Neutrophils are a type of white blood cell that play a role in the body’s immune system. Elevated levels, known as neutrophilia, often indicate infection or inflammation. High neutrophil counts can also be observed in the context of cancer, providing insights into the disease and patient outcomes.
What Are Neutrophils?
Neutrophils are the most abundant type of white blood cell, making up 55% to 70% of all white blood cells. Produced in the bone marrow, they circulate throughout the blood, tissues, and lymph nodes. Neutrophils are a fundamental part of the innate immune system, serving as the body’s first responders to infection and injury.
These cells combat infections by trapping and ingesting bacteria, viruses, and fungi through phagocytosis. They also release antimicrobial peptides and enzymes, and can form web-like structures called neutrophil extracellular traps (NETs) to ensnare pathogens. This rapid response helps neutralize threats.
Understanding Elevated Neutrophil Counts
An elevated neutrophil count, or neutrophilia, indicates an increased number of these white blood cells in the bloodstream. Normal levels range from 2,500 to 7,000 neutrophils per microliter of blood, with counts over 7,700 generally considered high.
Neutrophilia commonly arises from the body’s response to infections, especially bacterial infections, as the bone marrow increases neutrophil production. Inflammatory conditions like rheumatoid arthritis or inflammatory bowel disease can also lead to sustained neutrophilia. Physical or emotional stress, vigorous exercise, tissue damage, and certain medications like corticosteroids can temporarily elevate neutrophil levels. An elevated neutrophil count can also signal an underlying malignancy, including various forms of cancer.
How Neutrophils Influence Cancer Progression
Neutrophils can influence cancer development. They promote tumor growth by releasing soluble factors and proteases. They also contribute to angiogenesis, the formation of new blood vessels that supply tumors with nutrients and oxygen, by producing pro-angiogenic factors. This helps tumors grow larger and faster.
Neutrophils also play a role in metastasis, the spread of cancer cells from the primary tumor to distant sites. They can act as carriers for tumor cells, induce changes that promote invasiveness, and help establish pre-metastatic niches where cancer cells can settle and grow. Neutrophils can suppress the anti-tumor immune response by inhibiting the function of other immune cells, such as T cells and natural killer (NK) cells. They can also recruit regulatory T cells and macrophages, contributing to an immunosuppressive environment that allows the tumor to evade immune surveillance.
Cancers Associated with Elevated Neutrophils
Elevated neutrophil counts are frequently observed in various types of cancer, reflecting the complex interplay between the tumor and the immune system. Cancers involving the bone marrow, such as leukemias and myeloproliferative disorders, can directly lead to increased neutrophil production.
Beyond blood cancers, elevated neutrophils can also be associated with solid tumors, including Hodgkin lymphoma and certain lung tumors. While an increased neutrophil count can indicate an inflammatory response induced by a tumor, it is not exclusive to cancer and can vary depending on the specific cancer type and stage.
Prognostic Significance of High Neutrophils in Cancer
Elevated neutrophil counts carry significant prognostic implications for cancer patients. A higher number of circulating neutrophils is often associated with more aggressive disease and a less favorable outlook. This association has been observed in several solid tumors, including melanoma, hepatocellular carcinoma, non-small cell lung carcinoma, and colon cancer.
The neutrophil-to-lymphocyte ratio (NLR), a simple and inexpensive biomarker from routine blood tests, is frequently used as a prognostic factor. A high NLR is correlated with adverse overall survival in many solid tumors, indicating a poorer response to certain treatments and a reduced chance of long-term survival. For example, an elevated NLR has been linked to worse outcomes in patients with metastatic renal cell carcinoma and advanced non-small cell lung cancer. Clinicians consider elevated neutrophil counts as one factor among many when assessing a patient’s prognosis and guiding treatment decisions.