Pathogenesis of Familial Breast Cancer

Slide 1 · Pathogenesis of Familial Breast Cancer

Inheritance • tumor-suppressor loss • DNA repair • therapeutic vulnerability

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Distinguish inherited susceptibility from an established breast carcinoma.

Explain autosomal-dominant predisposition and biallelic tumor-suppressor inactivation.

Connect BRCA-associated homologous recombination failure to genomic instability.

Interpret major hereditary genes, tumor phenotypes, and synthetic lethality.

Slide 3 · Familial cancer begins with susceptibility, not a tumor

Inherited pathogenic susceptibility variant

Acquired changes in breast epithelial cells

Loss of growth control / genome stability

Malignant clonal evolution

A germline variant increases risk; Additional somatic events are required for cancer.

Slide 4 · Hereditary contribution is broader than single-gene syndromes

25–35%

Breast cancers estimated to involve inherited susceptibility variants

8–17%

Breast cancers associated with moderate- or high-penetrance single-gene mutations

15–20%

Additional familial susceptibility described beyond monogenic forms

The source describes partially overlapping conceptual risk categories; Do not add them as independent totals.

Slide 5 · Penetrance expresses the probability of disease

Genotype

A person inherits a susceptibility variant.

The inherited allele is present in normal cells.

Inheritance alone does not prove cancer will develop.

Phenotype

Penetrance: Risk of developing disease in a carrier.

Age and specific mutation influence observed risk.

The same gene can have different penetrance across variants.

Penetrance is a probabilistic property, not a binary prediction.

Slide 6 · High penetrance versus moderate and low penetrance

High / moderate penetrance

Larger risk attributable to an individual allele.

May form a recognizable familial cancer syndrome.

Tumor suppressor defects often affect repair or growth control.

Low penetrance / polygenic susceptibility

Single variants usually confer smaller increments of risk.

Combinations of polymorphisms may interact.

May explain familial clustering without a classic monogenic syndrome.

Risk magnitude and familial aggregation are not synonymous.

Slide 7 · Family history acts as a clinical clue

Breast cancer in a first-degree relative (mother, sister, or daughter).

Multiple affected relatives across a family.

Cancer diagnosed at an unusually early age.

These patterns raise suspicion but do not establish a pathogenic variant.

Slide 8 · Family history and molecular inheritance are different observations

Observed family clustering

Hypothesis: Inherited risk variant(s)

Appropriate genetic evaluation

Variant-based interpretation

Clinical pedigree information suggests inherited susceptibility; Molecular testing addresses genotype.

Slide 9 · Hereditary predisposition follows autosomal-dominant segregation

At the family level

A pathogenic allele can be inherited from one affected or unaffected carrier parent.

Risk can occur across generations.

Inheritance of one mutant allele is sufficient to create susceptibility.

At the neoplastic-cell level

The intact allele continues to provide tumor-suppressor function.

Tumor evolution commonly involves acquired loss of that remaining allele.

Biallelic loss produces the cellular defect.

Dominant inherited predisposition and recessive cellular tumor-suppressor loss are compatible.

Slide 10 · Inheritance is not equivalent to inevitable disease

Not every carrier has the same age-specific cancer risk.

The exact BRCA1/BRCA2 variant influences penetrance and age of onset.

Other genetic factors may modify individual risk.

Disease phenotype emerges through subsequent tumor evolution.

Slide 11 · Recognize two classes of inherited risk

Characteristic

Monogenic higher-risk

Polygenic / lower-risk

Molecular basis

One pathogenic susceptibility allele

Multiple low-effect variants

Family pattern

Sometimes a strong recognizable pedigree

May be more subtle or complex

Risk estimate

Depends on gene and variant

Depends on combined variant effects

Cancer emergence

Somatic evolution still required

Somatic evolution still required

Conceptual comparison; No polygenic numerical risk score is assumed.

Slide 12 · The inherited lesion usually affects a tumor suppressor

Important high-penetrance genes participate in genomic stability or cell-growth control.

Risk-conferring inherited alleles typically contain loss-of-function mutations.

