Clonal Hematopoiesis

Slide 1 · Clonal Hematopoiesis

Aging • mutant stem-cell selection • neoplastic risk • inflammation

Acquired mutation

Molecular origin

Clonal expansion

Stem-cell fitness

Clinical impact

Malignancy and inflammation

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Define clonal hematopoiesis in terms of mutation, clone and blood counts.

Explain age dependence, HSC selection and the principal epigenetic genes.

Relate mutant clone biology to malignancy and inflammatory disease.

Interpret molecular findings without mistaking a clone for overt cancer.

1

Definition

2

Mechanism

3

Clinical significance

Slide 3 · Position in hematopathology

Clonal hematopoiesis may precede overt hematologic malignancy.

It is encountered in individuals without abnormal blood counts.

Its discussion precedes acute and chronic myeloid neoplasms because of the precursor relationship.

Normal hematopoiesis

Clonal hematopoiesis

Overt neoplasm

Slide 4 · Normal hematopoiesis is hierarchical

Hematopoietic stem cells generate committed progenitors.

Progenitors mature into circulating myeloid and lymphoid cells.

A genetic change in an upstream HSC can be represented across differentiated lineages.

Hematopoietic stem cell

Myeloid cells

T lymphocytes

B lymphocytes

Schematic: Lineage output from an upstream HSC

Slide 5 · Homeostatic control versus clonal selection

Normal hematopoiesis responds to growth factors and feedback controls.

A mutant stem-cell population may expand because of increased fitness.

The mere presence of a clone does not establish malignant marrow failure.

Feedback-regulated blood cell production

Selective expansion of one mutated lineage

VERSUS

Slide 6 · Core definition

An acquired pathogenic mutation occurs in a hematopoietic clone.

The affected gene is implicated in cancer biology.

Peripheral blood counts remain normal definition.

Acquired mutation

Clonally expanded hematopoiesis

Normal blood counts

Slide 7 · Three defining requirements

Somatic genetic lesion: Not simply an inherited germline variant.

Clonality: Mutant cells are present as an expanded population.

No hematologic count abnormality at diagnosis in this definition.

1

Acquired lesion

2

Clonal expansion

3

Normal counts

Slide 8 · Clonal hematopoiesis is not leukemia

A cancer-associated mutation can exist before malignancy.

Leukemia requires disease-specific neoplastic features, not mutation detection alone.

Normal counts and lack of hematologic symptoms distinguish the textbook-described state.

Mutation-positive clone

Clinically apparent hematologic neoplasm

VERSUS

Slide 9 · What constitutes a hematopoietic clone?

A group of blood-producing cells descends from a mutated ancestral cell.

Its cells share an acquired molecular alteration.

Expansion means this lineage contributes a detectable share of hematopoiesis.

Mutated ancestral HSC

Descendant cells carrying mutation

Detectable clone

Slide 10 · Acquired and inherited variants differ

An acquired mutation develops during the individual’s lifetime.

A germline variant is present from conception across many tissues.

Interpretation of blood sequencing must preserve this distinction.

Somatic mutation in blood-cell lineage

Constitutional inherited variant

VERSUS

Slide 11 · A cancer gene mutation is not sufficient

Somatic mutations arise continually as cells age.

Most do not give rise to clinically significant clones.

Selection requires a favorable effect on stem-cell growth or survival.

Somatic mutation

Usually neutral

Occasionally growth/survival benefit

Slide 12 · The normal blood count requirement

Normal blood counts are part of the textbook’s working definition.

An affected person need not have clinical hematologic symptoms.

Molecular alterations can precede changes detected by routine hematology.

Blood counts normal?

Pathogenic somatic clone present?

Interpret in the clinical context

Slide 13 · Sequencing defines the measurable clone

DNA sequencing examines blood- or marrow-derived cells.

Mutant sequence reads reveal the variant in a cell population.

The source specifies a mutant-read fraction threshold for the working definition.

DNA from blood / marrow cells

Short sequencing reads

≥2% mutant sequencing reads

Slide 14 · The operational 2% threshold

At least 2% of sequencing reads as the diagnostic convention.

