APL (M3) Emergency
t(15;17) PML-RARA + Auer Rods + DIC → Immediate ATRA (All-Trans Retinoic Acid) + Arsenic Trioxide!
CML vs. Leukemoid Reaction
CML = t(9;22) BCR-ABL1 + LOW LAP Score + Basophilia → Rx: Imatinib / Dasatinib
ALL vs. CLL
ALL: Child, TdT+ / CALLA (CD10)+ + CNS/Testes sanctuary. CLL: Elderly, CD5+ / CD19+ / CD20+ / CD23+ + Smudge Cells
Hodgkin vs. Non-Hodgkin
Hodgkin = CD15+ / CD30+ Reed-Sternberg ('Owl-Eye') Cells + Contiguous spread + Alcohol-induced node pain
High-Yield NHL Translocations
Follicular = t(14;18) BCL2; Mantle Cell = t(11;14) Cyclin D1; Burkitt = t(8;14) c-MYC ('Starry-Sky')
Multiple Myeloma CRAB
HyperCalcemia + Renal Failure (Bence Jones casts) + Anemia (Rouleaux) + Lytic Bone Lesions (≥ 10% plasma cells)
Myeloproliferative Drivers
Polycythemia Vera = JAK2 V617F (>95%, Low EPO, Aquagenic Pruritus, Budd-Chiari); ET & PMF = JAK2 / CALR / MPL
Tumor Lysis Syndrome (TLS)
HIGH Potassium + HIGH Phosphate + HIGH Uric Acid + LOW Calcium → IV Fluids + Rasburicase (Check G6PD!)
The Four Classic Leukemias: High-Yield Board Comparison
Hematologic leukemias are classified by cell lineage (lymphoid vs. myeloid) and maturation kinetics (acute blast arrest with ≥20% bone marrow blasts vs. chronic proliferation of mature-appearing cells) into four canonical board entities: Acute Lymphoblastic Leukemia (ALL), Acute Myeloid Leukemia (AML), Chronic Lymphocytic Leukemia (CLL), and Chronic Myeloid Leukemia (CML). Integrating patient age, peripheral blood smear morphology, immunophenotypic CD markers, and signature cytogenetic translocations establishes the definitive diagnosis and targeted therapy.
| Leukemia | Classic Demographics | Smear & Cytochemistry | Key Genetics & Treatment |
|---|---|---|---|
| AML | Older adults (median 65 yrs) | Myeloblasts > 20%, Auer rods, Myeloperoxidase (MPO) positive | t(15;17) PML-RARA in APL (treat immediately with All-Trans Retinoic Acid / Arsenic Trioxide) |
| ALL | Children (peak 2-5 yrs) | Lymphoblasts > 20%, PAS positive, TdT positive | t(12;21) good prognosis; t(9;22) poor prognosis; mandatory CNS prophylaxis (intrathecal methotrexate) |
| CML | Middle-aged adults (45-65 yrs) | Full spectrum of myeloid precursors (basophils, myelocytes); Low LAP score | t(9;22) Philadelphia chromosome (BCR-ABL1 fusion tyrosine kinase); treat with Imatinib / Dasatinib |
| CLL | Elderly (> 65 yrs) | Mature-appearing small lymphocytes, Smudge cells / basket cells | Co-express CD5 and CD19/CD20; complication: Autoimmune hemolytic anemia (AIHA) or Richter transformation to DLBCL |
Acute Leukemias (ALL vs. AML): TdT+ Lymphoblasts vs. MPO+ Auer Rods & APL t(15;17) ATRA Differentiation
Acute Leukemias present acutely with bone marrow failure—anemia (fatigue/pallor), thrombocytopenia (mucosal bleeding/petechiae), and neutropenia (opportunistic infections)—accompanied by ≥20% blasts on bone marrow biopsy. Acute Lymphoblastic Leukemia (ALL) is the #1 malignancy of childhood (peak age 2–5 years; strongly associated with Down syndrome [Trisomy 21] after age 5); lymphoblasts are positive for nuclear Terminal Deoxynucleotidyl Transferase (TdT+) and CALLA (CD10+), with B-ALL expressing CD19/CD20 (favorable prognosis: t(12;21) TEL-AML1 and hyperdiploidy; poor prognosis: t(9;22) Philadelphia chromosome) and T-ALL presenting in adolescent males as an anterior mediastinal (thymic) mass causing SVC syndrome (expressing CD2–CD8). ALL requires CNS prophylactic intrathecal chemotherapy (methotrexate/cytarabine). Acute Myeloid Leukemia (AML) (median age 65) features myeloblasts positive for Myeloperoxidase (MPO+) containing pathognomonic pink needle-like Auer rods (fused azurophilic granules). Its highest-yield subtype, Acute Promyelocytic Leukemia (APL, M3), is driven by t(15;17) PML-RARA fusion, which blocks promyelocyte differentiation and releases Auer-rod tissue factor, triggering fatal Disseminated Intravascular Coagulation (DIC); treat immediately with All-Trans Retinoic Acid (ATRA, vitamin A derivative) plus Arsenic Trioxide, which degrades PML-RARA and forces promyelocytes to mature into neutrophils (watch for Differentiation Syndrome: fever, pulmonary infiltrates, hypotension—treat with dexamethasone).
Chronic Leukemias: CLL Smudge Cells & Richter Transformation vs. CML t(9;22) BCR-ABL1 vs. Leukemoid Reaction
Chronic Lymphocytic Leukemia (CLL) (identical to Small Lymphocytic Lymphoma [SLL] when nodal) is the most common adult leukemia in Western countries (median age 70), driven by clonal proliferation of naive CD5+ and CD23+ B-lymphocytes (also CD19+/CD20+) that are fragile on peripheral blood smear prep, rupturing into pathognomonic 'Smudge Cells' (parachute cells). Key CLL complications include warm autoimmune hemolytic anemia (IgG), hypogammaglobulinemia (recurrent S. pneumoniae infections), and Richter Transformation—abrupt clinical deterioration with rapidly enlarging lymphadenopathy, drenching night sweats, and LDH surge signaling transformation into aggressive Diffuse Large B-Cell Lymphoma (DLBCL). Symptomatic CLL is treated with BTK inhibitors (ibrutinib, acalabrutinib) or BCL-2 inhibitor (venetoclax). Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm driven by the Philadelphia chromosome t(9;22), creating the constitutively active BCR-ABL1 fusion tyrosine kinase (treated with first-line Imatinib / Dasatinib). CML presents with splenomegaly and extreme leukocytosis showing the full myeloid spectrum (myelocytes, metamyelocytes) plus basophilia. Distinguish CML from a reactive Leukemoid Reaction (severe infection): CML has a LOW Leukocyte Alkaline Phosphatase (LAP) score and basophilia, whereas a Leukemoid Reaction has a HIGH LAP score, toxic granulations, Döhle bodies, and no t(9;22).
