USMLE Step 1 & 2 Leukemia and Lymphoma

Last updated: May 2, 2026

Leukemia and Lymphoma questions are one of the highest-leverage areas to study for the USMLE Step 1 & 2. This guide breaks down the rule, the elements you need to recognize, the named traps that catch most students, and a memory aid that scales to test day. Read it once, then practice the same sub-topic adaptively in the app.

The rule

Leukemias are bone marrow malignancies of hematopoietic precursors that spill into blood; lymphomas are solid tumors of lymphoid tissue (nodes, spleen, extranodal sites). For both, your first triage is age and cell line: ALL in kids, AML in older adults, CLL in adults over 60, CML in middle age with massive splenomegaly, Hodgkin in bimodal age peaks with Reed-Sternberg cells, non-Hodgkin grouped by aggressive (DLBCL, Burkitt) vs indolent (follicular). Once you place the patient in the right box, the buzzword (Auer rods, smudge cells, starry sky, Philadelphia chromosome, EBV, t(14;18)) confirms the answer.

Elements breakdown

Acute Lymphoblastic Leukemia (ALL)

Malignant proliferation of immature lymphoid blasts, predominantly B-cell.

  • Peak age 2-5 years
  • Bone pain, fever, pancytopenia
  • TdT positive blasts
  • CD10, CD19, CD20 (B-ALL)
  • t(12;21) good prognosis in kids
  • Down syndrome association

Common examples:

  • Child with limp and bruising
  • Mediastinal mass in T-ALL adolescent

Acute Myeloid Leukemia (AML)

Proliferation of immature myeloid blasts (>20% in marrow).

  • Median age ~65
  • Auer rods (especially APL)
  • Myeloperoxidase positive
  • t(15;17) = APL, treat with ATRA
  • DIC at presentation in APL
  • Prior chemo or MDS history

Chronic Lymphocytic Leukemia (CLL)

Clonal expansion of mature but functionally incompetent B cells.

  • Age >60, often asymptomatic
  • Lymphocytosis on routine CBC
  • Smudge cells on smear
  • CD5, CD19, CD20, CD23 positive
  • Warm autoimmune hemolytic anemia
  • Richter transformation to DLBCL

Chronic Myeloid Leukemia (CML)

Myeloproliferative neoplasm driven by BCR-ABL fusion.

  • Age 45-65
  • Massive splenomegaly
  • Leukocytosis with left shift
  • Low leukocyte alkaline phosphatase
  • Philadelphia chromosome t(9;22)
  • Imatinib first-line therapy

Hodgkin Lymphoma

Lymphoma defined by Reed-Sternberg cells in a reactive cellular background.

  • Bimodal: 20s and >55
  • Painless cervical lymphadenopathy
  • B symptoms (fever, night sweats, weight loss)
  • Contiguous nodal spread
  • CD15, CD30 positive RS cells
  • Nodular sclerosing most common

Diffuse Large B-Cell Lymphoma (DLBCL)

Most common aggressive non-Hodgkin lymphoma in adults.

  • Rapidly enlarging nodal or extranodal mass
  • Median age ~64
  • CD20 positive
  • Aggressive but curable with R-CHOP
  • Can arise from CLL (Richter)

Follicular Lymphoma

Indolent B-cell lymphoma of germinal-center origin.

  • Painless waxing-waning lymphadenopathy
  • t(14;18) BCL2 overexpression
  • CD10, CD20 positive
  • Adults, median age ~60
  • Can transform to DLBCL

Burkitt Lymphoma

Highly aggressive B-cell lymphoma with MYC translocation.

  • Endemic: jaw mass, EBV-associated, African child
  • Sporadic: abdominal mass, ileocecal
  • Starry sky on histology
  • t(8;14) c-MYC
  • Tumor lysis syndrome risk
  • Ki-67 nearly 100%

Multiple Myeloma (boundary case)

Plasma cell malignancy producing monoclonal immunoglobulin.