The threshold is explicitly described as somewhat arbitrary.

A threshold convention is not a biologic switch between health and malignancy.

Below working cutoff

At or above the 2% read threshold

VERSUS

Slide 15 · Read fraction is not a cell count

A fraction of mutant DNA reads is a sequencing measurement.

It should not automatically be equated with the percentage of marrow cells in the clone.

Interpret clone size in the context of the measurement being reported.

DNA from blood / marrow cells

Short sequencing reads

Mutation detected in a subset of reads

Slide 16 · A molecular finding needs context

Detection establishes that a variant is in the specimen.

Clonal hematopoiesis interpretation additionally requires normal blood counts and suitable biological context.

The same gene may carry alterations in hematologic or nonhematologic neoplasms.

Where did the sampled DNA originate?

Are blood counts normal?

Which tissue harbors the variant?

Slide 17 · Age is the dominant epidemiologic pattern

Clonal hematopoiesis is uncommon before age 50 years.

Frequency increases progressively in later life.

Aging supplies time for mutations and selection of advantaged stem-cell clones.

1

Early life

2

Accumulated mutations

3

Selection

4

Older adulthood

Slide 18 · Prevalence rises markedly with age

Approximately 10% are affected by age 70 estimate.

The estimate approaches 30% by age 90.

These are age-specific approximations, not a patient-specific prediction.

Approximate proportion affected

Age 70

≈10%

Age 90

≈30%

Not a continuous interpolated curve

Slide 19 · Age and mutation accumulation

The source describes spontaneous base deamination throughout life.

Accumulation of genetic variants does not imply that all confer fitness.

Occasional driver mutations may produce selective expansion.

Mutations arise over time

Most are inconsequential

Rare beneficial variants expand

Slide 20 · Mutational origin: Spontaneous deamination

Cytosine or methyl-cytosine can undergo spontaneous deamination.

This is described as an ongoing process in multiple cell types.

Hematopoietic stem cells acquire such lesions during life.

Cytosine / methyl-cytosine

Spontaneous deamination

Occasional acquired sequence change

Slide 21 · Mutation is followed by selection

Mutation generation and clonal expansion are separate processes.

A change that improves stem-cell fitness can increase the size of its descendant population.

The resulting clone may be detected without blood-count abnormalities.

1

Acquired mutation

2

Fitness advantage

3

Clonal expansion

4

Sequencing detection

Slide 22 · Growth and survival advantages

A mutated stem cell may proliferate more effectively than competitors.

Alternatively, greater survival may allow progressive representation.

Both lead to disproportionate contribution to hematopoiesis.

Selective fitness advantage

Growth advantage

Survival advantage

Slide 23 · Most somatic mutations do not expand

Cells accumulate changes without necessarily altering tissue behavior.

Only some changes modify oncogene or tumor-suppressor function.

A detectable clone therefore reflects mutation plus selection and persistence.

Many acquired variants

Few alter cellular fitness

Selected clone persists

Slide 24 · The stem-cell compartment matters

An affected HSC can persist and continuously supply differentiated progeny.

An early mutation can be shared across different blood-cell lineages.

This explains why blood-cell mutation signals may antedate distinct neoplasms.

Hematopoietic stem cell

Monocytes

T lineage

B lineage

Schematic: Lineage output from an upstream HSC

Slide 25 · Clonal expansion is not synonymous with blasts

Expansion of mature blood-cell progeny may coexist with normal counts.

Myeloid leukemia instead features abnormal immature myeloid-cell accumulation.

The essential comparison is a precursor clone versus a manifested neoplasm.

Expanded molecular clone

Abnormal blast accumulation

VERSUS

Slide 26 · TET2 and DNMT3A predominate

TET2 and DNMT3A are the most commonly mutated genes named in the source.

Both participate in regulation of DNA methylation.

Their disruption alters epigenetic control relevant to cell state and differentiation.

TET2

DNA methylation regulation

DNMT3A

DNA methylation regulation

Altered epigenetic regulation

Slide 27 · TET2: A recurrent epigenetic driver

TET2 is identified as a tumor-suppressor gene.