Tumor Lysis Syndrome (TLS) Prevention & Management
TLS is an oncologic emergency triggered by massive lysis of malignant cells following chemotherapy initiation (especially Burkitt lymphoma and ALL):
Classic Metabolic Tetrad
- Hyperkalemia: Risk of fatal ventricular arrhythmias
- Hyperphosphatemia: Binds serum calcium
- Hypocalcemia: Tetany, seizures, QT prolongation
- Hyperuricemia: Urate nephropathy & acute renal failure
Prophylaxis Protocol
- IV Hydration: Aggressive pre-chemotherapy saline
- Allopurinol: Xanthine oxidase inhibitor (blocks new uric acid synthesis)
- Rasburicase: Recombinant urate oxidase (breaks uric acid down into soluble allantoin; contraindicated in G6PD)
| Metabolic Abnormality | Intracellular Source & Pathophysiology | Clinical Manifestations | Prophylaxis & Emergency Treatment |
|---|---|---|---|
| Hyperkalemia (Earliest & Most Lethal) | Massive release of intracellular potassium (>140 mEq/L inside blasts) within 6-24 hours of cytotoxic lysis | Peaked T waves, QRS widening, sine-wave ventricular fibrillation / cardiac arrest | IV Calcium Gluconate (cardioprotection) + Regular Insulin with D50W + Sodium Zirconium Cyclosilicate / Hemodialysis |
| Hyperphosphatemia & Secondary Hypocalcemia | Malignant lymphoblasts contain 4x normal intracellular organic/inorganic phosphate; released PO4 binds serum Ca2+ to form calcium-phosphate crystals | Renal tubular nephrocalcinosis, tetany, Chvostek/Trousseau signs, QTc prolongation, seizures | Aggressive IV 0.9% NaCl hydration + oral phosphate binders; do NOT administer IV calcium for asymptomatic hypocalcemia (precipitates metastatic tissue calcification) unless tetany/arrhythmia present |
| Severe Hyperuricemia | Catabolism of released purine nucleic acids (adenine/guanine -> hypoxanthine -> xanthine -> uric acid via xanthine oxidase) | Acute uric acid crystal nephropathy (uric acid precipitates in acidic distal collecting tubules) | Prophylaxis (low/intermediate risk): Allopurinol (inhibits xanthine oxidase, prevents NEW uric acid formation). Active TLS / High risk (uric acid >8 mg/dL, Burkitt/ALL): Rasburicase (recombinant urate oxidase -> converts existing uric acid into soluble allantoin; contraindicated in G6PD deficiency!) |
Interactive 2K Master Atlas Plate
Pathophysiology of the Four Metabolic Derangements & Calcium Phosphate Nephropathy
Tumor Lysis Syndrome (TLS) is an oncologic emergency triggered 12 to 72 hours after initiating cytotoxic chemotherapy, corticosteroids, or rituximab/venetoclax in malignancies with massive proliferative rates or tumor bulk—classically Burkitt Lymphoma, Acute Lymphoblastic Leukemia (ALL), and AML with WBC >100,000/μL. Rapid lysis of millions of malignant cells dumps intracellular ions and nucleic acids into the bloodstream, producing the Cairo-Bishop metabolic tetrad (3 Highs, 1 Low): (1) Severe Hyperkalemia (>6.0 mEq/L)—the earliest and most immediately lethal abnormality (peaked T waves, sine-wave QRS, ventricular fibrillation); (2) Severe Hyperphosphatemia (>4.5 mg/dL) from intracellular phosphate release; (3) Secondary Hypocalcemia (<7.0 mg/dL) because excess serum phosphate chelates free ionized Ca2+ into insoluble calcium phosphate crystals that precipitate in the renal interstitium and tubules, causing tetany, QT prolongation, and seizures; and (4) Severe Hyperuricemia (>8.0 mg/dL) as purine nucleotides (adenine/guanine) are catabolized by xanthine oxidase into poorly soluble uric acid, which precipitates in the acidic distal renal tubules to cause acute obstructive uric acid nephropathy.
Prophylaxis vs. Active TLS Treatment: Allopurinol vs. Rasburicase (and the G6PD Contraindication)
Universal TLS prophylaxis begins 24 to 48 hours prior to chemotherapy with aggressive intravenous isotonic crystalloid hydration (2–3 L/m2/day) to maintain high urine output (>100 mL/hr) without urinary alkalinization (sodium bicarbonate is no longer recommended because alkaline urine accelerates calcium phosphate precipitation!). Pharmacologic urate management depends on risk stratification: for low-to-intermediate risk patients, administer Allopurinol (or Febuxostat), a xanthine oxidase inhibitor that blocks the synthesis of new uric acid from hypoxanthine/xanthine but cannot lower pre-existing serum uric acid levels. For high-risk patients or established TLS (uric acid >8 mg/dL or acute kidney injury), administer Rasburicase, a recombinant urate oxidase enzyme that directly oxidizes existing insoluble uric acid into highly water-soluble allantoin, which is rapidly excreted by the kidneys. CRITICAL BOARD TRAP: Because the enzymatic conversion of uric acid to allantoin by rasburicase generates hydrogen peroxide (H2O2) as a byproduct, Rasburicase is STRICTLY CONTRAINDICATED in patients with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, in whom it precipitates catastrophic oxidative intravascular hemolysis and methemoglobinemia!
