B-cell acute lymphoblastic leukemia (B-cell ALL) is a cancer of the blood and bone marrow, marked by uncontrolled growth of immature B-lymphoblasts. These abnormal cells accumulate in the bone marrow, interfering with healthy blood cell production and spreading throughout the body. The disease progresses rapidly, often over days or weeks, hence “acute.”
B-cell ALL is the most common subtype of acute lymphoblastic leukemia, accounting for about 85% of all ALL cases. It is particularly prevalent in children under six, but also affects adults, representing about 75% of adult ALL cases.
Symptoms and Risk Factors
Symptoms
Symptoms of B-cell ALL arise from the bone marrow’s inability to produce healthy blood cells, including:
Persistent fatigue, paleness, or shortness of breath (anemia from low red blood cells).
Frequent fevers and recurrent infections (shortage of normal white blood cells, especially neutrophils).
Easy bruising or unexplained bleeding (low platelet count, impacting blood clotting).
Pain in bones or joints (overcrowding of bone marrow with leukemic cells).
Swollen lymph nodes, enlarged liver, or enlarged spleen (abnormal B-cell accumulation).
Risk Factors
Several factors increase B-cell ALL likelihood, though they don’t guarantee onset. Age plays a role, peaking in early childhood (two to five years) and again after 50. Inherited genetic conditions like Down syndrome, Li-Fraumeni syndrome, or Klinefelter syndrome, link to higher risk.
Previous cancer treatment, especially chemotherapy or radiation, is another risk factor. While the exact cause is often unknown, environmental exposures like significant radiation are considered. Evidence for other factors like electromagnetic fields remains unclear.
The Diagnostic Process
Initial Assessment
Diagnosis of B-cell ALL begins with a physical exam and medical history review for common symptoms. Doctors look for pale skin, bruising, enlarged lymph nodes, liver, or spleen. These observations guide further investigation.
Blood Tests
Blood tests, especially a complete blood count (CBC), are primary diagnostic tools. A CBC measures red blood cells, white blood cells, and platelets, often revealing abnormal counts. This may include high immature white blood cells (lymphoblasts), low red blood cells (anemia), and low platelets.
Bone Marrow Aspiration and Biopsy
The definitive test for B-cell ALL is a bone marrow aspiration and biopsy. A small sample of liquid bone marrow and bone is collected, usually from the hip. Samples are examined under a microscope to identify lymphoblasts; ALL is diagnosed if blast cells exceed 20% of bone marrow cells.
Specialized Laboratory Tests
Specialized laboratory tests characterize leukemia cells from bone marrow samples. Flow cytometry identifies the specific leukemia type by detecting cell surface markers, confirming B-lymphoblasts. Cytogenetic and molecular tests look for chromosomal changes or genetic mutations, such as the Philadelphia chromosome (translocation between chromosomes 9 and 22), found in about 25% of adults and 3% of children. These genetic findings are important for determining the B-cell ALL subtype, guiding treatment, and informing prognosis.
Treatment Approaches
Treatment for B-cell ALL is divided into distinct phases to achieve and maintain remission.
Induction Therapy
This initial intensive phase rapidly eliminates leukemia cells from blood and bone marrow to achieve remission. Lasting 4-6 weeks, it aims to restore normal blood cell production and reduce bone marrow blast cells to less than 5% (complete remission).
Consolidation Therapy
Following induction, this phase targets remaining leukemia cells to prevent relapse. It often involves different or higher doses of chemotherapy drugs and usually lasts several months, further reducing disease burden.
Maintenance Therapy
The final, longer, less intensive phase prevents leukemia recurrence. Lasting two to three years, it typically involves oral chemotherapy, sometimes with periodic intravenous treatments. This prolonged therapy helps eliminate microscopic residual disease that could lead to relapse.
Chemotherapy
This primary treatment uses drugs to kill rapidly dividing cells, including cancer cells. It is administered in various combinations and dosages across all treatment phases.
Targeted Therapy
Used for specific cases, especially those with genetic markers like the Philadelphia chromosome. Drugs like tyrosine kinase inhibitors (TKIs) such as imatinib or dasatinib block pathways promoting cancer cell growth.
Immunotherapy
This modern approach harnesses the immune system to fight cancer. Chimeric antigen receptor (CAR) T-cell therapy, for example, modifies a patient’s T-cells to recognize and attack leukemia cells. These modified T-cells are infused back, offering a highly specific attack, often for relapsed or resistant disease.
Stem Cell Transplant
Also known as a bone marrow transplant, this intensive option is typically reserved for high-risk B-cell ALL or relapse. It involves high-dose chemotherapy or radiation to destroy diseased bone marrow, followed by infusion of healthy donor stem cells. These new stem cells engraft and produce healthy blood cells, replacing the cancerous marrow.
Prognosis and Remission
Understanding Remission
Remission in B-cell ALL means no detectable leukemia cells in bone marrow or blood, with normal blood counts returned. Achieving remission is the initial treatment goal, indicating a positive response. However, remission does not necessarily mean a cure, as microscopic leukemia cells can still exist.
Survival Rates
The prognosis for B-cell ALL varies significantly between children and adults. Children generally have a more favorable outlook, with five-year survival rates exceeding 90%. For adults over 20, the five-year survival rate is considerably lower, around 40%. This difference is due to variations in disease biology and adult treatment response.
Factors Influencing Prognosis
Several factors influence prognosis. Age at diagnosis is significant; very young children (infants) and older adults typically have a less favorable outlook. Initial white blood cell count can also impact outcomes, with very high counts often linked to higher risk. Specific genetic abnormalities, like the Philadelphia chromosome, also affect prognosis, often requiring targeted therapies.
Relapse and Follow-up
Despite achieving remission, relapse is always possible, where leukemia cells return. Relapse can occur months or years after initial treatment, necessitating further therapy. Follow-up care is a long-term process, involving regular monitoring for disease recurrence. This surveillance helps detect any return early, allowing prompt intervention.