PA H7 | Benign Leukocytosis & Leukemias — Glossary

An absolute neutrophil count < 0.5 × 10⁹/L causing extreme vulnerability to life-threatening infection; most commonly drug-induced (idiosyncratic or dose-related).

A variant of acute leukaemia where blasts are confined to the marrow and absent from peripheral blood, presenting solely as pancytopaenia; diagnosis requires bone marrow biopsy.

Itching triggered by contact with water at any temperature; a characteristic symptom of polycythaemia vera, caused by histamine release from increased skin mast cells and basophils.

A vitamin A derivative that binds the PML-RARα fusion protein in APL, reversing maturation arrest and causing promyelocytes to differentiate; transforms APL from the most lethal to the most curable AML.

Large lymphocytes with abundant pale-blue cytoplasm and lobulated nuclei moulding around adjacent red cells, seen in EBV infectious mononucleosis; they are reactive CD8+ T cells, not infected cells.

Pathognomonic needle-like pink cytoplasmic inclusion in AML blasts, formed by crystallised fused primary (azurophilic) granules; their presence excludes ALL.

Haemolysis caused by autoantibodies (usually warm IgG) against red cell surface antigens; a common complication of CLL, diagnosed by a positive direct Coombs (antiglobulin) test.

An absolute basophil count > 0.1 × 10⁹/L; almost always indicates a myeloproliferative neoplasm, most classically CML.

A fusion oncogene created by the t(9;22) translocation; encodes a constitutively active tyrosine kinase that drives uncontrolled myeloid proliferation in CML.

A three-stage (A/B/C) CLL staging system based on number of involved lymphoid areas and presence of anaemia/thrombocytopenia; simpler than Rai and used in Europe.

An immature, undifferentiated haematopoietic precursor cell with high nuclear-to-cytoplasmic ratio, fine chromatin, and prominent nucleoli; the hallmark cell type in acute leukaemia.

The terminal phase of CML in which ≥20% blasts appear in blood or bone marrow; equivalent to transformation to acute leukaemia (AML or ALL) and carries a very poor prognosis.

Common acute lymphoblastic leukaemia antigen; expressed on early B-cell precursors and a key flow cytometry marker for B-ALL.

A clonal proliferation of mature, immunologically incompetent B lymphocytes (CD5+/CD19+/CD23+); the commonest leukaemia in the Western elderly population.

The acquisition of additional genetic mutations within a pre-existing malignant clone, leading to a more aggressive phenotype; seen in CML (blast crisis) and CLL (Richter transformation).

Teardrop-shaped red blood cells; a characteristic finding in primary myelofibrosis, caused by distortion of red cells as they exit a fibrotic bone marrow.

The release of neutrophils from the marginating pool (adherent to vessel walls) into the circulating pool, producing a rapid but transient rise in WBC count without increased marrow production.

A consumptive coagulopathy where widespread intravascular coagulation consumes clotting factors and platelets, causing simultaneous bleeding and thrombosis; classically triggered by APL.

Small pale-blue cytoplasmic inclusions in neutrophils composed of rough endoplasmic reticulum remnants; accompany toxic granulation in severe systemic illness.

An absolute eosinophil count > 0.4 × 10⁹/L; major causes remembered as NAACP (Neoplastic, Allergic, Addison's, Collagen vascular, Parasites) plus drugs.

A chronic myeloproliferative neoplasm characterised by sustained platelet count elevation due to clonal megakaryocyte proliferation; associated with JAK2 V617F and presenting with thrombosis and bleeding.

Fusion gene from t(12;21) in B-ALL; the commonest chromosomal translocation in childhood ALL; cryptic by standard karyotype (needs FISH); confers excellent prognosis.

A blast in acute promyelocytic leukaemia (M3) containing bundles of multiple Auer rods, resembling a bundle of sticks; associated with t(15;17) and DIC risk.

An internal tandem duplication mutation in the FLT3 receptor tyrosine kinase gene; acts as a Class I proliferation-driving mutation in AML; associated with poor prognosis; targeted by midostaurin.

Gingival infiltration by monocytic blasts in FAB M4/M5 AML, causing swollen, spongy, haemorrhagic gums; a clinical clue to monocytic AML lineage.

IgM antibodies produced in EBV infectious mononucleosis that agglutinate sheep and horse red blood cells; detected by the monospot (Paul-Bunnell) test.

A karyotype with >50 chromosomes per blast cell; found in ~25% of childhood B-ALL and confers excellent prognosis through increased sensitivity to antimetabolite chemotherapy.

Reduced levels of immunoglobulins in blood; occurs in CLL because the accumulated neoplastic B cells are non-functional and fail to produce adequate antibodies, leading to recurrent bacterial infections.

The first-generation BCR-ABL1 tyrosine kinase inhibitor (TKI) used as first-line therapy in CML; competes with ATP at the kinase domain, blocking oncogenic signalling.

A clinical syndrome caused by primary EBV infection, characterised by fever, pharyngitis, lymphadenopathy, splenomegaly, and atypical lymphocytosis; diagnosed by monospot (heterophile antibody) test.