Acute & Chronic Leukemias: Molecular Genetics, Flow Cytometry & Targeted Therapy
Leukemias are clonal neoplastic proliferations of hematopoietic stem or progenitor cells originating in the bone marrow and spilling into peripheral blood. They are fundamentally classified along two axes: (1) Cell Maturity (Acute vs. Chronic): Acute Leukemias (≥ 20% bone marrow blasts!) result from a differentiation arrest in immature progenitor blasts (TdT+ in lymphoblasts; MPO+ in myeloblasts), causing rapid bone marrow failure within weeks (anemia → fatigue/pallor; thrombocytopenia → petechiae/mucosal bleeding; neutropenia → opportunistic fever/infection). Conversely, Chronic Leukemias (< 20% blasts) involve proliferation of morphologically mature-appearing but functionally defective leukocytes in older adults, often discovered incidentally or via massive splenomegaly/lymphadenopathy; and (2) Lineage (Lymphoid vs. Myeloid).
| Leukemia Subtype & Peak Age | Immunophenotype & Histochemical Stain | Signature Cytogenetics / Molecular Driver | Pathognomonic Smear & Clinical Clues | First-Line Targeted Therapy |
|---|---|---|---|---|
| Acute Lymphoblastic Leukemia (ALL) Children 2–5 yrs (#1 pediatric cancer!) | TdT+ (terminal deoxynucleotidyl transferase — marker of pre-B & pre-T lymphoblasts!). B-ALL (85%): CD10 (CALLA)+, CD19+, CD20+. T-ALL (15%): CD2–CD8+, CD3+ | t(12;21) ETV6-RUNX1 = GOOD prognosis (children). t(9;22) BCR-ABL1 (Ph+) = POOR prognosis (adults). Strongly associated with Down Syndrome (Trisomy 21 — after age 5) | Bone/joint pain (marrow expansion), hepatosplenomegaly, CNS & Testicular 'sanctuary sites' (require intrathecal methotrexate!). T-ALL presents in adolescent males with an anterior mediastinal (thymic) mass causing SVC syndrome | Multi-agent chemotherapy + Intrathecal Methotrexate; Blinatumomab (CD19/CD3 BiTE) or CAR-T (Tisagenlecleucel) for relapse |
| Acute Myeloid Leukemia (AML) & APL (M3) Older Adults (median ~65 yrs) | Myeloperoxidase (MPO)+, CD13+, CD33+, CD34+ (TdT negative!). Monocytic AML (M4/M5): Non-specific esterase+ | APL (M3): t(15;17) PML-RARA fusion. Core-binding factor AML (good prognosis): t(8;21) or inv(16). Poor prognosis: FLT3-ITD, post-alkylating chemo/radiation, MDS evolution, or Down Syndrome (< 5 yrs: Acute Megakaryoblastic Leukemia M7) | Cytopenias + Auer rods (pink needle-like MPO+ rods). APL (M3) causes fulminant DIC. Acute Monocytic Leukemia (M5) causes gingival hyperplasia (leukemic infiltration of gums!) | APL (M3): ATRA (All-Trans Retinoic Acid) + Arsenic Trioxide. Non-M3 AML: Cytarabine + Idarubicin/Daunorubicin ('7+3') or Venetoclax + Azacitidine |
| Chronic Lymphocytic Leukemia (CLL) / SLL Elderly (> 65 yrs; #1 adult leukemia in West) | Mature-appearing B cells co-expressing CD19+, CD20+, CD23+ AND the aberrant T-cell marker CD5+! | del(13q) (good prognosis); del(17p) / TP53 mutation (very poor prognosis, resistant to chemo) | Often asymptomatic with extreme lymphocytosis, generalized lymphadenopathy, and fragile B cells crushed on slide prep into Smudge Cells (Parachute cells). Complications: Hypogammaglobulinemia (#1 cause of death = infection!), Warm/Cold AIHA, and Richter Transformation to DLBCL | Asymptomatic: Watch and wait. Symptomatic: Ibrutinib / Acalabrutinib (Bruton Tyrosine Kinase [BTK] inhibitors) or Venetoclax (BCL2 inhibitor) |
| Hairy Cell Leukemia Middle-aged Men (~55 yrs) | Mature B-cell neoplasm: CD19+, CD20+, CD11c+, CD25+, CD103+, Annexin A1+; stains positive for TRAP (Tartrate-Resistant Acid Phosphatase) | Activating BRAF V600E point mutation (present in virtually 100% of classic cases!) | Lymphocytes with filamentous hair-like cytoplasmic projections + MASSIVE Splenomegaly + Pancytopenia (especially severe MONOCYTOPENIA) + 'Dry Tap' on bone marrow aspiration (due to marrow reticulin fibrosis) + NO lymphadenopathy! | Cladribine (2-CDA) or Pentostatin (purine nucleoside analogs — achieve > 90% complete remission!) |
| Chronic Myeloid Leukemia (CML) Adults 45–65 yrs | Myeloid proliferation across all maturation stages (myelocytes, metamyelocytes, bands, neutrophils) with LOW Leukocyte Alkaline Phosphatase (LAP) score | Philadelphia Chromosome t(9;22) creating constitutive BCR-ABL1 fusion non-receptor tyrosine kinase | Marked leukocytosis (often > 100,000/μL), absolute BASOPHILIA & eosinophilia, and massive splenomegaly (early satiety/LUQ fullness). Can progress from Chronic Phase → Accelerated Phase → Blast Crisis (≥ 20% myeloid or lymphoid blasts!) | Imatinib, Dasatinib, or Nilotinib (BCR-ABL1 tyrosine kinase inhibitors); Ponatinib for T315I gatekeeper mutation |
BCR-ABL1 Non-Polycythemia Myeloproliferative Neoplasms: PV vs. ET vs. Primary Myelofibrosis
The three classic Philadelphia-chromosome-NEGATIVE (BCR-ABL1 negative) Myeloproliferative Neoplasms (MPNs) are driven by constitutive activation of the JAK2–STAT signaling pathway (downstream of EPO and TPO receptors): (1) Polycythemia Vera (PV): > 95% harbor the JAK2 V617F mutation, causing autonomous proliferation of RBCs (Hgb > 16.5 g/dL in men, > 16.0 g/dL in women), granulocytes, and platelets with SUPPRESSED serum EPO. Classic clinical clues: aquagenic pruritus (intense itching after a warm shower due to mast cell/basophil histamine release), erythromelalgia (burning, fiery-red painful hands/feet from microvascular platelet sludging—relieved dramatically by aspirin), facial plethora, and hepatic vein thrombosis (Budd-Chiari syndrome). Treat with serial therapeutic phlebotomy (target Hct < 45%) + low-dose Aspirin (± Hydroxyurea or Ruxolitinib); (2) Essential Thrombocythemia (ET): JAK2 V617F (50%) or CALR / MPL mutation causing isolated massive megakaryocyte/platelet proliferation (platelets > 450,000–1,000,000/μL) with thrombosis, erythromelalgia, and paradoxical bleeding (acquired von Willebrand syndrome); and (3) Primary Myelofibrosis (PMF): neoplastic megakaryocytes secrete PDGF and TGF-β, stimulating bone marrow fibroblasts to deposit dense collagen/reticulin fibrosis → 'Dry tap' bone marrow aspiration, massive splenomegaly (extramedullary hematopoiesis), and Leukoerythroblastic blood smear showing Dacrocytes (Teardrop RBCs) + nucleated RBCs.
