Large Granular Lymphocytic Leukemia

Slide 1 · Large Granular Lymphocytic Leukemia

Disease biology • Morphology • Diagnostic integration • Clinicopathologic relevance

A mature cytotoxic lymphocyte neoplasm

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

Recognize the cytologic and tissue features of LGL leukemia.

Explain STAT3 activation and the paradox of severe cytopenias with limited infiltration.

Distinguish T-cell and NK-cell disease using immunophenotype and lineage-aware testing.

Integrate neutropenia, anemia, rheumatologic disease, and relevant mimics.

Slide 3 · A low-grade leukemia with major clinical consequences

Clonal cytotoxic

Lymphocytes

Three defining features

An adult-predominant mature lymphoid proliferation

T-cell and NK-cell lineages are recognized

Cytopenias and autoimmunity may be prominent

Slide 4 · Where this disease fits

Mature lymphoid neoplasms

Peripheral T / NK cell lineage

Large granular lymphocytic leukemia

In contrast to rapidly growing lymphoid tumors, a relatively low burden of infiltrating cells can coexist with clinically important cytopenia.

Slide 5 · Normal large granular lymphocytes have a cytotoxic role

Cytotoxic lymphocyte

Cytoplasmic granules

Target-cell killing

“Large granular lymphocyte” describes morphology; Benign activated cytotoxic lymphocytes may also appear granular.

Slide 6 · Reactive expansion is not automatically leukemia

Reactive granular lymphocytes

LGL leukemia

Expansion may follow immune stimulation

Sustained cytotoxic-cell population

Often polyclonal and transient

Often demonstrable clonal restriction

Interpret in its clinical context

Link clone to symptoms and cytopenia

Slide 7 · Two major lineages

T-cell LGL leukemia

NK-cell LGL leukemia

Derived from mature T cells

Derived from NK cells

Surface CD3 positive

Surface CD3 negative

Often has lymphocytosis and splenomegaly

Can have minimal lymphocytosis or splenic enlargement

Slide 8 · Typical age and clinical tempo

Both recognized forms occur mainly in adults.

The textbook characterizes the overall proliferation as uncommon.

Clinical presentation ranges from subtle detection to symptomatic cytopenias.

Slide 9 · The presenting phenotype can be recognized clinically

Neutropenia

Anemia

Autoimmune

Manifestations

Slide 10 · Typical T-cell presentation

Mild-to-moderate lymphocytosis is common.

Splenomegaly is a characteristic associated finding.

The dominant clinical threat may still be neutropenia or anemia.

Slide 11 · NK-cell disease can be difficult to detect clinically

Peripheral lymphocyte count may show little or no elevation.

Splenomegaly may be minimal or absent.

A normal or only mildly elevated lymphocyte count does not eliminate suspicion.

Slide 12 · Findings that are present versus commonly absent

Commonly encountered

Often absent

Neutropenia / anemia

Large lymph nodes

Granular cells on smear

Clinically obvious liver enlargement

Splenomegaly in T-cell disease

Marked mass-forming disease

Slide 13 · Why an indolent neoplasm may present abruptly

Small circulating clone

Immune or marrow consequences

Clinically significant cytopenia

A small neoplastic infiltrate does not reliably predict the severity of peripheral blood abnormalities.

Slide 14 · Classic peripheral blood appearance

Large, mature-appearing lymphocyte

Pale blue cytoplasm

Coarse azurophilic granules

Original schematic — not a diagnostic blood smear

Slide 15 · Granules are helpful—but not diagnostic

Granular cytotoxic lymphocyte

Simplified lymphocyte without granules

Schematic comparison; Morphology alone cannot establish lineage or clonality

Slide 16 · How to describe the neoplastic cell

A relatively large, mature-appearing lymphocyte.

Abundant pale-blue cytoplasm.

A small number of coarse azurophilic cytoplasmic granules.

Peripheral blood smear provides the clearest morphologic view.

Slide 17 · What the granules signify

Azurophilic granules are a conspicuous cytotoxic-cell feature.

Their presence supports the LGL morphology.

The smear alone cannot classify the cell as T versus NK or prove neoplasia.

Slide 18 · Blood, marrow, spleen, and liver show different patterns

Peripheral blood

Often conspicuous cytoplasmic granules

Bone marrow

Sparse interstitial cells may be overlooked

Spleen

May be enlarged; Subtle infiltrate

Liver

Sparse infiltrate; Hepatomegaly often absent

Slide 19 · Marrow disease may be deceptively subtle

Sparse interstitial

Infiltrates

The diagnostic paradox

The infiltrate can be difficult to appreciate on routine morphology.

