Chromosomal Translocations and Other Acquired Mutations

Slide 1 · Chromosomal Translocations and Other Acquired Mutations

Genetic mechanisms of white cell neoplasia

Maturation arrest

Growth and self-renewal

Apoptosis resistance

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning outcomes

1

Distinguish oncogenic gene fusions from enhancer-mediated overexpression

2

Explain differentiation arrest, proliferative signaling and survival advantages

3

Trace AID- and V(D)J-associated rearrangements to B- and T-cell development

4

Connect recurrent lesions with selected leukemias and lymphomas

Slide 3 · Acquired lesions are central to white cell neoplasia

Nonrandom genetic lesions alter programs that normally regulate leukocyte development, growth and survival.

The affected genes often serve essential functions in the corresponding normal cell

Different lesions can converge on the same malignant phenotype

Some abnormalities are sufficiently characteristic to contribute to diagnosis

Slide 4 · Recurrent chromosomal changes are not random

Chromosomal abnormalities are demonstrable in most white cell neoplasms

Translocations are especially common structural abnormalities

Recurrent breakpoints implicate particular genes in pathogenesis

Characteristic lesions connect molecular mechanism with tumor identity

Recurrence is biologic evidence—not merely a cytogenetic description.

Slide 5 · Somatic mutations differ from inherited predisposition

Acquired / somatic

Develop within a hematopoietic cell lineage

Can be selected during clonal expansion

Directly shape the neoplastic clone

Inherited predisposition

Constitutional alteration or syndrome

Raises risk of later neoplasia

Additional acquired drivers are generally needed

This lecture focuses on the acquired alterations within tumor cells.

Slide 6 · Cancer genes can be altered in several ways

Chromosomal rearrangement

Translocation or inversion alters gene context

Sequence-level mutation

Substitution or small variant changes protein or regulation

Copy-number / structural loss

Deletion or gain changes dosage or removes control

Different DNA lesion types may converge on increased growth, impaired differentiation or survival.

Slide 7 · Recurrent genetic lesions can be diagnostic

A molecular abnormality is sometimes tightly linked to one neoplasm

Specific mutations may be required in an integrated disease definition

Other lesions are shared across multiple neoplasms

Molecular results must be interpreted with morphology and lineage

Association, pathogenesis and diagnostic specificity are different questions.

Slide 8 · A translocation requires breakage and rejoining

Two DNA breaks

DNA is interrupted at two chromosomal locations

Misrejoining

DNA ends from different chromosomes are joined

Derivative chromosomes

New combinations of DNA segments are inherited by daughter cells

Misrepair can change gene regulation or create an oncogenic fusion gene.

Slide 9 · A structural change can have two molecular outcomes

Regulatory juxtaposition

Coding sequence may remain intact

Strong enhancer/promoter drives excess expression

Example: MYC near IGH regulatory elements

Fusion oncoprotein

Coding segments from two genes are joined

A chimeric protein gains abnormal activity

Example: BCR::ABL1 kinase

The location of the breakpoint determines the biochemical mechanism.

Slide 10 · Enhancer juxtaposition overexpresses an intact gene

Proto-oncogene

Gene normally regulated in its own genomic context

Active antigen-receptor enhancer

Strong neighboring regulatory element

Abnormally high expression of the original protein

Regulatory sequences are repositioned next to an oncogene

No fusion coding sequence is necessary

Slide 11 · Fusion genes generate new molecular activities

Gene A

Gene B

A::B chimeric protein

Joining coding segments can change protein structure or localization

Examples include constitutively active kinases and differentiation-blocking nuclear factors

Slide 12 · Structural breakpoints explain molecular diversity

Which gene?

Determines the normal cellular program affected

Where is the break?

Determines regulatory relocation versus a fusion coding sequence

In which cell?

Determines lineage-specific context and selective advantage

The same generic event—chromosome breakage—can produce distinct oncogenic outcomes.