Adult T-Cell Leukemia/Lymphoma (HTLV-1) vs. Mycosis Fungoides / Sezary Syndrome
Two mature CD4+ T-cell malignancies have unmistakable board presentations: (1) Adult T-Cell Leukemia/Lymphoma (ATLL): caused by Human T-Lymphotropic Virus-1 (HTLV-1), endemic to Japan, the Caribbean, and West Africa. It presents with ulcerating skin lesions, lytic bone lesions, severe HYPERCALCEMIA, lymphadenopathy, and peripheral blood smear showing malignant CD4+ T cells with hyperlobulated 'Cloverleaf' or 'Flower-like' nuclei (do NOT confuse with Multiple Myeloma, which also has lytic bone lesions and hypercalcemia, but has Rouleaux, renal failure, M-spike, and plasma cells!); and (2) Mycosis Fungoides & Sézary Syndrome: cutaneous CD4+ T-cell lymphoma presenting initially with chronic pruritic erythematous skin patches/plaques and Pautrier microabscesses (intraepidermal aggregates of malignant T cells on skin biopsy). When the malignant CD4+ T cells disseminate into the peripheral blood with generalized exfoliative erythroderma ('Red Man Syndrome'), it is called Sézary Syndrome, characterized on blood smear by CD4+ T cells with folded, grooved 'Cerebriform' (brain-like) nuclei.
Hematopoietic Stem Cell Transplantation: Acute vs. Chronic Graft-Versus-Host Disease (GVHD)
Following allogeneic hematopoietic stem cell transplantation (HSCT) for AML, ALL, or MDS, immunocompetent donor T lymphocytes recognize recipient MHC/minor histocompatibility antigens as foreign, triggering Graft-Versus-Host Disease (GVHD) (a Type IV cell-mediated hypersensitivity reaction that also provides a beneficial Graft-Versus-Leukemia [GVL] effect!). Acute GVHD (< 100 days post-transplant) targets three classic organs: (1) Skin: painful maculopapular rash starting on the palms, soles, and ears that can progress to toxic epidermal necrolysis-like desquamation; (2) Liver: cholestatic jaundice with elevated direct bilirubin and alkaline phosphatase; and (3) GI Tract: profuse watery/bloody secretory diarrhea and abdominal cramping.
Hodgkin vs. Non-Hodgkin Lymphomas: Reed-Sternberg Pathology & Translocation Atlas
Lymphomas are solid neoplasms of lymphoid tissue (lymph nodes, spleen, MALT) divided into Hodgkin Lymphoma (HL) and Non-Hodgkin Lymphoma (NHL). Hodgkin Lymphoma (~10–15% of lymphomas) exhibits a bimodal age distribution (peaks at ~20–30 years and > 60 years), spreads in a predictable contiguous fashion from one lymph node group to the next, rarely involves extranodal sites or the leukemic bloodstream, and is defined histologically by the presence of Reed-Sternberg (RS) cells—giant binucleate or bilobed B-origin tumor cells with prominent eosinophilic inclusion-like nucleoli ('Owl-Eye' nuclei) that are CD15+ and CD30+ (and CD20 negative / CD45 negative), surrounded by a dense reactive background of non-neoplastic lymphocytes, eosinophils, macrophages, and fibroblasts.