A gain-of-function point mutation in the Janus kinase 2 gene; the predominant molecular driver in polycythaemia vera (>95%), essential thrombocythaemia (~60%), and primary myelofibrosis (~60%).

Leucocyte alkaline phosphatase score — a cytochemical measure of alkaline phosphatase in neutrophils scored on 100 cells (0–400); high in reactive states, near zero in CML.

The appearance of immature granulocytes (band neutrophils, metamyelocytes, myelocytes) in the peripheral blood, indicating accelerated marrow release, usually in response to severe infection or inflammation.

An increase in the total white cell count above 11 × 10⁹/L; requires differential count interpretation to identify the responsible cell line and mechanism.

A decrease in total white cell count below 4.0 × 10⁹/L, most commonly due to neutropenia; significantly impairs innate immune defence.

A clonal malignant proliferation of haematopoietic progenitor cells originating in the bone marrow, characterised by accumulation of abnormal cells in marrow, blood, and organs.

A reactive leucocytosis (often > 50 × 10⁹/L) with a left shift that mimics leukaemia; distinguished from CML by a high LAP score, absence of basophilia, and an identifiable trigger.

A peripheral blood finding combining blasts, nucleated red blood cells, and immature myeloid cells, reflecting marrow replacement by infiltrative disease.

The simultaneous presence of immature granulocytes and nucleated red blood cells in peripheral blood, indicating bone marrow infiltration or displacement.

An absolute lymphocyte count exceeding 4.8 × 10⁹/L in adults; may be reactive (viral, bacterial) or neoplastic (CLL, lymphoma) — morphology and clonality distinguish the two.

The central pathological event in acute leukaemia: a somatic mutation blocks haematopoietic progenitors at an immature blast stage, preventing their differentiation into functional blood cells.

An absolute monocyte count > 1.0 × 10⁹/L; characteristically associated with chronic granulomatous infections (TB), autoimmune disease, and chronic myelomonocytic leukaemia.

An enzyme in primary myeloid granules used as a cytochemical marker (brown staining, ≥3% blasts positive) to confirm myeloid lineage in AML; absent in ALL.

A memory aid for causes of eosinophilia: Neoplastic, Allergic, Addison's disease, Collagen vascular disease, Parasites (tissue-invasive helminths).

An absolute neutrophil count exceeding 7.5 × 10⁹/L, most commonly caused by bacterial infection, inflammation, or corticosteroid therapy.

A common somatic mutation in AML (cytoplasmic mislocalisation of nucleophosmin); associated with normal karyotype AML and favourable prognosis when FLT3-ITD is absent.

A reciprocal translocation t(9;22) creating the BCR-ABL fusion oncogene; pathognomonic of CML and absent in leukaemoid reactions.

The fusion protein produced by t(15;17) in APL; it blocks myeloid differentiation at the promyelocyte stage. ATRA binds and degrades this fusion protein, restoring differentiation.

A chronic myeloproliferative neoplasm characterised by clonal erythroid proliferation, raised haematocrit, and risk of thrombosis; associated with JAK2 V617F and presenting with aquagenic pruritus.

A chronic myeloproliferative neoplasm characterised by clonal myeloid proliferation with reactive marrow fibrosis, massive splenomegaly, and a leucoerythroblastic blood picture with teardrop cells.

A five-stage (0-IV) CLL staging system based on lymphocytosis, lymphadenopathy, organomegaly, anaemia, and thrombocytopenia; used primarily in the USA.

Recombinant urate oxidase that converts uric acid to the more soluble allantoin; used for prophylaxis and treatment of hyperuricaemia in tumour lysis syndrome.

The transformation of CLL into an aggressive large B-cell lymphoma (DLBCL) in approximately 5-10% of cases; presents with rapid lymph node enlargement, high LDH, and constitutional symptoms; median survival <1 year.

An anatomical compartment shielded from systemic chemotherapy by a physiological barrier (blood-brain barrier for CNS; blood-testis barrier for testis); in ALL, these sites require specific prophylactic therapy.

Also called smear cells or Gumprecht shadows; crushed lymphocyte remnants visible on blood films in CLL, resulting from the mechanical fragility of neoplastic B lymphocytes during smear preparation; pathognomonic of CLL.

A nuclear enzyme expressed in lymphoid progenitors (B and T) and detected by immunostaining; its positivity is a key marker for ALL and distinguishes lymphoblasts from myeloblasts.

Abnormally prominent, dark-staining primary (azurophil) granules in neutrophil cytoplasm, seen in severe sepsis and burns; a morphological marker of reactive, stressed granulopoiesis.

A metabolic emergency from rapid blast destruction releasing intracellular contents, causing hyperkalaemia, hyperphosphataemia, hyperuricaemia, hypocalcaemia, and acute kidney injury.

An enzyme that phosphorylates tyrosine residues on target proteins; when constitutively active (always on), it drives continuous cell proliferation and survival.