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.

Eosinophils protect the body 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 that they encounter in the body, such as bacteria and parasites. Non-specifically means that eosinophils do not have to recognize the invader specifically, but instead simply recognize the invader as something that should not be present and should be destroyed.

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 (ATLL), eosinophilic leukemia)
• Colorectal cancer
• Lung 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 2011 study published in the Journal of Clinical Oncology examined the relationship between eosinophils in peripheral blood and the incidence of colorectal cancer. The researchers found that a higher number of peripheral blood eosinophils was associated with a reduced risk of dying from colorectal cancer, especially in patients who never smoked and in males. Although the study could not identify the mechanism to explain this relationship, one plausible theory is that a more active immune system reduces the risk of developing colorectal cancer.

Another 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.

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