Inactivation of a second allele can eliminate the remaining protective function.

Genomic instability helps epithelial cells accumulate transforming alterations.

Slide 13 · A tumor suppressor requires two functional hits for loss

Normal alleles: + / +

Germline variant: − / +

Somatic second hit: − / −

Deficient suppressor function

Schematic allele states: + = functioning allele; − = loss-of-function allele.

Slide 14 · Inherited first hit: Every cell carries the susceptible state

Carrier normal tissue

One inherited defective susceptibility-gene copy.

A functional allele remains.

Normal tissues may still maintain DNA repair.

Emerging neoplastic clone

A vulnerable cell acquires additional lesions.

Loss of the remaining allele may confer a strong selective advantage.

The deficient lineage can expand.

This is a two-hit mechanism for tumor suppressors; It does not imply all tissues form tumors.

Slide 15 · The second hit can arise by multiple mechanisms

Inherited loss-of-function allele

Remaining allele: Mutation, deletion, or silencing

Biallelic gene inactivation

Failure of protective pathway

Methylation-dependent silencing is one described route to loss of remaining-allele function.

Slide 16 · Mutation, deletion, and epigenetic silencing are distinct

Second-hit mechanism

Molecular consequence

Pathogenic interpretation

Somatic mutation

Sequence alteration of intact allele

Protein function may be lost

Deletion

Physical loss of the remaining allele

No intact gene copy retained

Methylation-dependent silencing

Suppressed expression without required sequence deletion

Functionally inactivated allele

All are listed by Robbins as possible mechanisms for the remaining tumor-suppressor allele.

Slide 17 · A two-hit model explains cancer development in carriers

Starting condition

One pathogenic allele is inherited.

Normal cellular growth control can persist.

Risk is elevated before a tumor exists.

A breast epithelial cell acquires a second hit

Protective gene function is lost

Genomic damage or proliferative escape increases

Schematic causal chain; Additional oncogenic events are required for malignancy.

Slide 18 · Inherited predisposition and somatic driver accumulation cooperate

Susceptibility allele

Second-hit inactivation

DNA damage / pathway dysregulation

Additional drivers and clonal selection

Breast carcinoma

The initiating inherited genotype influences subsequent cancer phenotype, but does not determine it absolutely.

Slide 19 · BRCA1 and BRCA2 dominate monogenic familial disease

80–90%

Single-gene familial breast cancers attributed to BRCA1 or BRCA2 mutations

3–6%

All breast cancers attributed to BRCA1/BRCA2 germline mutations

These figures have different denominators; They are not directly comparable percentages.

Slide 20 · BRCA1 and BRCA2 occupy different chromosomal loci

BRCA1

Chromosome 17q21.

Large susceptibility gene with many pathogenic sequence variants.

Encoded product is important for genomic maintenance.

BRCA2

Chromosome 13q12.3.

Large susceptibility gene with many pathogenic sequence variants.

Encoded product is important for genomic maintenance.

The presence of many variants makes interpretation of a genetic test more demanding.

Slide 21 · BRCA1 and BRCA2 variants are heterogeneous

Hundreds of disease-associated variants are distributed across the coding regions.

Different pathogenic variants can confer different risks and ages of onset.

Inconsequential polymorphisms are also common.

Identifying a sequence change is not the same as establishing clinical pathogenicity.

Slide 22 · The BRCA genes protect against loss of genomic integrity

DNA double-strand break

BRCA-associated DNA-repair response

Homologous recombination with a sister chromatid

Restored genomic continuity

Schematic normal pathway, deliberately omitting unverified mechanistic substeps.

Slide 23 · BRCA deficiency changes the consequence of DNA damage

Functional BRCA repair pathway

Homologous recombination is available.

An intact sister-chromatid template can guide accurate repair.

Damage is less likely to persist as a driver of instability.

BRCA-deficient tumor cell

Double-strand repair is compromised.

Genomic abnormalities can accumulate.

Clonal selection may favor cells acquiring further oncogenic changes.

Mechanism is the key link between inherited genotype and malignant evolution.