Immunohistochemistry increases visibility of the neoplastic population.

Cytopenia severity may exceed the apparent infiltrative burden.

Slide 20 · Why immunohistochemistry can reveal marrow disease

Scattered neoplastic cells

Low visual contrast on H&E

Lineage-specific immunostaining

This schematic explains detection strategy; It is not a histologic specimen.

Slide 21 · Surface CD3 is the essential lineage fork

T-cell disease

NK-cell disease

Surface CD3 positive

Surface CD3 negative

T-cell markers support lineage

NK markers such as CD56 support lineage

May be tested for TCR clonality

TCR rearrangement is not the appropriate NK clone test

Slide 22 · Typical expanded T- versus NK-phenotypes

T-LGLL

NK-LGLL

CD3+; Often CD8+

Surface CD3−; Often CD16+

CD57 often positive

CD56 may be expressed

TCR clonality assessment

NK repertoire / KIR restriction can support clonality

Slide 23 · Avoid single-marker diagnosis

CD3 determines T-lineage in the standard setting; CD56 alone is not sufficient.

CD8, CD16, CD56, and CD57 patterns have exceptions.

A coherent cytotoxic phenotype must be integrated with morphology and clinical context.

Slide 24 · Physiologic placement of STAT3 downstream of cytokines

Cytokine receptor

Intracellular signaling

STAT3 activation

Transcriptional response

STAT3 functions downstream of cytokine receptors in normal cell signaling.

Slide 25 · STAT3 mutations are recurrent but not universal

Acquired STAT3 mutations in approximately 30%–40% of cases.

The mutations occur in both T-cell and NK-cell forms.

STAT3 is a transcription factor functioning downstream of cytokine receptors.

Slide 26 · Mutant STAT3 can escape cytokine dependence

Cytokine receptor

Intracellular signaling

STAT3 activation

Transcriptional response

Activating STAT3 mutation

Mutant signaling can persist without ordinary cytokine-dependent control.

Slide 27 · How persistent signaling supports cell expansion

Acquired activating lesion

Constitutive STAT3 activity

Survival / expansion of LGL clone

The proposed biological link is supported by recurrent activating lesions; It does not establish the mechanism of each cytopenia.

Slide 28 · A negative STAT3 result does not exclude LGL leukemia

Most cases do not carry a detectable STAT3 mutation estimate.

Molecular findings support—but do not replace—morphology, phenotype, and clonality.

Classifying disease solely by STAT3 mutation status would miss many cases.

Slide 29 · Why molecular evidence must be interpreted cautiously

STAT3 mutation is an acquired supportive lesion, not a universally present marker.

Demonstrating clonality does not by itself establish that a clone causes the cytopenia.

The patient’s clinical and hematologic context remains essential.

Slide 30 · Cytopenias dominate the clinical picture

Neutrophils

Reduced

Erythrocytes

Reduced

Cytopenia-related

Symptoms

Slide 31 · Neutropenia is a defining clinical problem

Neutropenia is frequently more consequential than lymphocytosis.

Reduced mature neutrophils can predispose to bacterial infection.

Possible arrest of granulocyte progenitor maturation.

Slide 32 · One marrow correlate of neutropenia

Granulocyte precursors

Maturation arrest in some cases

Fewer mature neutrophils

Maturation arrest is a possible observation, not a universal biopsy finding.

Slide 33 · Anemia is part of the core disease phenotype

Anemia is one of the dominant hematologic abnormalities.

Fatigue and reduced exercise tolerance may follow diminished oxygen-carrying capacity.

Cell counts alone do not explain the underlying mechanism of every case.

Slide 34 · Pure red cell aplasia is an uncommon association

Pure red cell aplasia may occasionally occur.

The clinical consequence is profound erythroid underproduction.

The marrow finding is distinct from simple replacement by numerous leukemic cells.

Slide 35 · Cytopenia severity need not follow tumor burden

Anatomic finding

Functional outcome

Sparse marrow infiltration

Potentially marked neutropenia

Only limited space occupied by tumor

Anemia and sometimes pure red cell aplasia

No clear mass effect

Clinically important hematologic disease

Slide 36 · Autoimmune mechanisms are plausible, not fully established

LGL neoplastic expansion

Immune dysregulation (proposed)

Cytopenias and rheumatic disease

Robbins explicitly describes the mechanistic basis as uncertain.

