Yet fever symptoms are associated with specific types of cancer, leukemia and lymphoma among them. What healthcare providers refer to as a “fever of unknown origin” (FUO) is just one clue toward a diagnosis and treatment.
This article defines what FUO is and some of its possible causes. It details why fever can be an early symptom of leukemia and other cancers.
Fever of Unknown Origin
“Fever of unknown origin” is the term used to describe a fever that meets all of the following criteria:
Temperature of 101 degrees F or more Lasts for at least three weeks, either constantly or with multiple episodes Does not occur in an immunocompromised person, such as with HIV infection Has no other identifiable cause, after a physical exam and multiple lab and imaging tests
Keep in mind that an FUO has to be prolonged, so that generally rules out the flu, a routine cold, or many of the other common causes of fever that would be expected to resolve within three weeks.
Possible Causes of FUO
Given that there are hundreds of possible causes of FUO, the list of possible diagnoses—even for fevers lasting longer than three weeks—is quite long. Many of these causes fall into one of three categories: infection, cancer and other diseases, or medication.
Infections That Cause Fever
Many types of infections can lead to fever of unexplained origin. It’s common for nausea, fatigue, and other symptoms to arise with the fever, depending on the cause. Conditions may include:
Ear infections Urinary tract infections (UTIs) Gastroenteritis (stomach flu) Pneumonia
Fever associated with an infection remains the leading cause of FUO.
Cancers That Cause Fever
Several different types of cancer may include FUO as a symptom. These cancers include:
Lymphomas, both Hodgkin and non-Hodgkin lymphoma types Leukemias, notably acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CLL) Renal cell (kidney) cancers Hepatocellular (liver) carcinoma Castleman’s disease Glioblastoma multiforme, an aggressive brain cancer Ovarian cancer Colorectal cancer
However, a number of other health conditions may begin with infection and/or inflammation. They also may include FUO as a symptom. Among these conditions are:
Appendicitis Atrial myxoma, a benign tumor in the heart Deep vein thrombosis Meningitis Mononucleosis (mono) Autoimmune diseases, like arthritis, lupus, and multiple sclerosis (MS) Tuberculosis
Medications That Cause Fever
Sometimes drugs may be to blame, including certain antibiotics and medications that are taken to prevent seizures. Drugs that can lead to FUO include sulfa-based products, such as stool softeners, and even pain medications like nonsteroidal anti-inflammatory drugs (NSAIDs).
These “drug fevers” are more common if you have taken a drug for years, and less so when it is a new medication. In most cases, the fever goes away within 72 hours if you stop taking the drug.
Why Blood Cancers Cause Fevers
Two kinds of blood cancer, leukemia and lymphoma, are known to produce fevers as an early sign.
For example, about 25% of people with Hodgkin’s lymphoma may have what are called “B symptoms.” These include fevers, unintentional weight loss, and drenching night sweats. These symptoms suggest a more aggressive and rapidly growing cancer.
When blood cancers do cause fevers, those fevers can, in some cases, impact the stage and prognosis (or outlook) of the illness.
Summary
There are more than 200 possible causes for why you may experience a fever of unexplained origin, and in most cases, the FUO is not caused by cancer. It’s far more likely that fever is caused by the flu or another uncomplicated infection. Once the infection has resolved, the fever will go away too.
That said, fever is a common symptom in some types of cancer, including leukemia and lymphoma. These cancers of the blood are known to cause a fever in their early stages.
If you have an unexplained fever, be sure to work closely with a healthcare provider to rule out the more obvious causes, such as an adverse drug reaction. It’s important to give a precise medical history and tell them about any other signs or symptoms that arise.
A Word From Verywell
Most FUOs will resolve on their own once the underlying cause is addressed. That said, don’t ignore an unexplained fever, especially one that recurs. It may be an important clue about a serious health issue.
