Eosinophil Levels and Cancer
Published on:
July 23, 2026
Eosinophils are white blood cells that play a key role in how the immune system responds to infections, allergies, and some serious illnesses. High levels usually mean the body is reacting to something. However, high eosinophils are rarely caused by cancer
Still, if a blood test shows an elevated eosinophil count, you’ll probably have questions about what that means for your overall health
“The vast majority of high eosinophil counts are related to an infection or autoimmune condition, not to cancer,” said Matthew J. Pianko, MD, an American Society of Clinical Oncology (ASCO) expert and a hematologist-oncologist at the University of Michigan Medical School
What are eosinophils?
The body makes many different types of white blood cells (also called leukocytes). Like other white blood cells, eosinophils have a specific job. Their main role is to recognize and get rid of certain infections, especially parasites. They are also involved in helping the immune system respond to inflammation and allergic reactions
Eosinophils are measured by a common blood test called a complete blood count (CBC) with differential. Your doctor may order this routine blood test as part of a checkup or to help figure out a particular health problem
Eosinophils usually make up 5% or less of your overall white blood cells. Normal eosinophil ranges can vary based on the lab used to run the test. Eosinophil counts are usually reported in 2 ways:
- As an absolute eosinophil count (AEC), or the number of eosinophils found in 1 microliter of blood. Doctors consider this the most accurate count. An absolute eosinophil count below 500 cells/microliter of blood (<500/μL) is considered in the normal range.
- As a percentage of your overall white blood cell count. This is a less reliable way to find out the actual number of eosinophils because the overall count can vary from person to person and with each blood draw.
“You should pay attention to both results, but the absolute eosinophil count is most important. Your doctor can help you interpret your blood test results and whether your eosinophil levels are actually high,” Dr. Pianko said
What can cause high eosinophil levels?
A higher-than-normal eosinophil level is called eosinophilia. It can be caused by:
- Allergies to food or specific substances or chemicals in the environment
- Worm-type parasite infections, although these are uncommon in the United States
- Conditions affecting parts of the gastrointestinal tract, including the esophagus, stomach, intestines, and bladder
- Lung disorders, including asthma, bronchitis, and pneumonia
- Certain blood and tissue disorders
- Skin conditions, such as eczema
- Autoimmune conditions, such as Crohn’s disease
- Reactions to certain medications
- Certain cancers, but this is rare
“With these conditions, the body releases chemical messengers called cytokines. The cytokines tell the immune system to fight back by producing more eosinophils,” Dr. Pianko said
Having eosinophilia on its own is not enough to diagnose any specific condition. If your eosinophil levels are high, your doctor will check for symptoms and order more tests to find out the cause. For example, additional blood tests can help diagnose certain infections or allergies. Stool tests can help find parasites or conditions in the digestive tract. An imaging test can help find problems that may or may not be serious, such as cancer
If left untreated, eosinophilia can damage your organs over time. The right treatment depends on what’s causing eosinophilia. Once that condition is treated, eosinophil levels usually go back to normal
Do high levels of eosinophils suggest cancer?
Most of the time, high eosinophil levels are due to something other than cancer. But your doctor may consider cancer if:
- More common causes of eosinophilia have been ruled out.
- Eosinophilia continues after treatment for another condition.
- You have other signs and symptoms of cancer.
“A doctor might check for cancer if someone has eosinophilia along with low white blood cells, low hemoglobin, low platelets, swollen lymph nodes, or enlarged organs,” said Dr. Pianko
High eosinophil levels are associated with blood cancers, such as leukemia and lymphoma. These cancers often start in the bone marrow. Since all blood cells begin as stem cells in the bone marrow, these cancers can cause eosinophils to grow out of control
Less commonly, high eosinophil levels have been found in people with breast, cervical, colorectal, kidney, lung, ovarian, prostate, and melanoma cancers. Experts believe this happens when these types of solid tumors produce cytokines that cause increased eosinophil growth
“Cases in which a high eosinophil count is caused by a blood cancer or solid tumor are thankfully quite rare. But they’re important to keep in mind,” Dr. Pianko said
What are the signs and symptoms of high eosinophils?
On its own, a high eosinophil level is considered one of many possible signs or symptoms of an underlying health problem. Common symptoms related to conditions that cause eosinophilia include fatigue, rash, shortness of breath, and swelling
When should you talk to your doctor about eosinophil levels?
Talk with your doctor if you have persistent, unexplained eosinophilia. Ask questions like:
- What do my eosinophil counts (absolute and percentage) mean?
- What other tests do you recommend for me?
- Should I see a hematologist (a doctor who specializes in blood disorders) for further evaluation?
“Most concerns about eosinophil levels can be explained, but it’s always good to ask questions,” Dr. Pianko said. “Your healthcare provider can help answer your questions and identify if you have an undiagnosed problem that needs treatment, whether it’s cancer or not.”
Learn more from the American Cancer Society:
- Blood Cells and Bone Marrow
- Signs and Symptoms of Cancer
Dr. Pianko is a member of ASCO’sPatient Information Advisory Committee
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