| Lymphoma Type | Cell Markers & Translocation | Histopathology & Clinical Presentation | Prognosis & First-Line Treatment |
|---|---|---|---|
| Hodgkin: Nodular Sclerosis (#1 — 70%) | CD15+, CD30+ Reed-Sternberg variants (Lacunar cells — retraction artifact creates clear space around cell); EBV negative | Young adult females; presents with painless cervical/supraclavicular lymphadenopathy + Anterior Mediastinal Mass; broad collagen bands divide node into nodules | Excellent prognosis; ABVD chemotherapy (Adriamycin [Doxorubicin], Bleomycin, Vinblastine, Dacarbazine) |
| Hodgkin: Mixed Cellularity (#2 — 20%) | CD15+, CD30+ classic Reed-Sternberg cells; strongly EBV-associated (70%, especially in HIV/immunocompromised) | Older men or HIV patients; abundant classic RS cells in a background rich in eosinophils (RS cells secrete IL-5!), plasma cells, and histiocytes | Intermediate prognosis; ABVD regimen |
| Hodgkin: Lymphocyte-Rich vs. Lymphocyte-Depleted | CD15+, CD30+ (Note: Nodular Lymphocyte-Predominant HL is an exception that is CD20+, CD45+, CD15-, CD30- with 'Popcorn' [LP] cells!) | Lymphocyte-Rich has the BEST prognosis. Lymphocyte-Depleted (elderly, HIV+, nearly 100% EBV+) has abundant RS cells, paucity of lymphocytes, and the WORST prognosis | ABVD (or Rituximab + chemo for CD20+ NLPHL) |
| NHL: Diffuse Large B-Cell Lymphoma (DLBCL) | Mature B cell (CD19+, CD20+); mutations in BCL6, BCL2, or c-MYC ('double-hit' lymphoma) | #1 Most Common Non-Hodgkin Lymphoma in Adults! Aggressive, rapidly enlarging nodal or extranodal mass (Waldeyer ring, GI tract, CNS in HIV); arises de novo or via transformation from Follicular Lymphoma or CLL (Richter) | Aggressive but curable (~60–70%) with R-CHOP (Rituximab, Cyclophosphamide, Hydroxydaunorubicin [Doxorubicin], Oncovin [Vincristine], Prednisone) |
| NHL: Follicular Lymphoma | Mature B cell (CD19+, CD20+, CD10+, BCL6+) with t(14;18) translocation | #1 Most Common Indolent (Low-Grade) NHL in Adults. t(14;18) places the anti-apoptotic BCL2 gene (Chr 18) under the constitutively active Ig Heavy Chain enhancer (Chr 14), preventing cytochrome c release. Presents with painless 'waxing and waning' lymphadenopathy; node biopsy shows crowded follicles lacking tingible-body macrophages | Indolent, incurable course; Rituximab (anti-CD20) + Bendamustine or R-CHOP when symptomatic |
| NHL: Mantle Cell Lymphoma | Mature B cell (CD19+, CD20+, CD5+, CD23 NEGATIVE!) with t(11;14) translocation | t(11;14) fuses Cyclin D1 (BCL1 on Chr 11) to the Ig Heavy Chain locus (Chr 14), phosphorylating Rb to drive unchecked G1-to-S cell cycle progression. Older males with disseminated lymphadenopathy, splenomegaly, and GI tract 'lymphomatoid polyposis' | Aggressive, poor prognosis; BTK inhibitors (Ibrutinib/Acalabrutinib) + R-CHOP / cytarabine + autologous stem cell transplant |
| NHL: Burkitt Lymphoma | Mature B cell (CD19+, CD20+, CD10+, Ki-67 ~100%) with t(8;14) translocation | t(8;14) translocates the proto-oncogene c-MYC (Chr 8) to the Ig Heavy Chain locus (Chr 14). Endemic (African): 100% EBV+, presents as a mandibular / jaw mass. Sporadic (Western): presents as an ileocecal / abdominal/pelvic mass in children/young adults. Biopsy: 'Starry-Sky' appearance (sheets of dark lymphocytes interspersed with pale tingible-body macrophages phagocytosing apoptotic debris) | Fastest-growing human tumor (very high risk of Tumor Lysis Syndrome!); highly curable with intensive multi-agent chemo + Rituximab + TLS prophylaxis |
| NHL: Marginal Zone (MALT) Lymphoma | Post-germinal center marginal zone B cells (CD19+, CD20+, CD5-, CD10-); often t(11;18) | Driven by chronic antigen/autoimmune stimulation: Gastric MALToma = Helicobacter pylori; Salivary gland MALToma = Sjögren syndrome; Thyroid MALToma = Hashimoto thyroiditis | Early-stage Gastric MALToma is CURED by H. pylori antibiotic eradication therapy alone (unless t(11;18) is present)! |
Ann Arbor Staging of Lymphoma & Classic 'B Symptoms'
Both Hodgkin and Non-Hodgkin lymphomas are staged using the Ann Arbor Classification based on the anatomic relationship to the diaphragm on FDG-PET/CT: Stage I = involvement of a single lymph node region; Stage II = 2 or more lymph node regions on the SAME side of the diaphragm; Stage III = lymph node regions on BOTH sides of the diaphragm (including the spleen = IIIS); and Stage IV = diffuse or disseminated involvement of one or more extralymphatic organs (e.g., bone marrow, liver, lungs). Each stage is subclassified as 'A' (absence) or 'B' (presence) of systemic Constitutional 'B Symptoms' (driven by TNF-α, IL-1, and IL-6): (1) Unexplained fever > 38°C (100.4°F) (in Hodgkin Lymphoma, classic cyclical fevers lasting 1–2 weeks alternating with afebrile periods are called Pel-Ebstein fevers); (2) Drenching night sweats; and (3) Unintentional weight loss > 10% of body weight over 6 months. A unique board pearl for Hodgkin Lymphoma is acute pain in the involved lymph node immediately after drinking alcohol!
CD5+ B-Cell Neoplasm Differential: CLL vs. Mantle Cell Lymphoma
Normal B lymphocytes are CD19+ and CD20+, whereas CD5 is normally a pan-T-cell marker. Only two B-cell malignancies aberrantly co-express CD20+ and CD5+: Chronic Lymphocytic Leukemia (CLL) and Mantle Cell Lymphoma (MCL). How do you distinguish them on flow cytometry and cytogenetics? CLL is CD23 POSITIVE, shows smudge cells, and has an indolent course, whereas Mantle Cell Lymphoma is CD23 NEGATIVE, Cyclin D1 POSITIVE, harbors t(11;14), and follows an aggressive clinical course!
Long-Term Survivorship Toxicities of Hodgkin Lymphoma Therapy (ABVD & Radiation)
Because young adults with Hodgkin Lymphoma achieve > 85–90% cure rates with ABVD chemotherapy (Adriamycin [Doxorubicin], Bleomycin, Vinblastine, Dacarbazine) and mediastinal radiation, COMLEX Level 2/3 vignettes frequently test long-term survivorship complications 10–20 years later: (1) Doxorubicin (Adriamycin): dose-dependent dilated cardiomyopathy via iron-mediated free radical myocardial damage (prevented by Dexrazoxane); (2) Bleomycin: pulmonary fibrosis (restrictive lung disease with decreased DLCO) and flagellate skin hyperpigmentation; (3) Vinblastine: bone marrow suppression (unlike Vincristine, which causes peripheral neuropathy!); and (4) Mantle/Mediastinal Radiation: markedly increased risk of secondary Breast Cancer (begin annual screening mammography + breast MRI 8 years after chest radiation or at age 25, whichever is LATER!), premature Coronary Artery Disease / constrictive pericarditis, Hypothyroidism (check annual TSH), and treatment-related AML/MDS.
