A complete blood count (CBC) is a common blood test that provides information about the different types of cells in a person’s blood. Among the white blood cells, lymphocytes and neutrophils are two specific types that play distinct roles in the body’s defense system. Variations in their levels, particularly low lymphocytes and high neutrophils, can serve as an indicator of various health conditions, including cancer.
The Role of Lymphocytes and Neutrophils
Lymphocytes are a type of white blood cell central to the adaptive immune system, recognizing and targeting specific threats. There are two main types: T-cells and B-cells. T-cells directly attack infected or cancerous cells and help regulate the immune response, while B-cells produce antibodies that neutralize foreign invaders like bacteria and viruses. Natural killer (NK) cells are part of the innate immune system and can identify and destroy abnormal cells, including tumor cells.
Neutrophils are the most abundant type of white blood cell and are primary responders in the innate immune system. They quickly migrate to sites of infection or inflammation to engulf and destroy pathogens through a process called phagocytosis. Neutrophils also release antimicrobial substances and contribute to the inflammatory response, which helps to recruit other immune cells to the affected area. Their rapid response forms a first line of defense against many infectious agents.
Why Cancer Affects Lymphocyte and Neutrophil Counts
Cancer can significantly alter the balance of lymphocytes and neutrophils. Lymphopenia, or a low lymphocyte count, can occur due to direct effects of the tumor, which may produce factors that destroy lymphocytes or impair their function. Chronic inflammation associated with cancer can also lead to lymphocyte exhaustion or their redistribution away from the bloodstream.
Bone marrow suppression, caused by the cancer itself or its treatments like chemotherapy and radiation therapy, can reduce the production of new lymphocytes. Chemotherapy specifically targets rapidly dividing cells, which includes healthy lymphocytes, leading to a significant drop in their numbers. Nutritional deficiencies can also contribute to lower lymphocyte levels.
Neutrophilia, an elevated neutrophil count, is frequently observed in cancer patients due to tumor-induced inflammation. Tumors can release various signaling molecules, such as granulocyte colony-stimulating factor (G-CSF) and interleukin-6 (IL-6), which directly stimulate the bone marrow to produce and release more neutrophils into circulation. This sustained demand can lead to an increase in immature neutrophils. Certain paraneoplastic syndromes can also contribute to neutrophilia.
Clinical Significance in Cancer
The ratio of neutrophils to lymphocytes, known as the Neutrophil-to-Lymphocyte Ratio (NLR), is a widely used clinical metric that reflects the balance between these two cell types. An elevated NLR is often associated with a poorer prognosis across many cancer types. This includes associations with more aggressive disease progression and reduced effectiveness of certain cancer treatments.
This association stems from an imbalanced immune response where pro-tumor inflammation, often driven by neutrophils, outweighs the anti-tumor immunity that lymphocytes typically provide. Neutrophils, particularly certain subsets, can promote tumor growth, metastasis, and angiogenesis, while suppressing the anti-tumor activity of T-cells through mechanisms like releasing reactive oxygen species and arginase 1. Therefore, a high NLR can serve as an indicator of systemic inflammation and immune dysregulation.
Monitoring and Management of Blood Cell Counts
Routine Complete Blood Counts (CBCs) are regularly performed to monitor lymphocyte and neutrophil levels in cancer patients. This monitoring allows clinicians to track changes in these cell counts, which can provide insights into disease progression or potential complications. For instance, a significantly low lymphocyte count can indicate an increased risk of infection, as these cells fight off pathogens.
This information is considered alongside other diagnostic tools and the overall clinical picture. While blood counts are informative, they are not typically the sole basis for diagnosis or determining prognosis. Monitoring these counts helps healthcare providers anticipate and manage potential side effects of cancer and its treatments, such as increased susceptibility to infections or identifying a persistent inflammatory state.