It regulates the DNA methylation landscape.

TET2-mutated clones are particularly associated with inflammatory consequences.

TET2 mutation

Altered epigenetic control

Clonal and inflammatory effects

Slide 28 · DNMT3A: Another major driver

DNMT3A is a tumor-suppressor gene emphasized by Robbins.

It regulates DNA methylation-dependent gene expression.

Altered stem-cell regulation can favor clonal persistence or expansion.

DNMT3A mutation

DNA methylation dysregulation

HSC clonal selection

Slide 29 · Why DNA methylation matters

DNA methylation is a chemical modification with effects on gene expression.

Gene-expression programs influence hematopoietic maturation.

Mutations in epigenetic regulators can change cell behavior without altering blood counts initially.

DNA methylation programs

Regulated gene expression

Differentiation and cell fitness

Slide 30 · A gene is not a diagnosis

The same recurrent gene may be mutated in clonal hematopoiesis and malignancy.

A mutation must be interpreted with the blood count and overall disease phenotype.

TET2 or DNMT3A positivity alone does not prove leukemia.

TET2 / DNMT3A variant

Diagnostic integration is required

VERSUS

Slide 31 · Clonal hematopoiesis creates cancer risk

Most affected individuals do not immediately develop a neoplasm.

The textbook gives an approximate overall hematologic-neoplasm risk of 1% per year.

Risk varies substantially by clone size and mutation identity.

Baseline estimate

≈1% / year

Higher concern

Large clones

Higher concern

Splicing-factor variants

Slide 32 · The overall risk estimate is an average

Approximately 1% per year is a population-level textbook estimate.

Individual risk may be considerably above or below that figure.

It must not be applied uniformly to every molecular finding.

Average population estimate

Heterogeneous individual risk

VERSUS

Slide 33 · Clone size influences progression risk

Larger clones are associated with a greater neoplastic risk.

Clones involving 20% or more of marrow cells.

This cell-based description is different from the 2% mutant-read cutoff.

Larger clonal contribution

Greater high-risk representation

Higher progression concern

Slide 34 · Mutation identity also influences risk

Cancer-gene mutations do not have identical clinical implications.

Mutations encoding RNA splicing factors are particularly associated with increased risk.

Risk interpretation should combine variant identity with clone size.

Higher neoplastic concern

Large clone

Splicing-factor mutation

Slide 35 · Risk factors should be integrated

A low-level mutation and a large clone need not carry the same prognosis.

Variant identity adds risk information that clone burden alone cannot supply.

The textbook advocates improved prediction models for complication risk.

1

Clone size

2

Variant identity

3

Clinical context

Slide 36 · Myeloid neoplasms are the principal outcome

Myeloid neoplasms occur most frequently among subsequent hematologic cancers.

Their cell of origin is within the hematopoietic progenitor hierarchy.

The antecedent clone can carry mutations retained in the malignancy.

Hematopoietic clone

Selected progenitor

Myeloid neoplasm

Slide 37 · Lymphoid neoplasms also show association

Risks of T-cell tumors and B-cell tumors are also increased.

This is consistent with mutation occurring in an upstream multipotent stem cell.

A precursor lesion can therefore predate tumors of different lineages.

Hematopoietic stem cell

Myeloid descendants

T-cell descendants

B-cell descendants

Schematic: Lineage output from an upstream HSC

Slide 38 · Shared variants support a precursor relationship

Subsequent neoplasms commonly contain mutations present in the prior clone.

This continuity supports a precursor–product relationship.

A shared molecular lesion is more informative than simple chronological coincidence.

Earlier clone

Later hematologic neoplasm

Same acquired mutation(s)

Slide 39 · Clonal evolution is not inevitable

An advantaged clone may remain clinically silent.

A precursor–product relationship does not imply that every clone progresses.

The textbook supports increased risk, not certainty of transformation.

Stable clone

Possible evolution

Clinical neoplasm

Slide 40 · Two major consequence pathways

One branch concerns transformation into hematologic neoplasia.

