team
Locate after-hours contact numbers, portal messages, or urgent triage phone lines.
Find a patient navigator
Get one-on-one help with appointments, logistics, translation, and care coordination.
Find a genetic counselor
Discuss inherited mutation risk, family history, and genetic testing options.
Find an oncology social worker
Access emotional counseling, family support groups, and mental health resources.
Find a financial navigator
Locate copay assistance foundations, grant programs, and lodging/travel support.
Find a clinical-trial specialist
Search matching studies and speak with NCI trial information specialists.
Get urgent help
Fever of 100.4°F (38°C) or higher during chemo, severe pain, or trouble breathing: call your cancer care team right away, day or night. Call 911 for an emergency.
Know someone who needs this?
Plenty of people are looking for something like this and do not know where to start. If this would help a friend or someone you love, send it on — we have written an opening line so you do not have to stare at an empty message. You can change every word of it.
Your message is written and sent in your own email or messaging app — we never see who you send it to, and nothing is added to any list.
Plain-language explanation of the published sources cited on this page. AI-assisted, source-checked, not clinician-reviewed.
Last updated: 2026-09-29Next planned review: 2027-07-07
Review details and limits
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status — Source checked. This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
High-risk topic — talk to your care team. This topic can involve urgent, individual medical decisions. This page is general education only: it cannot tell you whether your situation is an emergency or what you personally should do. Follow your oncology team's instructions and contact them for individual guidance.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Words to know
Tap any term to see what it means.
Knowledge check
0 of 3 answered
This self-assessment checks understanding of educational content only. It is not medical advice.
How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
Read more about our editorial process, our use of AI, and our corrections policy.
Spotted a problem? Report an error — a factual mistake, broken or outdated source, confusing wording, or anything that seems unsafe. Please do not include names, medical record numbers, dates of birth, addresses, or other identifying medical information in your report.
After using this page, do you understand what to do next?
Anonymous — we only record the answer, never who gave it.