Plasma Cell Dyscrasias: Multiple Myeloma, MGUS & Waldenström Macroglobulinemia
Plasma cell dyscrasias are monoclonal proliferations of terminally differentiated B lymphocytes that secrete a single homogeneous immunoglobulin (M-protein / paraprotein spike on serum or urine protein electrophoresis [SPEP/UPEP]) or free light chains (κ or λ). In Multiple Myeloma (median age ~68 years, twice as common in African Americans), malignant plasma cells proliferate inside the bone marrow and secrete IL-6 (their primary autocrine/paracrine growth factor) and RANKL, stimulating osteoclasts to resorb bone while inhibiting osteoblasts—producing the classic CRAB tetrad.
| Disorder | Diagnostic Criteria (M-Protein & Marrow %) | Immunoglobulin Isotype & Pathophysiology | Clinical Features & Management |
|---|---|---|---|
| Monoclonal Gammopathy of Undetermined Significance (MGUS) | Serum M-protein < 3 g/dL AND < 10% clonal bone marrow plasma cells AND NO CRAB features | IgG, IgA, or IgM paraprotein without end-organ damage | Completely asymptomatic! Present in ~3–5% of adults > 50 yrs; progresses to Multiple Myeloma (or Waldenström if IgM) at a constant rate of 1% per year. Rx: Annual observation only (NO chemo!) |
| Smoldering Multiple Myeloma | Serum M-protein ≥ 3 g/dL OR 10–59% clonal bone marrow plasma cells, WITHOUT CRAB features | IgG or IgA paraprotein | Asymptomatic intermediate stage (~10% per year progression risk over first 5 years). Rx: close surveillance (or lenalidomide in high-risk cases) |
| Multiple Myeloma (MM) | ≥ 10% clonal bone marrow plasma cells (with eccentric 'Clock-Face' chromatin, perinuclear Hof, and Russell/Dutcher bodies) + CRAB end-organ damage (or ≥ 60% plasma cells) | IgG (#1 — 55%) or IgA (#2 — 25%) M-spike on SPEP + monoclonal free κ or λ light chains (Bence Jones proteins) on 24-hr UPEP (note: routine urine dipstick detects only albumin and is FALSE-NEGATIVE for Bence Jones light chains!) | Calcemia (> 11 mg/dL → constipation, stones, confusion), Renal insufficiency (cast nephropathy, AL amyloidosis, Type II proximal RTA / Fanconi syndrome), Anemia (Rouleaux formation, ESR > 100), Bone punched-out lytic lesions (skull, vertebrae → back pain!). Rx: Bortezomib (proteasome inhibitor) + Lenalidomide + Dexamethasone + Daratumumab (anti-CD38) → Autologous HSCT |
| Waldenström Macroglobulinemia (Lymphoplasmacytic Lymphoma) | ≥ 10% bone marrow lymphoplasmacytic infiltrate + Monoclonal IgM M-spike; > 90% harbor MYD88 L265P mutation! | Giant pentameric IgM macromolecules remain trapped intravascularly, drastically increasing serum viscosity | NO lytic bone lesions and NO hypercalcemia! Instead presents with Hyperviscosity Syndrome (headache, blurry vision, 'sausage-link' dilated retinal veins, mucosal bleeding, Raynaud, Cold Agglutinin hemolysis) + hepatosplenomegaly & lymphadenopathy. Rx: Emergent Plasmapheresis for hyperviscosity + Rituximab / Ibrutinib |
Why Multiple Myeloma Causes Infection (#1 Cause of Death) Despite Elevated Total Serum Protein
A classic laboratory hallmark of Multiple Myeloma is an elevated Total Protein with a normal or low Albumin (creating an elevated 'Protein Gap' [Total Protein minus Albumin > 4 g/dL]) and a DECREASED Anion Gap (because positively charged IgG paraproteins act as unmeasured cations!). However, despite massive overproduction of a single useless monoclonal IgG or IgA paraprotein, normal polyclonal B-cell differentiation is severely suppressed ('immunoparesis'), resulting in functional hypogammaglobulinemia and recurrent bacterial pneumonia and pyelonephritis with encapsulated organisms (Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, E. coli)—making infection the #1 cause of mortality in Multiple Myeloma!
Primary AL Amyloidosis & Myeloma Kidney (Light Chain Cast Nephropathy)
Multiple Myeloma damages the kidney via two distinct mechanisms: (1) Myeloma Cast Nephropathy ('Myeloma Kidney'): excess filtered free κ or λ light chains (Bence Jones proteins) overwhelm proximal tubular endocytosis (frequently causing acquired Fanconi syndrome / Type II proximal RTA) and reach the distal tubule, where they bind Tamm-Horsfall mucoprotein (uromodulin) to form large, obstructing waxy eosinophilic casts surrounded by multinucleated giant cells; and (2) Primary AL (Light-Chain) Amyloidosis: misfolded monoclonal light chains (most commonly λ light chains) deposit extracellularly in β-pleated sheets that stain apple-green birefringent under polarized light with Congo red, causing nephrotic syndrome, restrictive cardiomyopathy, hepatomegaly, macroglossia (enlarged tongue), and bilateral periorbital purpura ('raccoon eyes' after minor trauma/proctoscopy).
Langerhans Cell Histiocytosis (Birbeck Granules) in Pediatric Lytic Bone Lesions
When a child or infant (rather than an older adult) presents with punched-out lytic skull bone lesions, diabetes insipidus (pituitary stalk infiltration), exophthalmos, and a seborrheic mastoid/scalp rash (Hand-Schüller-Christian / Letterer-Siwe spectrum), the diagnosis is Langerhans Cell Histiocytosis (LCH)—a clonal neoplastic proliferation of immature dendritic Langerhans cells (frequently harboring BRAF V600E). Biopsy is pathognomonic: cells express CD1a+, S100+, and Langerin (CD207)+, and electron microscopy reveals tennis-racket-shaped cytoplasmic Birbeck granules!