Slide 13 · The major acquired-mutation effects form a triad

More growth

Kinase lesions; MYC activation

More self-renewal

Transcription-factor and chromatin abnormalities

Less apoptosis

BCL2 overexpression

Maturation arrest often accompanies increased self-renewal, particularly in acute leukemia.

Slide 14 · Differentiation arrest preserves immature progenitors

Lineage transcription program disrupted

Normal maturation becomes inefficient or blocked

Immature proliferative cells accumulate

This mechanism is especially prominent in acute leukemias.

Slide 15 · Transcription factors control lineage commitment

Hematopoietic maturation depends on ordered transcriptional programs

Transcription-factor lesions can interrupt the next differentiation step

Dominant-negative oncoproteins may suppress normal gene-regulatory functions

Accumulation of blasts reflects impaired maturation plus clonal expansion

Loss of differentiation is mechanistically distinct from a simple increase in cell division.

Slide 16 · Self-renewal gives progenitors a stem-like program

Acquired lesion in transcriptional regulator

Abnormal maintenance of self-renewal

Long-lived pool of malignant precursors

Additional growth signals can act on this persisting population.

Slide 17 · Tyrosine-kinase activation creates growth autonomy

Activating kinase mutation or fusion

Persistent intracellular phosphorylation

Increased growth and survival signaling

A normal ligand-dependent signal becomes sustained or deregulated.

Slide 18 · RAS pathways transmit oncogenic kinase signals

Constitutively active tyrosine kinase

RAS signaling

PI3K → AKT

Survival, metabolism and growth

MAPK cascade

Cell-cycle progression and growth

PI3K/AKT and MAPK as two downstream arms of RAS signaling.

Slide 19 · Apoptosis resistance extends clone survival

Pro-survival mutation

Reduced programmed cell death

Accumulation of cells that would otherwise be eliminated

BCL2 translocation exemplifies this acquired survival advantage.

Slide 20 · Distinct mutation classes cooperate

Identity / renewal lesion

Impaired maturation or enhanced self-renewal

Proliferation lesion

Expanded output from the abnormal precursor pool

Survival lesion

Less removal of abnormal progeny

Cooperating lesions explain why a single alteration is not always sufficient.

Slide 21 · Gain of function and dominant-negative effects differ

Gain of function

Creates excessive normal activity

May activate a growth pathway

May overexpress intact proto-oncogene

Dominant-negative effect

Interferes with the normal protein complex

Functionally suppresses differentiation machinery

Produces loss of a normal regulatory program

Both may result from acquired genetic alterations.

Slide 22 · Maturation state shapes the malignant phenotype

Early progenitor

Differentiation arrest often prominent

Blasts may fill marrow

Loss of effective mature blood-cell production

More mature lineage

Survival or signaling advantage may predominate

Cells may retain lineage differentiation

Distinct leukemia or lymphoma patterns arise

The phenotype depends on both the driver and the developmental stage at which it acts.

Slide 23 · Driver lesions can be classified by functional output

Primary effect

Robbins examples

Core consequence

Proliferation

MYC translocation; kinase activation

More cell division / metabolism

Self-renewal or maturation

KMT2A rearrangement; PML::RARA

Persistence of immature cells

Survival

BCL2 translocation

Resistance to apoptosis

Slide 24 · Antigen-receptor diversification creates a vulnerability

Developmental benefit

Antigen receptor genes are diversified

Necessary DNA breaks

Recombination deliberately modifies DNA

Rare error

Misrepair activates a proto-oncogene

Physiologic genomic remodeling can inadvertently create oncogenic rearrangements.

Slide 25 · V(D)J recombination belongs to precursor lymphocytes

Precursor B cells rearrange immunoglobulin loci

Precursor T cells rearrange T-cell receptor loci

Site-specific DNA cleavage enables antigen-receptor diversity

Erroneous joining may place a proto-oncogene near a receptor regulatory element

Developmental context determines the locus at risk.

