Definition
- White blood cells (leukocytes) are immune system cells that defend the body against infections, foreign antigens, and abnormal cells (including cancer cells).
- Produced in the bone marrow (myeloid and lymphoid lineages).
Major Types of WBCs & Oncology Relevance
| Type | Normal Role | Oncology Relevance |
|---|---|---|
| Neutrophils (50–70%) | First-line defense, phagocytosis of bacteria/fungi | Neutropenia (ANC <500/µL) is a critical complication of chemotherapy → ↑ infection risk. G-CSF (filgrastim, pegfilgrastim) used for prophylaxis/treatment. |
| Lymphocytes (20–40%) | Adaptive immunity (T cells, B cells, NK cells) | Targeted in hematologic malignancies (ALL, CLL, lymphomas). CAR-T, monoclonal antibodies (rituximab, blinatumomab) exploit lymphocyte pathways. |
| Monocytes/Macrophages (2–8%) | Antigen presentation, phagocytosis, cytokine release | Tumor-associated macrophages (TAMs) can promote tumor growth and angiogenesis. |
| Eosinophils (1–4%) | Defense against parasites, allergic responses | May be elevated in some malignancies (Hodgkin lymphoma, T-cell lymphomas). |
| Basophils (<1%) | Release histamine, allergic inflammation | Rarely significant in oncology except in myeloproliferative disorders (e.g., CML). |
WBC Count Reference (Normal Ranges)
- Total WBC: 4,000–10,000/µL
- Absolute Neutrophil Count (ANC): 1,500–8,000/µL
- Mild neutropenia: 1,000–1,500
- Moderate: 500–1,000
- Severe: <500 (high infection risk)
Oncology-Specific Considerations
- Chemotherapy-induced myelosuppression
- Most cytotoxic agents suppress bone marrow → neutropenia, lymphopenia, pancytopenia.
- Leads to febrile neutropenia → requires empiric broad-spectrum antibiotics and sometimes colony-stimulating factors.
- Bone marrow involvement by malignancy
- Leukemias, lymphomas, myeloproliferative neoplasms → abnormal proliferation or suppression of normal WBCs.
- Immunotherapy effects
- Checkpoint inhibitors (e.g., anti–PD-1, CTLA-4) activate lymphocytes but can cause immune-related adverse events.
- CAR-T therapy causes cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity (ICANS).
- Supportive care in oncology
- Growth factors: G-CSF (filgrastim, pegfilgrastim) prevent/treat neutropenia.
- Infection prophylaxis: Antibiotics, antifungals, antivirals in prolonged neutropenia.
- Monitoring: CBC with differential to track marrow suppression and recovery.
Key Clinical Pearl for Oncology Pharmacists
- The absolute neutrophil count (ANC) is the most important WBC parameter in oncology.
- Most oncology treatment decisions (dose reductions, G-CSF use, prophylaxis) are guided by ANC, duration of neutropenia, and presence of fever.