Leukemias, Lymphomas & Myeloproliferative Disorders

Blood cancers begin in the bone marrow or lymphoid tissue. Leukemias are white-blood-cell cancers that flood blood and marrow with immature blasts; lymphomas are lymphocyte cancers forming solid tumors in lymph nodes; myeloproliferative disorders overproduce mature blood cells. Together they are the most common childhood cancers and a major adult group.

This matters because their symptoms — unexplained fever, bleeding, fatigue, swollen nodes — must be recognized early, and because treatment is a success story: childhood acute lymphoblastic leukemia is cured in over 85 percent of cases, and chronic myeloid leukemia is controlled for decades with one daily pill (imatinib).

Key Concepts

• Acute vs chronic leukemia: acute (ALL, AML) — aggressive, ≥20 percent marrow blasts, onset over weeks; chronic (CLL, CML) — mature-looking cells, course over years. ALL peaks at ages 2–5; CLL affects older adults.
• Philadelphia chromosome: t(9;22) creating the BCR-ABL fusion gene in nearly all CML — a constantly active kinase blocked by imatinib, the first targeted cancer drug.
• Hodgkin vs non-Hodgkin lymphoma: Hodgkin contains Reed–Sternberg cells ("owl-eye" nuclei) and spreads node-to-node; non-Hodgkin lymphomas (diffuse large B-cell, follicular, Burkitt) spread less predictably. Both present with painless node enlargement.
• Myeloproliferative neoplasms: polycythemia vera (too many red cells; JAK2 mutation in ~95 percent), essential thrombocythemia (too many platelets), primary myelofibrosis (marrow replaced by scar).
• B symptoms: fever, drenching night sweats, and >10 percent weight loss in 6 months — worsen staging and prognosis.
• Tumor lysis syndrome: massive chemotherapy cell kill releases potassium, phosphate and uric acid, risking kidney failure and arrhythmia — prevented with hydration and allopurinol.

How It Works

1. Mutation: a stem cell acquires growth-control mutations (BCR-ABL, JAK2).
2. Clonal expansion: in acute leukemia, blasts crowd out normal marrow — red cells and platelets fall (anemia, bleeding) while useless blasts flood the blood.
3. Spread: leukemic cells circulate everywhere; lymphoma travels through lymphatics to nodes, spleen and liver. CNS sanctuary sites need preventive intrathecal chemotherapy in ALL.
4. Diagnosis: blood smear, marrow blast percentage, flow cytometry markers, and cytogenetics (Philadelphia chromosome).
5. Treatment: induction, consolidation and maintenance chemotherapy; targeted drugs (imatinib, rituximab); stem-cell transplant for high-risk or relapsed disease.

Worked Example

A marrow report counts 500 nucleated cells with 150 blasts. Step 1: blast percentage — 150 ÷ 500 = 30 percent. Step 2: the acute-leukemia cutoff is ≥20 percent blasts; 30 percent exceeds it. Step 3: flow cytometry shows myeloid markers (CD13, CD33) — diagnosis: acute myeloid leukemia (AML). Step 4: start induction chemotherapy with tumor lysis precautions (IV fluids, allopurinol).

Common Misconceptions

• "Leukemia and lymphoma are the same." Leukemia is a marrow/blood disease with circulating blasts; lymphoma is a solid nodal tumor. Different presentation, staging and treatment.
• "High white cells always mean leukemia." Infections cause reactive leukocytosis with mature neutrophils; leukemia shows blasts. The smear makes the diagnosis.
• "CML needs a transplant to survive." Imatinib turned CML into a manageable chronic disease; transplant is reserved for resistant cases.

Real-World Applications

• Pediatric oncology: risk-stratified ALL protocols cure most children; minimal residual disease testing guides intensity.
• Targeted therapy: imatinib and rituximab are the models for all modern precision cancer drugs.
• Diagnostics: flow cytometry and FISH for the Philadelphia chromosome turn a smear finding into a molecular diagnosis within days.
• Supportive care: tumor lysis protocols and infection prophylaxis during neutropenia keep chemotherapy survivable.

Leukemias flood blood and marrow with blasts, lymphomas grow as nodal tumors, and myeloproliferative disorders overproduce mature cells — each defined by its cell of origin, driver mutation and blast percentage. Find the clone, name the mutation, count the blasts.