Slide 24 · BRCA1- and BRCA2-associated tumors need not look alike

BRCA1-associated phenotype

Most cancers in carriers are triple-negative.

Triple-negative: ER-negative, PR-negative and HER2-negative.

Reflects an association, not an exclusive diagnosis.

BRCA2-associated phenotype

Most breast cancers in carriers are ER-positive.

Hormone-receptor expression does not rule out hereditary BRCA2 disease.

Variant-specific effects remain relevant.

Tumor phenotype suggests biological pathways but cannot establish germline status alone.

Slide 25 · Tumor subtype and germline genotype are different tests

Clinical question

Relevant evidence

What it cannot prove alone

What phenotype has developed?

Tumor ER / PR / HER2 assessment

Presence of a germline pathogenic variant

What risk allele is inherited?

Germline molecular analysis

Actual phenotype of a tumor

What pathway is defective in tumor?

Integrated molecular and pathology interpretation

Every repair-deficient tumor has a BRCA mutation

ER, estrogen receptor; PR, progesterone receptor; HER2, ERBB2 protein.

Slide 26 · BRCA-associated susceptibility extends beyond the breast

Ovarian and related epithelial malignancies are important associated cancers.

Pancreatic and prostatic cancer risks are also increased.

Male BRCA2 carriers have increased susceptibility to breast cancer.

The tumor spectrum differs between genes and inherited variants.

Slide 27 · The sex of a carrier changes expression of risk

Female carriers

Breast cancer is a major associated malignancy.

Age-specific penetrance varies substantially.

Ovarian cancer susceptibility may coexist.

Male carriers

BRCA2 variants increase male breast-cancer risk.

Prostate and pancreatic risks may also be elevated.

Carrier status matters even without female breast cancer.

Sex-specific clinical expression does not alter autosomal inheritance.

Slide 28 · BRCA penetrance should not be presented as one fixed percentage

Risk depends on the precise pathogenic allele.

Different variants can have different onset distributions.

Other susceptibility alleles can modify familial risk.

A population average cannot be converted into certainty for an individual carrier.

Slide 29 · Genetic-test interpretation requires a meaningful variant classification

Sequence variant identified

Establish whether clinically pathogenic

Interpret with personal and family history

Discuss disease-risk implications

Numerous disease-associated variants and common inconsequential polymorphisms.

Slide 30 · Founder variants illustrate ancestry-specific genetic risk

~1 in 400

General-population frequency of BRCA variants that increase risk, as

~1 in 40

Ashkenazi Jewish population frequency of three founder variants in the source

These figures are textbook estimates, not individual predictive probabilities or a current population screening recommendation.

Slide 31 · Founder mutations do not represent all pathogenic BRCA variants

Founder-variant testing

Targets recurrent variants in a particular ancestral population.

Useful for understanding why variant prevalence can vary by ancestry.

A negative founder-variant result is not the same as absence of all hereditary risk.

Broad sequence evaluation

Large genes harbor many variants across coding regions.

Interpretation must separate disease-causing changes from polymorphisms.

Clinical context remains essential.

The three Ashkenazi-associated founder variants described: Two in BRCA1, one in BRCA2.

Slide 32 · The susceptibility-gene spectrum has several functional classes

Biological role

Important examples

Main teaching implication

DNA repair / DNA-damage response

BRCA1, BRCA2, PALB2, ATM, CHEK2, RAD51C, RAD51D

Failure of genomic maintenance

Other growth / genome surveillance

TP53, PTEN, STK11, NF1

Altered checkpoint or growth-control pathways

Cell-cell adhesion

CDH1

Distinctive lobular breast-cancer association

Functional grouping is simplified; Several gene products have multiple interacting roles.

Slide 33 · Hereditary susceptibility genes do not confer identical risk

Higher-penetrance syndromes

BRCA1, BRCA2, PALB2.

TP53, PTEN, STK11, CDH1.

Gene-specific cancer spectrum often helps define the syndrome.

Moderate-penetrance susceptibility

ATM, CHEK2, NF1, RAD51C and RAD51D.