Oncologic Emergencies: Tumor Lysis Syndrome, Hypercalcemia, Febrile Neutropenia & Cord Compression
Rapid recognition and algorithmic stabilization of acute oncologic emergencies is tested across Internal Medicine, Pediatrics, and Emergency Medicine shelf exams. Whenever cytotoxic chemotherapy or corticosteroids are initiated in a patient with a high-turnover, bulky hematologic malignancy (Burkitt Lymphoma, Acute Lymphoblastic Leukemia, AML with WBC > 100,000/μL, or DLBCL), massive synchronous lysis of tumor cells dumps intracellular ions and nucleic acids directly into the systemic circulation, triggering Tumor Lysis Syndrome (TLS).
| Oncologic Emergency | Pathophysiologic Mechanism & Classic Culprits | Diagnostic Presentation & Labs | Immediate First-Line Stabilization Protocol |
|---|---|---|---|
| Tumor Lysis Syndrome (TLS) | Massive tumor cell lysis after chemo (Burkitt lymphoma, ALL, AML) releases intracellular K+, PO43-, and purine nucleic acids (hypoxanthine → xanthine → uric acid via xanthine oxidase) | 3 HIGH, 1 LOW: • HIGH Potassium (> 6 mEq/L) → lethal arrhythmias • HIGH Phosphate (> 4.5 mg/dL) • HIGH Uric Acid (> 8 mg/dL) → renal tubular uric acid crystal AKI • LOW Calcium (< 7 mg/dL) (CaPO4 precipitation → tetany/QTc prolongation!) | Prophylaxis: Aggressive IV Isotonic Crystalloid Hydration + Allopurinol or Febuxostat. Active TLS / Uric Acid > 8: IV Hydration + Rasburicase (recombinant urate oxidase; contraindicated in G6PD deficiency!) + treat hyperkalemia |
| Neutropenic Fever | Chemotherapy-induced mucosal barrier breakdown + Absolute Neutrophil Count (ANC) < 500 cells/μL (or < 1,000 expected to fall < 500 in 48h) | Single oral temperature ≥ 38.3°C (101°F) or ≥ 38.0°C (100.4°F) sustained for ≥ 1 hour. #1 bacteremia = Gram+ cocci; most rapidly lethal = Pseudomonas aeruginosa! | Obtain 2 sets of blood cultures (peripheral + central line) and administer IV anti-pseudomonal beta-lactam monotherapy WITHIN 60 MINUTES: Cefepime, Meropenem, or Piperacillin-Tazobactam. Add Vancomycin ONLY if catheter infection, skin/cellulitis, pneumonia, or hemodynamic shock. Add Amphotericin B / Voriconazole / Caspofungin if fever persists > 4–7 days! |
| Hypercalcemia of Malignancy | 1. PTHrP secretion (Squamous cell lung, Renal, Breast, Bladder cancer). 2. Osteolytic metastases / RANKL (Multiple Myeloma, Breast). 3. 1α-hydroxylase calcitriol overproduction (Hodgkin/Non-Hodgkin Lymphoma!) | Serum Ca2+ > 14 mg/dL (or symptomatic > 12 mg/dL): polyuria/nephrogenic DI (profound dehydration!), constipation, bone pain, confusion/stupor, shortened QT interval; PTH is SUPPRESSED | Step 1 (Immediate, works in hours): Aggressive IV 0.9% Normal Saline Hydration (200–300 mL/hr) + Subcutaneous Calcitonin (works in 4–6h, tachyphylaxis by 48h). Step 2 (Sustained, takes 2–4 days): IV Zoledronic Acid or Pamidronate (or Denosumab if renal failure; add corticosteroids if lymphoma calcitriol-mediated!) |
| Malignant Spinal Cord Compression (MSCC) | Epidural metastasis from Prostate, Breast, Lung cancer, or Multiple Myeloma/Lymphoma (Thoracic spine #1 [65%] > Lumbosacral > Cervical) | Progressive back pain (worse when supine/at night or with Valsalva!) → symmetric lower extremity UMN weakness, sensory level, and urinary retention/overflow incontinence | Step 1 (First Action!): Give Immediate High-Dose IV Dexamethasone (10 mg bolus) FIRST—even BEFORE the MRI is completed! Step 2: Emergent Whole-Spine MRI with contrast + neurosurgical decompression or emergent radiation therapy |
| Superior Vena Cava (SVC) Syndrome | Extrinsic compression of thin-walled SVC by Small Cell or Squamous Cell Lung Cancer (#1 in adults) or Non-Hodgkin / T-ALL Mediastinal Lymphoma (#1 in young adults/children) | Facial/neck swelling ('collar of Stokes'), facial plethora, distended non-pulsatile neck and chest wall veins, upper extremity edema, dyspnea, headache; Pemberton sign (facial cyanosis/plethora when raising both arms above head) | Elevate head of bed; CT Chest with IV contrast + obtain tissue biopsy BEFORE starting steroids/radiation (unless stridor, laryngeal edema, or cerebral edema/coma requires emergent endovascular SVC stenting + radiation!) |
Why Loop Diuretics (Furosemide) Are NO LONGER Routine in Hypercalcemia of Malignancy
A classic NBME/COMLEX clinical update: patients with severe hypercalcemia of malignancy are profoundly intravascularly volume-depleted because hypercalcemia activates calcium-sensing receptors in the thick ascending limb and downregulates aquaporin-2 channels in the collecting duct—inducing nephrogenic diabetes insipidus (polyuria) and vomiting. Therefore, the #1 immediate first step in severe hypercalcemia is aggressive IV 0.9% Normal Saline resuscitation to restore GFR and promote calciuria. Loop diuretics (furosemide) should NOT be given routinely unless the patient develops iatrogenic volume overload / heart failure after saline resuscitation, because premature furosemide worsens intravascular depletion and renal calcium reabsorption!
Excisional Lymph Node Biopsy vs. Fine-Needle Aspiration (FNA) in Suspected Lymphoma
When a patient presents with persistent, painless, firm supraclavicular or cervical lymphadenopathy (> 2 cm for > 4 weeks) accompanied by B symptoms, what is the single best diagnostic test? Excisional Biopsy of an intact lymph node! NEVER choose Fine-Needle Aspiration (FNA) as the definitive diagnostic test for Hodgkin or Non-Hodgkin Lymphoma, because distinguishing nodular sclerosis vs. follicular vs. diffuse architecture (and identifying scattered Reed-Sternberg cells) requires evaluating the intact histological architecture of the entire lymph node.