  • CRAB: hyperCalcemia, Renal failure, Anemia, Bone lesions
  • Punched-out lytic skull lesions
  • M-spike on SPEP
  • Rouleaux on smear
  • Bence-Jones proteinuria

Common patterns and traps

The Age-First Triage

USMLE leukemia/lymphoma vignettes lead with demographics for a reason. Pediatric pancytopenia with bone pain almost always points to ALL; an incidental lymphocytosis in an asymptomatic 70-year-old points to CLL; a middle-aged adult with night sweats and a palpable spleen crossing the umbilicus points to CML. Reading the age line first prevents you from getting trapped by a single overlapping finding.

The vignette opens with 'A 4-year-old boy' or 'A 68-year-old woman with no symptoms,' and the right answer is the leukemia subtype that matches that age peak even before you confirm the cell-line markers.

The Buzzword-to-Translocation Map

Every classic leukemia/lymphoma has a translocation or marker that, when present, is essentially diagnostic on Step exams: t(9;22) BCR-ABL = CML, t(15;17) PML-RARA = APL, t(8;14) c-MYC = Burkitt, t(14;18) BCL2 = follicular, t(11;14) cyclin D1 = mantle cell. The trap is when the question gives you the translocation and asks for the drug or mechanism rather than the diagnosis.

The stem ends '...karyotype shows t(15;17). Which of the following is the most appropriate initial therapy?' and the right answer is all-trans retinoic acid (ATRA), not standard induction chemo.

The DIC-in-APL Misdirection

Acute promyelocytic leukemia (AML M3) frequently presents with disseminated intravascular coagulation because the abnormal promyelocyte granules release procoagulant material. Candidates fixate on the bleeding/clotting picture, work it up as a primary hematologic emergency, and miss that the underlying problem is leukemia requiring urgent ATRA. The smear showing promyelocytes packed with granules and Auer rods is the giveaway.

A young adult presents with bleeding gums, oozing IV sites, low fibrinogen, prolonged PT/PTT, and elevated D-dimer; the marrow shows hypergranular promyelocytes with Auer rods. The right answer is start ATRA, not just transfuse.

The Indolent-vs-Aggressive Wrong-Answer Pair

Non-Hodgkin lymphoma questions often pair an indolent option (follicular, marginal zone, CLL/SLL) with an aggressive option (DLBCL, Burkitt, mantle cell) as the two best distractors. The clue is tempo: years of waxing-waning adenopathy without symptoms = indolent; weeks of rapidly enlarging mass with B symptoms or LDH sky-high = aggressive. Picking the wrong tempo is how candidates lose this question type.

The vignette describes a 62-year-old with painless cervical nodes that have grown and shrunk over 4 years; choices include both DLBCL and follicular lymphoma. Tempo and t(14;18) point to follicular.

The Smudge-Cell Anchor

Smudge cells on peripheral smear are essentially pathognomonic for CLL on Step exams — they're fragile mature lymphocytes that rupture during slide preparation. If a vignette mentions an elderly patient with lymphocytosis and any mention of smudge cells, the answer is CLL regardless of how the rest of the vignette tries to point you toward CML or a reactive lymphocytosis.

A 72-year-old has WBC 95,000 with 88% lymphocytes and 'numerous smudge cells.' Distractors include CML and viral lymphocytosis; CLL is correct.

How it works

Anchor every vignette on age and cell line first. A 4-year-old with bone pain, pancytopenia, and >20% lymphoblasts on marrow is ALL until proven otherwise; a 68-year-old with incidental lymphocytosis of 80,000 and smudge cells is CLL. When the smear shows blasts with Auer rods in an older adult, you're in AML, and if those blasts are promyelocytes with bleeding from DIC, it's APL with t(15;17), treated with all-trans retinoic acid. Massive splenomegaly with leukocytosis, basophilia, and a low LAP score in a middle-aged patient is CML with Philadelphia chromosome — imatinib targets the BCR-ABL tyrosine kinase. A young adult with painless cervical adenopathy, fevers, night sweats, and Reed-Sternberg cells is Hodgkin lymphoma, while the same painless adenopathy in a 60-year-old that waxes and wanes for years with t(14;18) is follicular lymphoma. The trap is letting one buzzword drag you into the wrong box: tumor lysis can occur in any high-turnover malignancy, but starry sky plus an African child with a jaw mass narrows it to endemic Burkitt.

