White blood cells (leukocytes) are a key part of the body’s immune system, defending against infections and diseases. They circulate through the bloodstream and tissues. In cancer patients, their count can vary significantly due to the cancer itself or its treatments. Understanding these changes offers insights into a patient’s health status and treatment response. This article explores how cancer and its therapies impact white blood cell counts.
The Role of White Blood Cells
White blood cells originate in the bone marrow and travel throughout the body to identify and neutralize threats.
There are five main types, each with specialized functions: Neutrophils are the most abundant, primarily targeting bacteria and fungi. Lymphocytes, including T cells and B cells, fight viral infections and produce antibodies.
Monocytes help clean up cellular debris and signal other immune cells. Eosinophils identify and destroy parasites and cancer cells, while basophils are involved in allergic reactions and inflammatory responses.
A normal white blood cell count in healthy adults ranges from 4,000 to 11,000 cells per microliter of blood, though this can vary by age, sex, and laboratory.
How Cancer Directly Impacts WBC Counts
Cancer directly influences white blood cell counts through several mechanisms, independent of treatment. Certain cancers, such as leukemias, originate in the bone marrow, causing uncontrolled proliferation of abnormal white blood cells or their precursors. This leads to high numbers of dysfunctional white blood cells.
Lymphomas, cancers of the lymphatic system, can also affect lymphocyte counts, leading to either an increase or decrease depending on the specific type.
Solid tumors can disrupt white blood cell production if they metastasize to the bone marrow. Cancer cells infiltrating the bone marrow can displace healthy hematopoietic stem cells, decreasing the production of white blood cells.
Cancer can also induce systemic inflammation or increase the risk of infection, both of which can elevate white blood cell counts. The body’s immune response to a tumor or an opportunistic infection can trigger an increase in circulating white blood cells. The specific impact on white blood cell counts, whether an increase or a decrease, depends on the type and stage of the cancer.
How Cancer Treatments Affect WBC Counts
Cancer treatments often cause changes in white blood cell counts. Chemotherapy targets rapidly dividing cells, including cancer cells, but also affects healthy cells in the bone marrow that produce white blood cells. This effect is known as myelosuppression.
Neutropenia, a low count of neutrophils, is a common side effect of chemotherapy. Neutrophils are the first line of defense against bacterial and fungal infections, so their reduction increases a patient’s susceptibility to serious infections. The nadir, or lowest point of the white blood cell count, occurs about 7 to 14 days after a chemotherapy session, making this a high-risk period for infection.
Radiation therapy, when directed at large areas of the body or bones containing active bone marrow, can also cause myelosuppression and lower white blood cell counts. The extent of this effect depends on the radiation dose and the specific area treated.
Targeted therapies, designed to interfere with specific molecules involved in cancer growth, often have fewer systemic side effects than traditional chemotherapy, but some can still impact bone marrow function and decrease white blood cell counts.
Immunotherapies, which harness the body’s own immune system to fight cancer, can also affect white blood cell counts, though often through different mechanisms. Some immunotherapies can cause an initial increase in certain types of white blood cells as the immune system becomes activated, while others can lead to reductions or shifts in white blood cell populations as part of their action or as a side effect. These treatment-induced changes are closely monitored to manage patient health and treatment efficacy.
Understanding What Abnormal Counts Mean
Abnormal white blood cell counts in cancer patients provide clinical information, interpreted within the patient’s overall condition. Leukocytosis, a high white blood cell count, can indicate an infection, a common complication in cancer patients undergoing treatment. It can also signal inflammation or be a direct sign of certain types of leukemia, where the bone marrow overproduces abnormal white blood cells.
Conversely, a low white blood cell count, termed leukopenia, or more specifically neutropenia when neutrophils are low, is a concern. Leukopenia indicates a weakened immune system, leaving the patient more vulnerable to infections. This is relevant for cancer patients whose immune systems may already be compromised by disease or treatment. Severe neutropenia can necessitate delays in cancer treatment or require interventions like growth factor injections to stimulate white blood cell production.
Doctors consider the specific type of cancer, the stage of the disease, the patient’s current symptoms, and the ongoing treatment regimen when interpreting white blood cell counts. While abnormal counts highlight potential problems, a comprehensive medical evaluation is needed to understand their implications and guide management strategies.