Definition, Diagnostic Criteria & Classification

Question	Answer
1. Define Acute Lymphoblastic Leukemia (ALL) and its diagnostic threshold on bone marrow examination.	Acute Lymphoblastic Leukemia is a malignant clonal neoplasm of lymphoid progenitor cells (lymphoblasts) committed to B- or T-cell lineage, characterized by uncontrolled proliferation in the bone marrow cavity and suppression of normal hematopoiesis. - Diagnostic Threshold: Demonstration of $\ge 20\%$ lymphoblasts (WHO classification) or historically $\ge 25\%$ (FAB classification) of all nucleated cells on bone marrow aspiration or trephine biopsy.
2. Detail the NCI (National Cancer Institute) Risk Stratification for pediatric B-ALL.	Stratified at initial diagnosis based on two clinical variables: 1) Standard Risk (SR): Age $1.00\text{ to } 9.99\text{ years}$ AND initial Total Leukocyte Count (TLC) $<50,000/\mu\text{L}$. 2) High Risk (HR): Age $\ge 10.0\text{ years}$ OR initial TLC $\ge 50,000/\mu\text{L}$. - Note: Infants ($<1\text{ year}$) represent a distinct very high-risk category, predominantly driven by $KMT2A$ (MLL) rearrangements.
3. What are the immunophenotypic markers defining B-ALL vs T-ALL on flow cytometry?	- B-Cell ALL (Pre-B ALL / Common ALL, ~85% of cases): Expresses B-lineage markers: CD19, CD10 (CALLA), CD22, CD20, and intracellular cytoplasmic CD79a (cCD79a) and cCD22. - T-Cell ALL (~15% of cases): Expresses T-lineage markers: CD3 (cytoplasmic and surface CD3 is lineage-definitive), CD7, CD5, CD2, CD4, CD8, and lacks surface immunoglobulins. - Lineage-negative markers: CD34 (stem cell) and TdT (Terminal deoxynucleotidyl transferase) are positive in immature lymphoblasts of both lineages.
4. What are the favorable and unfavorable cytogenetic abnormalities in pediatric B-ALL?	- Favorable Cytogenetics: 1) Hyperdiploidy ($>50$ chromosomes or DNA index $>1.16$): Highly sensitive to methotrexate; excellent event-free survival ($>90\%$). 2) $t(12;21)(p13;q22)$ encoding $ETV6\text{-}RUNX1$ (TEL-AML1): Present in $25\%$ of pediatric ALL; confers superior cure rates ($>90\%$). - Unfavorable / High-Risk Cytogenetics: 1) $t(9;22)(q34;q11.2)$ encoding $BCR\text{-}ABL1$ (Philadelphia chromosome): Requires upfront Tyrosine Kinase Inhibitor (Imatinib / Dasatinib). 2) $KMT2A$ ($11q23$ / MLL) Gene Rearrangements ($t(4;11)$): Common in infants; confers poor response and early relapse. 3) Hypodiploidy ($<44$ chromosomes): Very poor prognosis. 4) $t(1;19)(q23;p13.3)$ encoding $TCF3\text{-}PBX1$ (E2A-PBX1): Requires intensified therapy.
5. VIVA TRAP: A general practitioner starts oral Dexamethasone for suspected JIA in a child with prolonged fever and limp. Why is this a catastrophic clinical error?	Lysis of Leukemic Blasts & Obscuration of Diagnosis: Corticosteroids are acutely cytotoxic to lymphoblasts. Administering even a single dose of steroids causes rapid, massive apoptosis of circulating and marrow blasts within 24 to 48 hours. This induces unclassifiable marrow aplasia or 'normalization' of counts, masking the underlying leukemia, delaying life-saving chemotherapy, rendering subsequent flow cytometry and cytogenetics completely uninterpretable, and predisposing the child to unrecognized acute Tumor Lysis Syndrome at home!

Pathophysiology & Complications

Question	Answer
6. Detail the Cairo-Bishop Diagnostic Criteria for Tumor Lysis Syndrome (TLS).	Stratified into Laboratory TLS (LTLS) and Clinical TLS (CTLS): - Laboratory TLS: Defined by $\ge 2$ of the following metabolic derangements occurring simultaneously within 3 days before or 7 days after starting chemotherapy: 1) Hyperuricemia: Serum Uric Acid $\ge 8.0\text{ mg/dL}$ (or $25\%$ increase from baseline). 2) Hyperkalemia: Serum Potassium $\ge 6.0\text{ mEq/L}$ (or $25\%$ increase). 3) Hyperphosphatemia: Serum Phosphorus $\ge 6.5\text{ mg/dL}$ in children (or $25\%$ increase). 4) Hypocalcemia: Corrected Serum Calcium $\le 7.0\text{ mg/dL}$ (or $25\%$ decrease). - Clinical TLS: Presence of Laboratory TLS PLUS at least one of the following clinical complications: - Cardiac Arrhythmia or sudden death. - Acute Kidney Injury (Creatinine $\ge 1.5\times$ upper limit of normal for age). - Seizures or altered neuromuscular irritability (tetany).
7. What are the extramedullary sanctuaries of ALL, and why do they require special therapy?	The two classical sanctuaries are the Central Nervous System (CNS) and the Testes: - Mechanism: The Blood-Brain Barrier (BBB) and the Blood-Testis Barrier possess tight endothelial junctions and P-glycoprotein efflux pumps that block the penetration of standard systemic hydrophilic chemotherapy (Vincristine, Anthracyclines). - Leukemic blasts sequestered in these sites survive systemic induction, leading to isolated CNS or testicular relapse. - Management: Mandates proactive prophylactic therapy: Scheduled Triple Intrathecal Chemotherapy (Methotrexate + Cytarabine + Hydrocortisone) for the CNS, and high-dose systemic Methotrexate with prolonged maintenance.
8. VIVA TRAP: A 5-year-old child with newly diagnosed B-ALL has an initial TLC of 180,000/uL. What is the immediate life-threatening danger, and how is it managed?	Hyperleukocytosis & Leukostasis Syndrome: A WBC $>100,000/\mu\text{L}$ markedly increases whole blood viscosity. Circulating lymphoblasts are rigid and form intravascular aggregates, plugging microvessels in the lungs (pulmonary leukostasis $\to$ hypoxemic respiratory failure) and brain (cerebral leukostasis $\to$ intracranial hemorrhage, stroke). Emergency Management Rules: 1) Strict Rule: DO NOT transfuse packed red blood cells! Raising hematocrit rapidly increases whole blood viscosity precipitously, triggering fatal stroke! Keep $\text{Hb} < 8-9\text{ g/dL}$ until WBC drops. 2) Vigorous hyperhydration ($3000\text{ mL/m}^2/\text{day}$) with rasburicase. 3) Emergency Leukapheresis or rapid cytoreductive steroid prophase.