Slide 26 · V(D)J misrecombination can activate an oncogene

Proto-oncogene near a DNA break

Gene normally regulated in its own genomic context

Ig/TCR locus undergoing recombination

Strong neighboring regulatory element

Oncogene repositioned beside active regulatory DNA

A DNA-diversification error becomes a heritable clonal lesion

Can occur during B- or T-cell precursor development

Slide 27 · Lymphoid lineage constrains the receptor partner

B-lineage precursor

Immunoglobulin loci are being assembled

Ig regulatory DNA may activate a proto-oncogene

Translocation partner fits B-cell lineage

T-lineage precursor

T-cell receptor loci are being assembled

TCR regulatory DNA may activate a proto-oncogene

Translocation partner fits T-cell lineage

Receptor-locus involvement is a clue to the cell of origin.

Slide 28 · Germinal-center B cells remodel their Ig genes

Antigen-stimulated B cell enters germinal center

AID expression increases

Antibody genes undergo class switching and hypermutation

This normal maturation program creates a second window for DNA damage.

Slide 29 · Activation-induced cytidine deaminase has two jobs

Somatic hypermutation

Introduces point mutations in Ig variable-region genes

Supports affinity maturation

Can inadvertently affect other genes

Class-switch recombination

Changes the Ig heavy-chain constant-region segment

Alters antibody isotype

Requires programmed recombination

AID-associated DNA lesions are productive physiologically but hazardous if mistargeted.

Slide 30 · Somatic hypermutation changes antibody affinity

AID-mediated sequence change

Point mutations in Ig genes

Clonal selection

B cells with useful receptor changes can persist

Altered affinity

Improved antigen binding may result

Mutation of a normal Ig locus is not synonymous with malignant transformation.

Slide 31 · Class switching changes isotype—not specificity

IgM heavy-chain constant region

Initial antibody class

AID-supported recombination

Constant-region DNA is replaced

Alternate heavy-chain class

Antibody effector function changes

The variable-region antigen specificity can be retained during isotype switching.

Slide 32 · AID mistargeting damages proto-oncogenes

AID acts outside the intended Ig region

Aberrant DNA lesions or point mutations occur

Oncogene dysregulation can follow

MYC rearrangements and BCL6 regulatory mutations.

Slide 33 · MYC::IGH can arise in normal germinal centers

Formation of a translocation does not, by itself, establish that a cell is malignant.

AID can induce MYC::IGH translocations in a small fraction of normal germinal-center B cells

The lesion provides a potential driver but clonal evolution still matters

Diagnostic interpretation depends on the entire cellular and tissue context

Slide 34 · MYC activation uses a powerful Ig enhancer

Chromosome 8

MYC

Chromosome 14

IGH

T(8;14): MYC driven by immunoglobulin regulatory DNA

Regulatory juxtaposition; High MYC expression, not a MYC–IGH chimeric protein

Simplified locus schematic; Not a karyogram

Slide 35 · MYC couples proliferation to biosynthesis

MYC transcriptional activity rises

Biosynthesis / Warburg-type metabolism increases

Cell growth and proliferation accelerate

This mechanism helps explain the extreme proliferative activity of Burkitt lymphoma.

Slide 36 · Burkitt lymphoma illustrates the pro-growth driver

MYC rearrangements are central to the molecular pathogenesis

IGH t(8;14) is the common partner; Ig light-chain partners also occur

MYC enhances growth-related metabolic and transcriptional programs

High proliferation coexists with abundant apoptotic cells

The molecular lesson is MYC overexpression—not blockade of apoptosis.

Slide 37 · BCL2 becomes overexpressed after t(14;18)

Chromosome 18

BCL2

Chromosome 14

IGH

T(14;18): IGH-associated BCL2 overexpression

Regulatory rearrangement that increases anti-apoptotic signaling

Simplified locus schematic; Not a karyogram

Slide 38 · BCL2 helps abnormal B cells evade apoptosis

IGH-associated BCL2 expression rises

Programmed cell death is antagonized

Germinal-center–derived neoplastic B cells persist

This is a survival advantage rather than a direct acceleration of cell-cycle entry.