A second branch concerns inflammation and chronic organ disease.

Both may arise despite initially normal blood counts.

Clonal hematopoiesis

Neoplastic progression

Inflammatory injury

Slide 41 · Inflammation is a major noncancer effect

Clonal hematopoiesis is associated with a systemic proinflammatory state.

Mutant hematopoietic cells can alter inflammatory responses.

This may increase the severity of prevalent chronic disorders.

Mutant blood-cell descendants

Amplified inflammation

Chronic tissue damage

Slide 42 · TET2 links clones to innate immunity

The TET2 association is especially strong for inflammatory disease.

The source implicates epigenetic reprogramming of monocytes and macrophages.

This modifies how these cells respond to inflammatory stimulation.

TET2-mutant hematopoiesis

Monocytes / macrophages

Altered inflammatory responsiveness

Slide 43 · Monocytes and macrophages as effectors

They arise from hematopoietic lineages and participate in tissue inflammation.

Epigenetic changes can alter the intensity of their responses.

The consequence extends outside the bone marrow to organ injury.

Mutant hematopoietic stem cell

Circulating monocyte

Tissue macrophage

Inflammatory response

Slide 44 · Hypersensitivity to inflammatory stimuli

TET2-associated programming renders monocytes and macrophages unusually responsive.

Greater inflammatory reactivity provides a plausible disease-amplification mechanism.

This as an apparent mechanism rather than a complete causal account.

Proinflammatory stimulus

Heightened mutant-cell response

More tissue inflammation

Slide 45 · The inflammasome–IL-1 pathway

IL-1 signaling and inflammasome activity are involved in experimental inflammation.

In animal models, their inhibition protects against tissue damage.

Animal-model protection is not equivalent to proven routine human preventive therapy.

Inflammasome activity

IL-1-associated inflammation

Tissue injury

Slide 46 · Atherosclerosis association

Clonal hematopoiesis is linked to greater severity of atherosclerotic disease.

The proposed connection involves inflammation from mutant myeloid-cell descendants.

Cardiovascular consequences are clinically important beyond cancer risk.

Clonal hematopoiesis

Proinflammatory cells

Atherosclerotic injury

Slide 47 · Chronic liver disease association

Nonalcoholic liver disease among affected chronic disorders.

Amplified inflammatory responses offer a proposed shared mechanism.

This association does not establish the clone as the sole cause of liver disease.

Mutant hematopoietic cells

Increased inflammatory tone

Liver disease severity

Slide 48 · Chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease is also among the associated conditions.

Altered host inflammatory reactivity may amplify tissue injury.

The association broadens the clinical relevance beyond marrow pathology.

CH-associated inflammation

Lung tissue inflammatory response

Greater COPD severity

Slide 49 · Consequences are not restricted to cancer

Noncancer mortality is increased in individuals with clonal hematopoiesis.

Cardiovascular disease is a prominent contributor.

This changes the clinical interpretation of a superficially silent molecular state.

Clonal hematopoiesis

Neoplasia risk

Cardiovascular risk

Other inflammation

Slide 50 · Symptoms may be absent at diagnosis

Individuals usually lack symptoms attributable to hematologic abnormalities.

Normal blood counts are expected in the definition employed here.

Biological risk may nonetheless be clinically relevant.

Silent hematologic presentation

Potential long-term complications

VERSUS

Slide 51 · Red cell distribution width association

A higher RDW is associated with clonal hematopoiesis.

The basis for the association remains uncertain.

RDW is also independently associated with mortality.

Elevated RDW

Observed association

Mechanistic basis unresolved

Slide 52 · RDW should not be used alone

RDW is an indirect hematology measure, not a clone-specific molecular assay.

An increased RDW is not sufficient to diagnose clonal hematopoiesis.

Its mechanistic association with the clone is unresolved.

Nonspecific RDW association

Mutation-based clonal identification

VERSUS

Slide 53 · Incidental detection in tumor sequencing

Sequencing of solid malignancies can incidentally detect blood-cell mutations.