Slide 37 · Rheumatologic disease is enriched

Patients have an increased incidence of rheumatologic disorders.

The clinical association raises suspicion of immune dysregulation.

Association does not prove a single causal pathway in each patient.

Slide 38 · Felty syndrome is defined by a clinical triad

Rheumatoid

Arthritis

Splenomegaly

Neutropenia

Slide 39 · Felty syndrome and LGL leukemia can overlap

Some patients presenting with Felty syndrome have underlying LGL leukemia.

The same triad may motivate hematologic evaluation.

Neither rheumatoid arthritis nor splenomegaly alone proves a clonal LGL disorder.

Slide 40 · T-cell and NK-cell presentation patterns

T-cell predominant pattern

NK-cell predominant pattern

May reveal clear lymphocytosis

May have little lymphocytosis

Splenomegaly relatively characteristic

Splenomegaly may be subtle

Generally indolent

Course varies; Must separate aggressive NK leukemia

Slide 41 · When to suspect LGL leukemia clinically

Persistent unexplained neutropenia, with or without anemia.

Rheumatoid arthritis / splenomegaly plus cytopenias.

Granular lymphocytes noted on peripheral smear.

An atypical or persistent cytotoxic lymphocyte population.

Slide 42 · Initial evaluation begins with blood findings

CBC with differential

Peripheral blood morphology

Lineage-directed flow cytometry

Clinical context determines whether further clonality and marrow studies are needed.

Slide 43 · Peripheral blood smear: Interpret with restraint

Check for granular cytoplasm and mature lymphoid appearance.

Estimate whether granular lymphocytes are increased.

Recognize that morphology is suggestive rather than specific.

Slide 44 · Flow cytometry characterizes the lineage

Determine surface CD3 status to separate T and NK patterns.

Use cytotoxic T/NK marker combinations rather than an isolated positive result.

Look for a relatively uniform, aberrant or restricted cell population.

Slide 45 · Demonstrating a T-cell clone

Suspected T-LGLL

Restricted TCR repertoire

Clonality supports diagnosis

T-cell receptor gene rearrangement or repertoire-based assays provide evidence of a persistent clone.

Slide 46 · NK-cell clonality requires different logic

Surface CD3− NK population

KIR restriction and/or molecular evidence

Support NK-LGLL in context

NK cells do not use T-cell receptor rearrangement as a clonality readout.

Slide 47 · A STAT3 mutation is an adjunct, not a shortcut

A mutation strengthens the evidence for an acquired LGL population.

A negative molecular panel does not rule out disease.

Somatic findings must be considered alongside immunophenotype, persistence, and clinical effects.

Slide 48 · When marrow examination adds value

Unexplained or complex cytopenias despite peripheral blood testing.

A need to evaluate alternative marrow pathology.

Suspicion of sparse LGL infiltrates that require immunostaining.

Slide 49 · An integrated diagnostic approach

Clinical trigger

Unexplained cytopenias ± autoimmune disease

Blood assessment

CBC, morphology of LGLs

Lineage characterization

T- vs NK-cell flow cytometry

Evidence of clone

TCR clonality or NK-associated evidence

Integrated conclusion

Clinical + phenotype + clonality; Exclude mimics

Slide 50 · Reactive LGL expansion: The major mimic

Reactive proliferation

LGL leukemia

Often follows an inflammatory or infectious trigger

Persistent clinical and hematologic pattern

Potentially mixed and polyclonal

Evidence of a restricted cytotoxic population

May resolve as stimulus subsides

Continued cytopenias or disease-associated findings

Slide 51 · Do not assume all neutropenia is leukemic

Drug-related, infectious, autoimmune, and other marrow causes may coexist.

A small incidental clone may not explain all hematologic abnormalities.

Assigning causation requires clinicopathologic correlation and appropriate exclusions.

Slide 52 · Distinguish NK-LGLL from aggressive NK-cell leukemia

NK-LGLL

Aggressive NK-cell leukemia

Usually persistent/indolent clinical course

Acute, fulminant systemic presentation

Mature NK phenotype and clone evidence

Systemic organ involvement and atypia

Evaluate chronic cytopenias / NK cells

Urgent distinction due to severe behavior

Slide 53 · Distinguish LGL leukemia from extranodal NK/T lymphoma

LGL leukemia

Extranodal NK/T lymphoma

Usually circulating LGLs / cytopenias

Often destructive extranodal mass

Sparse marrow / organ infiltration

Angiocentric destructive infiltrate

STAT3 alterations in subset

Classically strongly EBV-associated

Slide 54 · WHO-HAEM5 clarifies NK-cell nomenclature

WHO 5th edition uses “NK-large granular lymphocytic leukemia.”