Slide 39 · Follicular lymphoma exposes the survival phenotype

Normal germinal center

Many B cells undergo apoptosis

Selection eliminates unsuccessful cells

Apoptotic debris is commonly observed

Follicular lymphoma

BCL2 often overexpressed after t(14;18)

Cell death is suppressed

Apoptotic cells are characteristically sparse

The biologic signature is failure to delete cells that should die.

Slide 40 · BCL6 mutations disrupt a physiologic regulator

Mutation affects BCL6 control sequences

Normal negative autoregulation is lost

Persistent BCL6 expression impedes differentiation and growth arrest

Mistargeted somatic hypermutation is implicated in some BCL6 promoter mutations.

Slide 41 · BCL6 dysregulation has more than one route

BCL6 rearrangement

Chromosome breakpoint involves BCL6

Can alter gene regulation

Observed in a subset of DLBCL

BCL6 promoter mutation

Local acquired sequence change

May escape normal autorepression

Can likewise raise BCL6 activity

Chromosomal translocation is not the only acquired path to oncogene activation.

Slide 42 · Cyclin D1 translocation advances the cell cycle

Chromosome 11

CCND1 (cyclin D1)

Chromosome 14

IGH

T(11;14): Cyclin D1 expression increases

Up-regulates G1-to-S progression in mantle cell lymphoma

Simplified locus schematic; Not a karyogram

Slide 43 · Ig-linked lesions differ in their downstream effect

Rearrangement

Characteristic context

Main molecular output

MYC–IGH, t(8;14)

Burkitt lymphoma

Proliferation / metabolism

BCL2–IGH, t(14;18)

Follicular lymphoma

Anti-apoptotic survival

CCND1–IGH, t(11;14)

Mantle cell lymphoma

G1–S cell-cycle entry

Slide 44 · A recurrent lesion is not an entire diagnosis

The same pathway can be perturbed by different mutations across distinct hematolymphoid malignancies.

The partner gene, breakpoint and cellular lineage modify interpretation

Genotype is integrated with morphology and immunophenotype

An isolated abnormality does not reproduce a whole tumor classification

Slide 45 · BCR::ABL1 creates an oncogenic fusion kinase

Chromosome 9

ABL1

Chromosome 22

BCR

T(9;22): BCR::ABL1 fusion on derivative 22

Constitutively active tyrosine kinase; Philadelphia chromosome

Simplified locus schematic; Not a karyogram

Slide 46 · BCR::ABL1 signals without physiologic restraint

BCR supports kinase self-association

ABL kinase remains activated

RAS / JAK–STAT and related survival pathways are stimulated

Proliferation becomes less dependent on external hematopoietic growth signals.

Slide 47 · CML illustrates proliferation with maturation

BCR::ABL1 output

Growth-factor–independent expansion

Prominent granulocytic and megakaryocytic production

Differentiation remains relatively preserved

Acute leukemia pattern

Lesions can block differentiation

Immature blasts accumulate

Normal marrow output is suppressed

Kinase-driven proliferation does not necessarily imply a complete maturation block.

Slide 48 · BCR::ABL1 is both a marker and a drug target

Identification of the fusion gene is central to CML diagnosis

Chromosome analysis or molecular tests can demonstrate BCR::ABL1

Fusion-derived kinase activity provides a treatment target

Quantitative assays of the fusion transcript enable disease monitoring

Diagnostic, predictive and monitoring roles should be distinguished.

