The Role Eosinophils Play in Cancer

Eosinophils are a type of white blood cell produced in the bone marrow that makes up about 5 percent of the total number of white blood cells. Eosinophils can circulate in the blood and also are found outside blood vessels in other organs in the body. The gastrointestinal (GI) tract typically has the highest number of eosinophils relative to other organs.

The Function of Eosinophils

Eosinophils protect the body by killing bacteria and parasites, but can cause problems when they react incorrectly and cause allergies and other inflammatory reactions in the body. For example, food allergies can cause too many eosinophils to gather in the digestive tract, which may lead to symptoms such as diarrhea and damage to the cells lining the GI tract.

Eosinophils are part of the innate immune system, which means that they can "non-specifically" destroy any invaders they encounter in the body, such as bacteria and parasites. Eosinophils do not have to recognize the invader specifically, but instead simply recognize the invader as something that is foreign to the body and should not be present.

When There Are Too Many Eosinophils

When a large number of eosinophils are dispatched to a certain site in the body, or when the bone marrow produces too many eosinophils, a condition known as eosinophilia exists. Eosinophilia can result from a variety of conditions, diseases, and factors, including:

• Parasitic and fungal diseases
• Allergies
• Adrenal conditions
• Skin disorders
• Toxins
• Autoimmune diseases
• Endocrine disorders

In addition, eosinophilia can develop in response to certain cancers, including:

• Lymphoma (Hodgkin's and non-Hodgkin's lymphoma)
• Leukemia (chronic myeloid leukemia, adult T-cell leukemia/lymphoma, eosinophilic leukemia)
• Colorectal cancer
• Lung cancer

Eosinophils and Colorectal Cancer

The number of eosinophils in the blood can rise during a normal response to allergic reactions, fungal and parasitic infections, medications, and some types of cancer.

A study published in the journal Modern Pathology in 2014 looked at how eosinophils might predict outcomes for patients with colorectal cancer. Although staging of colorectal cancer typically is based on information about the tumor itself, lymph node involvement, and the presence of metastases (cancer spread to other sites), often two patients with the same staging will have dramatically different outcomes.

The study's authors examined whether eosinophil levels in or around a colorectal tumor helped predict outcome. They concluded that higher numbers of eosinophils around the primary colorectal tumor were associated with an improved patient outcome and, as a result, that eosinophils should be routinely counted during tumor examination.