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.
Fever can also appear when a cancer has spread.
Most fevers are caused by infections, not cancer.
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The full explanation.
The simple version
Fevers are the body's normal response to fighting an infection. A temperature above about 100.4°F (38°C) counts as a fever for most adults. 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." Cancer can cause fever in more than one way. Some tumors release chemicals called cytokines that raise body temperature directly. Blood cancers can crowd out normal white blood cells in the bone marrow. That weakens your defenses against ordinary infections, which can trigger repeated fevers. Fever can also appear once a cancer has spread to the liver or elsewhere in the body.
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. Some infections, like mononucleosis, cause fevers that last for weeks on their own. 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. These tests are quick, and most people who go through this workup end up with an infection as the answer, not a blood cancer.
What a normal test does not rule out
A single round of normal blood tests does not rule out everything. This is especially true early in a slow-growing lymphoma, which can take time to show up on a blood count. 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, and 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 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
Words to know
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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. It can also occur with other cancers, especially if they have spread.
Why does cancer cause fever?
Some cancers affect the immune system or produce substances that raise body temperature. Blood cancers can also make it harder to fight infections, which cause fevers.
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
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Last updated: 2026-08-18Next planned review: 2027-07-07
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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. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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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. We do not employ clinicians and do not intend to — our work 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 checked line by line against the sources listed on it. That confirms the sources support what the page says. 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.
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