Worked examples

Worked Example 1

Which of the following is the most likely diagnosis?

  • A Acute myeloid leukemia
  • B B-cell acute lymphoblastic leukemia ✓ Correct
  • C Chronic lymphocytic leukemia
  • D Burkitt lymphoma with leukemic phase

Why B is correct: The combination of a young child (peak age 2-5 years), pancytopenia with bone pain, and a marrow filled with TdT-positive blasts expressing CD10, CD19, and CD20 is the textbook presentation of B-cell ALL. TdT positivity confirms a lymphoid precursor (it is not expressed on mature lymphocytes or myeloid blasts), and the CD10 and CD19 mark the precursor B-cell origin. ALL is the most common pediatric malignancy and the age window plus immunophenotype lock in the diagnosis.

Why each wrong choice fails:

  • A: AML occurs predominantly in older adults (median age ~65) and the blasts would be myeloperoxidase positive with possible Auer rods, not TdT-positive lymphoid markers. The age and immunophenotype both argue strongly against AML. (The Age-First Triage)
  • C: CLL is a disease of adults over 60 with mature CD5/CD19/CD23-positive lymphocytes and smudge cells — not TdT-positive blasts in a 4-year-old with bone pain. CLL almost never occurs in children. (The Age-First Triage)
  • D: Burkitt typically presents as a rapidly enlarging mass (jaw in endemic, abdomen in sporadic) with starry-sky histology and t(8;14) c-MYC; it is mature B-cell and TdT-negative, so the marrow phenotype here doesn't fit. (The Buzzword-to-Translocation Map)
Worked Example 2

Which of the following is the most appropriate initial therapy?

  • A Imatinib
  • B All-trans retinoic acid (ATRA) plus arsenic trioxide ✓ Correct
  • C R-CHOP chemotherapy
  • D Allogeneic stem cell transplant

Why B is correct: This is acute promyelocytic leukemia (APL, AML M3): hypergranular promyelocytes, Auer rods, DIC at presentation, and the diagnostic t(15;17) PML-RARA fusion. ATRA plus arsenic trioxide forces the malignant promyelocytes to differentiate and is the standard initial therapy; it must be started urgently because APL-associated DIC carries high early mortality. APL is the one AML subtype where the targeted differentiation therapy comes before traditional induction chemo.

Why each wrong choice fails:

  • A: Imatinib targets the BCR-ABL tyrosine kinase produced by t(9;22) and is the treatment for CML, not APL. Wrong translocation, wrong disease. (The Buzzword-to-Translocation Map)
  • C: R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, prednisone) is first-line for CD20-positive aggressive B-cell lymphomas like DLBCL, not for any acute leukemia. The marrow finding of promyelocytes excludes lymphoma. (The Indolent-vs-Aggressive Wrong-Answer Pair)
  • D: Allogeneic stem cell transplant is reserved for relapsed/refractory or high-risk leukemias after induction; it is not the initial therapy in newly diagnosed APL, where ATRA-based therapy alone produces very high cure rates. (The DIC-in-APL Misdirection)
Worked Example 3

Which of the following is the most likely diagnosis?

  • A Chronic myeloid leukemia
  • B Mantle cell lymphoma
  • C Chronic lymphocytic leukemia ✓ Correct
  • D Reactive lymphocytosis from viral infection

Why C is correct: An asymptomatic older adult with marked lymphocytosis, smudge cells, and a clonal B-cell population co-expressing CD5, CD19, CD20, and CD23 is the classic immunophenotype of CLL. The CD5/CD23 co-expression in particular separates CLL from mantle cell lymphoma (which is CD5-positive but CD23-negative). Smudge cells are essentially pathognomonic on Step exams — they reflect the fragile mature lymphocytes rupturing during slide prep.