Guidelines & Management Protocols (ICMR / BFM Protocols)

Question	Answer
9. Detail the multi-phase chemotherapy structure for pediatric ALL.	Modern therapy spans 2 to 2.5 years through five distinct phases: 1) Induction Phase (4–5 weeks): Goal is complete morphological remission ($M1$ marrow, blasts $<5\%$). 3-drug induction (Prednisolone, Vincristine, L-Asparaginase) for Standard Risk; 4-drug induction (+ Daunorubicin) for High Risk. 2) Consolidation / Early Intensification (4–8 weeks): High-Dose Methotrexate ($2-5\text{ g/m}^2$) with Leucovorin rescue, 6-Mercaptopurine, and intrathecal therapy. 3) Interim Maintenance: Lower-intensity chemotherapy allowing marrow recovery. 4) Re-Induction / Delayed Intensification: Repeats induction-like blocks to eradicate resistant clones. 5) Maintenance Phase: Daily oral 6-MP ($50\text{ mg/m}^2$) + Weekly oral Methotrexate ($20\text{ mg/m}^2$) for 2 years in females and 2.5 years in males.
10. Define Minimal Residual Disease (MRD) and its prognostic impact.	- Definition: Detection of submicroscopic leukemic blast persistence below the morphological limit of detection ($<5\%$) using multiparametric 8-color flow cytometry or immunoglobulin/T-cell receptor gene rearrangements by real-time PCR or NGS. - Threshold: Assessed at Day 33 (End of Induction). - MRD-Negative ($<0.01\%$ or $<10^{-4}$): Correlates with superior 5-year event-free survival ($>90\%$). - MRD-Positive ($\ge 0.01\%$): Powerful adverse predictor of relapse; requires treatment intensification with High-Risk blocks, Blinatumomab (BiTE), or Allogeneic HSCT.
11. Outline the "Golden Hour" protocol for Febrile Neutropenia in a child on chemotherapy.	- Criteria: Temperature $\ge 38.3^\circ\text{C}$ (or $\ge 38.0^\circ\text{C}$ sustained $>1\text{ hour}$) with $\text{ANC} < 500/\mu\text{L}$. - The 60-Minute Rule: Empirical IV broad-spectrum antipseudomonal monotherapy must be infused within 60 minutes of presentation! - First-Line Drug: IV Piperacillin-Tazobactam ($300\text{ mg/kg/day}$ divided q6h) or Cefepime ($150\text{ mg/kg/day}$ divided q8h). - When to add Vancomycin: Only if hemodynamic shock, central line tunnel infection, severe mucositis, or MRSA colonization is present. - Persistent Fever at 96 Hours: Perform HRCT chest, serum galactomannan, and add IV Liposomal Amphotericin B ($3-5\text{ mg/kg/day}$).

VIVA TRAPs & Counter-Questions

Question

Answer

12. VIVA TRAP: What is the mechanism of action, unique toxicities, and monitoring for L-Asparaginase?

- Mechanism: Leukemic lymphoblasts lack the enzyme asparagine synthetase and depend entirely on circulating extracellular L-asparagine. L-Asparaginase hydrolyzes asparagine into aspartic acid and ammonia, starving lymphoblasts of an essential amino acid and inducing apoptosis.
- Unique Toxicities:
1) Acute Pancreatitis: Monitor serum amylase and lipase; permanent discontinuation if hemorrhagic pancreatitis occurs.
2) Thrombosis & Hemorrhage: Depletes hepatic synthesis of both procoagulant and anticoagulant proteins (Antithrombin III, Fibrinogen); monitor fibrinogen and D-dimer.
3) Hypersensitivity / Anaphylaxis: Neutralizing anti-asparaginase antibodies (silent inactivation); switch to Erwinia asparaginase.

13. Counter-Question Chain: "How do you differentiate leukemic bone pain from Juvenile Idiopathic Arthritis (JIA) at the bedside?"

1) Pain Timing & Severity: Leukemic pain is severe, deep, nocturnal, wakes the child from sleep, and concentrates in the metaphyses/shins; JIA pain is morning stiffness with gel phenomenon.
2) Fever: ALL fever is irregular or high septic; sJIA fever is classically quotidian with rapid return to normal/subnormal baseline.
3) Joint Examination: ALL causes exquisite bone tenderness upon gentle pressure over non-joint areas (e.g., lower sternum, anterior tibia); JIA causes true synovial effusion with joint line tenderness.
4) Complete Blood Count: ALL shows cytopenias (anemia, thrombocytopenia, neutropenia); sJIA shows reactive thrombocytosis ($>600,000/\mu\text{L}$) and neutrophilic leukocytosis!