This replaces the older designation “chronic lymphoproliferative disorder of NK cells.”

Aggressive NK-cell leukemia remains a separate, clinically different entity.

Slide 55 · Prognosis is tied to hematologic consequences

The clinical course is variable rather than universally aggressive.

Severity of neutropenia and anemia is a major determinant of morbidity.

The response of cytopenias to treatment influences the clinical course.

Slide 56 · Therapeutic logic

Clinically significant cytopenia

Low-dose systemic therapy / steroids

Assess hematologic response

Response to low-dose chemotherapy or steroids; This slide does not prescribe a regimen.

Slide 57 · Monitoring priorities follow the dominant problem

Track neutrophil count and clinically relevant infections.

Assess hemoglobin and symptoms related to anemia.

Follow the clinical course and tolerance/response to any chosen treatment.

Slide 58 · Case 1 — neutropenia with rheumatoid arthritis

Clinical vignette

An older adult with rheumatoid arthritis has persistent neutropenia and a palpable spleen. The peripheral blood smear shows several mature lymphocytes with coarse azurophilic granules.

What further evidence is needed before calling this LGL leukemia?

Slide 59 · Case 1 — diagnostic reasoning

The Felty triad is present, but it is not by itself a leukemia diagnosis.

Flow cytometry should establish the cytotoxic lineage and phenotype.

TCR clonality or other appropriate clonality assessment supports an LGL neoplasm.

Exclude competing causes of neutropenia.

Slide 60 · Case 2 — subtle NK-cell proliferation

Clinical vignette

An adult is evaluated for persistent anemia and neutropenia. The absolute lymphocyte count is not strikingly elevated. Flow cytometry identifies a uniform surface CD3-negative NK-cell population.

Which additional distinction and tests matter most?

Slide 61 · Case 2 — diagnostic reasoning

Minimal lymphocytosis does not exclude NK-LGLL.

Assess whether the NK population is restricted or otherwise clonal.

Distinguish chronic NK-LGLL from aggressive NK-cell leukemia using clinical tempo and systemic findings.

Slide 62 · Apply the phenotype: T or NK?

Clinical vignette

A persistent granular lymphocyte population is surface CD3-positive, often CD8-positive, and appears restricted by a TCR-based clonality assay. The patient has chronic neutropenia.

Which large granular lymphocytic leukemia lineage is favored?

Slide 63 · Answer — lineage and evidentiary limits

Surface CD3 positivity supports T-cell lineage.

TCR clonality provides supportive evidence of a T-cell neoplasm.

The entire diagnostic picture must remain compatible with LGL leukemia rather than an incidental T-cell clone.

Slide 64 · Five high-yield clinicopathologic principles

Cytotoxic T- and NK-lineage disease has similar granular morphology.

STAT3 activating mutations occur in a substantial minority, not all cases.

Marrow infiltrates may be sparse even when cytopenias are important.

Neutropenia, anemia, and rheumatologic associations dominate clinical reasoning.

Lineage, clonality, and context—not granules alone—establish diagnosis.

Slide 65 · Core reference

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th ed. Elsevier; 2026. Chapter 13, p. 552.

This deck is organized around the “Large Granular Lymphocytic Leukemia” section and nearby T-/NK-neoplasm context.

The original chapter PDF was not available; The supplied Markdown extraction was reviewed for the topic passage.

Slide 66 · Classification and diagnostic context

Alaggio R, et al. The 5th edition of the WHO Classification of Haematolymphoid Tumours: Lymphoid Neoplasms. Leukemia. 2022;36:1720–1748.

Calabretto G, et al. LGL Clonal Expansion and Unexplained Cytopenia: Two Clues Don’t Make an Evidence. Cancers. 2022;14:5236.

T-large granular lymphocytic leukemia. Blood Research. 2023;58(Suppl 1):S52–S57.

The fifth edition of the WHO classification of mature T-cell, NK-cell and stroma-derived neoplasms. J Clin Pathol. 2025;78:217 ff.