Hyperleukocytosis & Leukostasis Syndrome (WBC > 100,000/uL in AML vs. CLL)
When a patient with Acute Myeloid Leukemia (AML) or CML Blast Crisis presents with a peripheral WBC count > 100,000/μL accompanied by dyspnea/hypoxemia (pulmonary capillary sludging), blurry vision/retinal hemorrhages, headache, confusion, focal neurologic deficits, or priapism, the diagnosis is Symptomatic Hyperleukocytosis / Leukostasis. Why does leukostasis occur at lower WBC counts in AML than in CLL? Because myeloblasts are large, rigid, non-deformable cells that express endothelial adhesion molecules and secrete inflammatory cytokines, plugging the pulmonary and cerebral microvasculature! Treat immediately with emergent Cytoreduction (Induction Chemotherapy or Hydroxyurea) + IV Hydration + Leukapheresis (and avoid packed RBC transfusions until the blast count is lowered, as RBC transfusions acutely spike whole-blood viscosity!).
COMLEX / OMM Integration
NBOME High-Yield Correlate
OMM & Lymphatic Pump Contraindications in Hematologic Malignancies, Bone Metastases & Splenomegaly
Hematologic malignancies carry high-yield, heavily tested absolute and relative contraindications to Osteopathic Manipulative Treatment (OMT). First, in Multiple Myeloma (or metastatic bone disease), punched-out osteolytic bone lesions (driven by RANKL upregulation and IL-6 osteoclastic activation) create extreme cortical fragility; therefore, High-Velocity Low-Amplitude (HVLA) thrust techniques and vigorous articulatory/springing maneuvers are ABSOLUTELY CONTRAINDICATED over the spine and ribs due to the risk of catastrophic pathologic vertebral fracture and acute spinal cord compression. Second, in patients with massive splenomegaly from Chronic Myeloid Leukemia (CML), Primary Myelofibrosis, Hairy Cell Leukemia, or Chronic Lymphocytic Leukemia (CLL), direct splenic pump techniques and vigorous left lower rib cage compression are contraindicated due to the risk of life-threatening splenic rupture and hemoperitoneum. Third, whether lymphatic pump techniques (thoracic pump, pedal pump) are safe in active lymphoma or leukemia is a classic board ethics/biomechanics question: while gentle myofascial release, counterstrain, and cranial techniques are safe for palliative pain relief, direct manipulation over a malignant lymphomatous mass is contraindicated. Furthermore, in patients with severe thrombocytopenia (platelets < 20,000–50,000/μL) or APL-induced DIC, deep tissue massage and HVLA are contraindicated due to risk of retroperitoneal or epidural hematoma.
Board Traps & Common Distractors
- Trap: Waiting for bone marrow cytogenetics or FISH confirmation of t(15;17) before administering All-Trans Retinoic Acid (ATRA) in a patient presenting with blasts containing Auer rods, mucocutaneous bleeding, and laboratory evidence of DIC (low fibrinogen, elevated D-dimer, prolonged PT/PTT). Give ATRA immediately upon clinical suspicion of Acute Promyelocytic Leukemia (APL) to force promyelocyte differentiation and halt fatal DIC!
- Trap: Administering Rasburicase for Tumor Lysis Syndrome in a patient with known or suspected G6PD Deficiency. Because Rasburicase oxidizes uric acid into allantoin and generates hydrogen peroxide (H2O2) as a direct byproduct, it precipitates fulminant intravascular hemolysis and methemoglobinemia in G6PD-deficient patients!
- Trap: Ordering a Technetium-99mradionuclide bone scan (scintigraphy) to stage osteolytic bone lesions in Multiple Myeloma. Because Tc-99m methylene diphosphonate measures osteoblastic bone remodeling and Multiple Myeloma purely activates osteoclasts (via RANKL) while inhibiting osteoblasts (via DKK1), myeloma lytic lesions appear FALSE-NEGATIVE ('cold') on routine bone scans! Order a whole-body low-dose CT, FDG-PET/CT, or plain radiograph skeletal survey instead.
- Trap: Administering IV iodinated contrast dye for a CT scan in a patient with Multiple Myeloma and elevated serum creatinine. Iodinated radiocontrast complexes with Tamm-Horsfall mucoprotein and monoclonal light chains (Bence Jones proteins) in the distal nephron, precipitating acute oliguric renal failure (myeloma cast nephropathy)!
- Trap: Confusing a septic Leukemoid Reaction (WBC > 50,000/μL due to severe infection) with Chronic Myeloid Leukemia (CML). A leukemoid reaction demonstrates a HIGH Leukocyte Alkaline Phosphatase (LAP) score, toxic granulations, Döhle bodies, and NO basophilia or t(9;22), whereas CML has a LOW LAP score, prominent basophilia/eosinophilia, splenomegaly, and the Philadelphia chromosome t(9;22) BCR-ABL1!
- Trap: Treating asymptomatic early-stage Chronic Lymphocytic Leukemia (Rai stage 0 / Binet stage A) or Smoldering Multiple Myeloma / MGUS with immediate cytotoxic chemotherapy. Early asymptomatic CLL and MGUS/smoldering myeloma have no survival benefit from immediate chemotherapy and are managed with active surveillance ('watch and wait') until symptomatic cytopenias, bulky lymphadenopathy, or CRAB end-organ damage develops!
- Trap: Failing to recognize ATRA Differentiation Syndrome (formerly Retinoic Acid Syndrome) 2–21 days after starting ATRA or arsenic trioxide for APL. When an APL patient develops unexplained fever, dyspnea, pulmonary infiltrates, pleural/pericardial effusions, hypotension, and weight gain from massive cytokine release by maturing myeloid cells, immediately administer IV Dexamethasone (10 mg BID)!
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Volume 2: Organ System Clinical Pathology • Chapter 16 of 60