Slide 49 · PML::RARA is a nuclear fusion oncoprotein

Chromosome 15

PML

Chromosome 17

RARA

T(15;17): PML::RARA fusion protein

Abnormal transcriptional repression blocks promyelocyte maturation

Simplified locus schematic; Not a karyogram

Slide 50 · PML::RARA represses differentiation genes

Fusion receptor has altered retinoid response

Transcriptional repressors remain recruited

Myeloid progenitors fail to complete maturation

This is an archetypal transcription-factor–mediated differentiation block.

Slide 51 · Retinoids can reverse the PML::RARA program

Pharmacologic all-trans retinoic acid binds fusion protein

Repressor complexes are displaced; Degradation is promoted

Differentiation resumes and malignant promyelocytes are cleared

A mechanistic demonstration of differentiation therapy.

Slide 52 · Acute promyelocytic leukemia integrates mechanism and clinic

PML::RARA results from recurrent t(15;17)

The lesion blocks differentiation at the promyelocyte stage

The disease is associated with characteristic abnormal promyelocytes

Recognizing the molecular driver matters because differentiation therapy is effective

Molecular diagnosis can alter treatment directly.

Slide 53 · KMT2A lesions alter transcriptional self-renewal

KMT2A chromosomal rearrangement

Abnormal regulation of differentiation and renewal genes

Persistence of leukemic progenitors

KMT2A rearrangement among lesions affecting self-renewal and maturation.

Slide 54 · Fusion oncoproteins have different biochemical roles

Fusion

Biochemical category

Dominant pathogenic output

BCR::ABL1

Constitutively active kinase

Pro-growth and pro-survival signaling

PML::RARA

Abnormal nuclear regulator

Differentiation arrest

KMT2A rearrangement

Transcription/chromatin regulation

Abnormal renewal / maturation

Slide 55 · Acute leukemias often require complementary lesions

Regulatory driver

Maturation arrest / persistent self-renewal

Growth driver

Kinase or RAS pathway activation

Clonal expansion

Immature leukemic cells accumulate

Cooperation between transcription-factor and growth signaling lesions.

Slide 56 · Acquired point mutations can also drive cancer

Coding-region change

Alters activity of the encoded protein

Can increase signaling or disable a regulator

May create gain- or loss-of-function effects

Regulatory-region change

Alters how much protein is produced

Can disrupt normal negative feedback

BCL6 promoter mutations are an example

An abnormal gene sequence need not involve a visible chromosomal translocation.

Slide 57 · Epigenetic regulators are acquired-mutation targets

Mutated chromatin regulators alter DNA-accessibility and gene-expression programs

DNMT3A influences DNA methylation in AML

KMT2D and EZH2 mutations are described in follicular lymphoma

Histone regulation provides an additional route to altered cell identity

Epigenetic changes can be caused by genetic mutations.

Slide 58 · Small deletions can activate oncogenes

TAL1 proto-oncogene

Gene normally regulated in its own genomic context

Nearby active promoter after deletion

Strong neighboring regulatory element

Abnormal TAL1 transcription without reciprocal translocation

A small chromosome 1 deletion can juxtapose a promoter and TAL1

Reported by Robbins in a subset of T-cell ALL

Slide 59 · Molecular assays interrogate different features

Method

Typical molecular feature

Practical role

Conventional karyotype

Larger structural and numerical changes

Global chromosomal overview

FISH

Specific rearrangement or copy change

Targeted localization / detection

RT-PCR / PCR

Fusion transcripts or defined sequence

Targeted sensitive detection

Sequencing

Acquired sequence variants; some fusions

Molecular characterization

Slide 60 · The assay must match the suspected lesion

Clinical / morphologic question

Determine which neoplasm is suspected

Molecular target

Choose fusion, rearrangement or sequence variant

Appropriate assay

Interpret with lineage and specimen quality

A negative targeted assay only excludes lesions within its validated detection scope.

Slide 61 · Molecular findings need integrated interpretation

The genetic lesion may be diagnostic, supportive or shared by entities

Phenotype, histology, blood and marrow distribution remain relevant

AID-associated rearrangements may occur in normal germinal centers

The final diagnosis is not reducible to a single isolated sequence finding

Do not equate mutation detection with a malignant diagnosis in all circumstances.

