3.1 Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common cancer of childhood. Incidence peaks between about 2 and 5 years of age. Most pediatric ALL is B-lymphoblastic leukemia (B-ALL). T-ALL is less common, tends to occur in older children and adolescents, and is classically linked to a mediastinal mass, higher presenting white-cell counts, and bulky nodes.

CPHON items on ALL test whether you can recognize the first presentation, complete the essential workup, distinguish favorable from adverse genetics as examples rather than as an exhaustive catalog, follow the long protocol backbone, and manage the two induction emergencies that kill children early: tumor lysis syndrome (TLS) and infection. Relapse geography—marrow, CNS, and testis—closes the picture.

How children actually present

The history is rarely a parent saying the word leukemia. A preschooler develops an unexplained limp, refuses to walk, or wakes with bone or joint pain. Fever comes and goes. The child looks pale. Parents notice bruises in odd places or pinpoint petechiae on the chest and legs. Lymphadenopathy and hepatosplenomegaly are common on exam. Boys need a testicular examination at diagnosis because the testes are a sanctuary site.

A limp plus cytopenias is leukemia until the marrow says otherwise. Do not let a normal orthopedic radiograph close the workup. Night pain, weight-bearing refusal, and pallor together belong in the emergency department, not a delayed sports-medicine clinic. Families often hear growing pains for weeks before someone orders a complete blood count (CBC).

Blood counts and first labs

The CBC is a screening tool, not a diagnosis. Typical findings are cytopenias—anemia, thrombocytopenia, and neutropenia—with or without circulating blasts. The white-cell count may be low, normal, or very high. A normal WBC does not exclude ALL. Absence of peripheral blasts does not exclude a packed marrow.

Add a chemistry panel with uric acid, potassium, phosphate, calcium, and lactate dehydrogenase (LDH); coagulation studies; blood culture if febrile; and a careful look for bleeding, respiratory distress, and superior vena cava signs. Hyperleukocytosis occurs in ALL, but symptomatic leukostasis is more classic in AML. A very high ALL blast count still drives TLS precautions, hydration, and protocol-based cytoreduction.

Workup that must not be skipped

Diagnosis requires bone marrow morphology, flow-cytometric immunophenotype, and cytogenetics/FISH, often with a molecular panel. CNS status is established by lumbar puncture at diagnosis and reported as CNS-1, CNS-2, or CNS-3 on cooperative-group studies. On contemporary protocols, that diagnostic LP is performed with intrathecal chemotherapy—usually methotrexate, with additional IT agents as the protocol specifies. Do not send a child for a cytology-only LP and then debate later whether CNS prophylaxis has started.

Testicular examination in boys is part of staging, not an afterthought reserved for relapse. Chest imaging is mandatory when T-ALL is possible: an anterior mediastinal mass can collapse the airway or obstruct venous return. Do not sedate that child casually for a diagnostic procedure.

B-ALL versus T-ALL

Lineage is defined by immunophenotype, not by a single physical finding. B-ALL accounts for most pediatric ALL. T-ALL more often presents in older children, with high WBC, adenopathy, and a mediastinal mass. Nursing implications of T-ALL include airway vigilance, higher TLS risk with bulky disease, and protocol-specific CNS and mediastinal management. A teenager with a large anterior mediastinal mass, cough when supine, and a high WBC is a T-lineage emergency until proven otherwise.

Risk features you should be able to teach

Starting risk still uses National Cancer Institute (NCI)/Rome criteria for B-ALL: age 1 to 9.99 years and WBC below 50,000/µL is the usual standard-risk starting point; age 10 years or older or WBC 50,000/µL or higher is high risk. Infants younger than 1 year are treated on infant pathways, not ordinary childhood B-ALL arms. Final risk then adds lineage, CNS and testicular status, early response including measurable residual disease (MRD), and genetics. Teach genetics as examples, not as a scored laundry list:

Ph-like ALL is a concept, not a single FISH probe. Gene-expression or kinase-alteration testing on protocol identifies children who may receive additional targeted therapy and intensive response monitoring. Infant ALL with KMT2A rearrangement is its own high-intensity pathway.

Treatment phases and backbone drugs

Pediatric ALL is treated in named sequential phases over about 2 to 3 years. Total duration is protocol-dependent and often longer in males.

Induction uses a corticosteroid (prednisone or dexamethasone), vincristine, asparaginase, and, for many higher-risk groups, an anthracycline such as daunorubicin. The goal is morphologic remission and a deep MRD response. Consolidation/intensification then attacks residual disease and commonly includes high-dose methotrexate plus continued CNS-directed therapy. Interim maintenance bridges intensive blocks. Delayed intensification is a second intensive course because omitting it historically increased relapse. Maintenance is the longest phase: daily mercaptopurine, weekly methotrexate, periodic vincristine and steroid pulses, and intrathecal therapy per protocol.

CNS prophylaxis is not optional. Intrathecal methotrexate (and other IT agents as specified) plus systemic agents with CNS penetration—high-dose methotrexate and corticosteroids—protect a sanctuary site. Cranial radiation is reserved for selected high-risk CNS disease on modern protocols and is not routine for standard-risk B-ALL.

Induction nursing traps and relapse geography

Induction is the highest-risk window for TLS and infection. Start hydration and uric-acid control (allopurinol or rasburicase per protocol) before or with the first cytoreductive doses whenever possible. Monitor potassium, phosphate, calcium, uric acid, and urine output. Fever during neutropenia is an emergency. Asparaginase adds hypersensitivity, thrombosis, and pancreatitis. Vincristine adds constipation and peripheral neuropathy. Steroids add hyperglycemia, mood change, gastritis, and infection risk. Teach families that counts will fall after therapy starts and that looking better on day 4 does not mean the child is safe at home without precautions. Pneumocystis prophylaxis with trimethoprim-sulfamethoxazole is standard throughout ALL therapy on most protocols.

The three classic relapse sites are bone marrow, CNS, and testis. Isolated CNS or testicular relapse can occur while marrow remains in remission. New limp, headache, morning vomiting, cranial-nerve palsy, or a painless testicular enlargement during or after therapy needs same-day evaluation, not a wait-and-see visit next week.