Why each wrong choice fails:

  • A: CML produces a myeloid leukocytosis with a left shift, basophilia, and massive splenomegaly in middle-aged adults, with t(9;22) BCR-ABL and a low leukocyte alkaline phosphatase. The lymphoid phenotype and smudge cells here exclude CML. (The Smudge-Cell Anchor)
  • B: Mantle cell lymphoma is also a CD5-positive B-cell neoplasm, but it is CD23-negative and carries t(11;14) with cyclin D1 overexpression; it usually presents as aggressive lymphadenopathy rather than asymptomatic lymphocytosis with smudge cells. (The Indolent-vs-Aggressive Wrong-Answer Pair)
  • D: Reactive lymphocytosis from a viral process produces polyclonal, atypical lymphocytes (such as Downey cells in EBV mononucleosis), not a monoclonal CD5/CD19/CD23-positive population, and would not persist in an asymptomatic 71-year-old without infectious symptoms. (The Smudge-Cell Anchor)

Memory aid

Age boxes first: ALL=kids, AML=older adults, CML=middle age with big spleen, CLL=elderly with smudge cells. Then buzzwords — Auer rods (AML), smudge cells (CLL), Philadelphia (CML), starry sky (Burkitt), Reed-Sternberg (Hodgkin), t(14;18) (follicular), t(15;17) (APL).

Key distinction

CLL vs CML: both cause leukocytosis in adults, but CLL is mature lymphocytes with smudge cells in someone over 60 (often asymptomatic on routine CBC), while CML is a myeloid left shift with basophilia, massive splenomegaly, low LAP, and the Philadelphia chromosome in middle-aged adults.

Summary

Place the patient in the right age-and-cell-line box, then let the buzzword (Auer rods, smudge cells, Reed-Sternberg, starry sky, Philadelphia chromosome, t(14;18), t(15;17)) lock in the diagnosis.

Practice leukemia and lymphoma adaptively

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Frequently asked questions

What is leukemia and lymphoma on the USMLE Step 1 & 2?

Leukemias are bone marrow malignancies of hematopoietic precursors that spill into blood; lymphomas are solid tumors of lymphoid tissue (nodes, spleen, extranodal sites). For both, your first triage is age and cell line: ALL in kids, AML in older adults, CLL in adults over 60, CML in middle age with massive splenomegaly, Hodgkin in bimodal age peaks with Reed-Sternberg cells, non-Hodgkin grouped by aggressive (DLBCL, Burkitt) vs indolent (follicular). Once you place the patient in the right box, the buzzword (Auer rods, smudge cells, starry sky, Philadelphia chromosome, EBV, t(14;18)) confirms the answer.

How do I practice leukemia and lymphoma questions?

The fastest way to improve on leukemia and lymphoma is targeted, adaptive practice — working questions that focus on your specific weak spots within this sub-topic, getting immediate feedback, and revisiting items you missed on a spaced-repetition schedule. Neureto's adaptive engine does this automatically across the USMLE Step 1 & 2; start a free 7-day trial to see your sub-topic mastery climb in real time.

What's the most important distinction to remember for leukemia and lymphoma?

CLL vs CML: both cause leukocytosis in adults, but CLL is mature lymphocytes with smudge cells in someone over 60 (often asymptomatic on routine CBC), while CML is a myeloid left shift with basophilia, massive splenomegaly, low LAP, and the Philadelphia chromosome in middle-aged adults.

Is there a memory aid for leukemia and lymphoma questions?

Age boxes first: ALL=kids, AML=older adults, CML=middle age with big spleen, CLL=elderly with smudge cells. Then buzzwords — Auer rods (AML), smudge cells (CLL), Philadelphia (CML), starry sky (Burkitt), Reed-Sternberg (Hodgkin), t(14;18) (follicular), t(15;17) (APL).

What's a common trap on leukemia and lymphoma questions?

Confusing CLL with CML based on the word 'leukocytosis' alone

What's a common trap on leukemia and lymphoma questions?

Missing APL when DIC dominates the presentation

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