Slide 62 · Case 1 — A kinase-driven myeloproliferation

An adult has marked granulocytic leukocytosis. Molecular testing identifies a BCR::ABL1 fusion.

What does this fusion encode, and why can mature granulocytes still predominate?

T(9;22)

Constitutive tyrosine kinase

Relatively preserved maturation

Slide 63 · Case 1 — CML mechanism resolved

BCR::ABL1 produces a constitutively active kinase.

The fusion enhances growth-factor–independent signaling

The proliferation of myeloid progenitors is increased

Unlike strong differentiation-blocking lesions, maturation can continue

The Philadelphia chromosome is a mechanism-defining molecular finding.

Slide 64 · Case 2 — An apoptosis-resistant B-cell clone

A follicular-pattern B-cell lymphoma harbors an IGH–BCL2 rearrangement.

Which malignant-cell advantage is most directly predicted?

T(14;18)

BCL2 overexpression

Reduced cell death

Slide 65 · Case 2 — Survival rather than rapid cycling

IGH-associated BCL2 expression protects cells from apoptosis.

BCL2 antagonizes programmed cell death

Abnormal B cells persist when they would normally be eliminated

This does not imply the MYC-like acceleration of biosynthesis

Tumor growth may reflect impaired removal as well as increased production.

Slide 66 · Case 3 — A promyelocyte maturation block

Acute leukemia is associated with abnormal promyelocytes and a PML::RARA fusion.

Which transcriptional defect explains the maturation arrest?

T(15;17)

Retinoid-responsive transcription factor

Repressor recruitment

Slide 67 · Case 3 — A targetable differentiation program

PML::RARA enforces transcriptional repression at physiologic retinoid levels.

Genes required for myeloid maturation are not activated

Pharmacologic all-trans retinoic acid changes fusion-protein behavior

Differentiation and elimination of abnormal cells become possible

A molecular lesion can determine a differentiation-based therapy.

Slide 68 · Case 4 — A germinal-center translocation

A highly proliferative mature B-cell tumor has t(8;14), juxtaposing MYC with IGH.

Is the principal mechanism a chimeric protein or regulatory overexpression?

MYC gene remains intact

Ig heavy-chain regulatory DNA

Increased biosynthesis / cell division

Slide 69 · Case 4 — MYC is deregulated by enhancer context

This is regulatory juxtaposition, not production of an MYC–IGH fusion kinase.

IGH regulatory elements drive inappropriate MYC expression

MYC raises cellular growth and metabolic programs

The lesion is central to Burkitt lymphoma pathogenesis

Always distinguish a locus rearrangement from a chimeric coding fusion.

Slide 70 · A comparative map of acquired lesions

Lesion

Tumor example

Molecular mechanism

MYC / IGH

Burkitt lymphoma

Proto-oncogene overexpression

BCL2 / IGH

Follicular lymphoma

Resistance to apoptosis

CCND1 / IGH

Mantle cell lymphoma

G1–S promotion

BCR::ABL1

CML

Constitutive kinase signaling

PML::RARA

Acute promyelocytic leukemia

Differentiation repression

Slide 71 · Integration: A lesion must be translated to function

DNA-level event

Rearrangement, sequence variant or deletion

Protein / regulatory consequence

Kinase, transcription factor, cell-cycle or apoptosis program

Neoplastic phenotype

Abnormal renewal, proliferation, maturation or survival

Mechanistic interpretation bridges cytogenetics, pathology and molecular diagnosis.

Slide 72 · Core references

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

Related textbook material: oncogenic translocations, structural lesions and epigenetic changes.

Disease exemplars: B-ALL, Burkitt lymphoma, follicular lymphoma, mantle cell lymphoma, AML and CML.

Schematic diagrams in this deck are newly authored as editable PowerPoint elements.