Infiltrating leukocytes can contribute DNA to the specimen.

TET2 or DNMT3A calls may therefore derive from blood cells rather than carcinoma cells.

Solid-tumor specimen

Admixed blood-cell DNA

Detected hematopoietic variant

Slide 54 · Distinguish tumor from hematopoietic DNA

A mutation reported in tumor sequencing is not automatically tumor-intrinsic.

The cellular source must be considered when clonal-hematopoiesis genes are found.

Molecular interpretation should be integrated with the sampled tissue and hematology data.

Was the assay performed on mixed-cell tissue?

Could the variant be hematopoietic?

Correlate with blood and tumor context

Slide 55 · Teaching case: Incidental blood finding

Scenario: An older adult with normal blood counts undergoes blood sequencing.

A pathogenic acquired TET2 variant is detected above the textbook threshold.

Question: Does this finding alone establish leukemia?

Teaching scenario

Older adult; Normal blood counts

Somatic TET2-positive clone

No signs of hematologic disease

Slide 56 · Case interpretation: A precursor, not cancer

The described pattern is compatible with clonal hematopoiesis.

The clone confers risk but does not prove an overt neoplasm.

Counseling must distinguish an estimated population risk from an individual prediction.

Detected clone

No hematologic phenotype

Risk-informed interpretation

Slide 57 · Teaching case: A lung tumor sequence

Scenario: DNA from a lung carcinoma sample contains a DNMT3A mutation.

The sample may include nonmalignant blood cells.

Question: Can the sequencing call automatically be assigned to the carcinoma?

Teaching scenario

Lung carcinoma specimen

DNMT3A variant reported

Leukocytes may contribute DNA

Slide 58 · Case interpretation: Determine cell origin

Hematopoietic contamination is a recognized explanation.

A detected cancer-associated gene is not necessarily altered in the solid-tumor cells.

Avoid attributing biology or therapy implications to the tumor without support.

Variant detected in bulk tissue

Consider admixed blood cells

Do not assume tumor origin

Slide 59 · Teaching case: Contrasting clone risks

Scenario A: A small clone with a common epigenetic-driver variant.

Scenario B: A much larger clone with a splicing-factor variant.

Question: Should both be assigned identical neoplastic risk?

Teaching scenario

Different clone burdens

Different mutation classes

Normal counts at diagnosis

Slide 60 · Case interpretation: Risk is heterogeneous

Large clones and splicing-factor mutations as higher-risk features.

The overall ≈1% annual estimate cannot capture all risk strata.

Prediction is a research focus; Avoid claiming precise individualized probabilities.

Baseline estimate

≈1% / year

Higher concern

Large clones

Higher concern

Splicing-factor variants

Slide 61 · Prevention remains an evolving field

Risk-stratification models are under development.

Anti-inflammatory interventions are being investigated as potential prevention strategies.

Animal-model evidence cannot be presented as a proven standard-of-care indication.

Identify higher-risk subgroups

Study prevention strategies

Require clinical validation

Slide 62 · Integrated mechanism map

Somatic mutation and stem-cell selection create a stable clone.

Clone-associated outcomes include hematologic evolution and inflammation.

Interpretation combines clinical hematology and the molecular specimen context.

Mutant HSC clone

Neoplastic evolution

Inflammatory effects

Slide 63 · Five clinicopathologic take-home points

Clonal hematopoiesis can be present with normal counts.

Age, TET2 / DNMT3A and stem-cell selection explain much of the biology.

Hematologic progression risk varies with clone burden and gene identity.

Cardiovascular and chronic inflammatory disease associations are clinically relevant.

Incidental molecular findings demand cell-of-origin interpretation.

1

Identify

2

Risk stratify

3

Interpret

Slide 64 · Foundational reading

Robbins, Cotran & Kumar: Pathologic Basis of Disease, 11th edition (2026).

Chapter 13 discussion of myeloid neoplasms and clonal hematopoiesis.

This lecture follows the supplied textbook excerpt; no external classification updates are substituted.

Textbook chapter

Clonal hematopoiesis section

Parent myeloid-neoplasm context