Usually smaller individual breast-cancer risk effect than BRCA1/BRCA2.

Cancer associations and phenotypes still differ by gene.

This grouping follows the hereditary susceptibility table in the source; Exact individualized risk is not inferred.

Slide 34 · PALB2 links hereditary breast cancer to DNA-repair failure

PALB2

Mechanistic role

Participates in the homologous recombination DNA-repair system.

Interacts functionally with BRCA-associated genome-maintenance pathways.

Associated tumor pattern / spectrum

Tumors may be ER-positive or triple-negative.

Breast and additional epithelial cancer susceptibility is described.

Clinical interpretation

Biallelic inherited abnormalities can produce a Fanconi anemia phenotype.

Genetic context determines whether a variant is disease-causing.

The OCR table spells “PALPB2”; The surrounding source prose consistently identifies PALB2.

Slide 35 · ATM coordinates response to DNA damage

ATM

Mechanistic role

DNA-damage response linked to homologous recombination and checkpoint signaling.

Loss impairs appropriate response to DNA double-strand breaks.

Associated tumor pattern / spectrum

Most associated breast cancers express estrogen receptor.

Included among moderate-penetrance predisposition genes.

Clinical interpretation

Biallelic germline abnormalities can cause ataxia-telangiectasia.

Carrier-associated cancer risk is distinct from the recessive syndrome.

Slide 36 · CHEK2 connects damage signaling with cell-cycle control

CHEK2

Mechanistic role

Checkpoint pathway involved in genome surveillance after DNA damage.

Works in an interconnected DNA-damage response network.

Associated tumor pattern / spectrum

Associated breast cancers are often ER-positive.

Additional cancer associations are reported in the source table.

Clinical interpretation

Moderate-penetrance susceptibility gene.

Tumor receptor phenotype alone is insufficient to determine genotype.

Slide 37 · RAD51C and RAD51D connect susceptibility with repair

RAD51C / RAD51D

Mechanistic role

Proteins associated with homologous recombination repair.

Maintain the response to DNA double-strand breaks.

Associated tumor pattern / spectrum

Breast tumors may be triple-negative.

Ovarian and fallopian-tube cancer susceptibility is noted.

Clinical interpretation

Grouped among moderate-penetrance breast-cancer genes.

A tumor phenotype cannot uniquely identify an inherited gene.

Slide 38 · BRCA2 and PALB2 deficiency can have biallelic germline effects

Monoallelic inherited defect

Predisposes to adult cancer after somatic evolution.

A second hit in tumor tissue can inactivate repair.

A typical hereditary tumor-predisposition model.

Biallelic germline defect

The source associates BRCA2 and PALB2 biallelic variants with Fanconi anemia.

The phenotype is not simply “twice the carrier risk.”

Illustrates how genotype dosage changes disease mechanism.

Distinguish recessive constitutional disease from dominant cancer susceptibility.

Slide 39 · TP53-associated familial breast cancer is a different pathway

TP53

Mechanistic role

Tumor suppressor governing responses to genomic damage and cellular stress.

Broad cancer predisposition differs from BRCA-centered repair deficiency.

Associated tumor pattern / spectrum

Associated with Li–Fraumeni syndrome.

Associated breast cancers often express both ER and HER2.

Clinical interpretation

Sarcomas, leukemia, and brain tumors occur in the cancer spectrum.

Family phenotype must be interpreted across organ systems.

Slide 40 · PTEN-associated predisposition combines neoplasia and growth control

PTEN

Mechanistic role

Tumor-suppressive regulation of cellular growth signaling.

Biology differs from core homologous recombination proteins.

Associated tumor pattern / spectrum

Cowden syndrome association.

Benign tumors and thyroid/endometrial malignancies are described.

Clinical interpretation

Breast carcinomas can show apocrine differentiation.

Breast cancer is one component of a multisystem syndrome.

Slide 41 · STK11-associated predisposition is syndromic

STK11

Mechanistic role

Tumor-suppressor pathway regulating cell-growth programs.

Not classified as a core BRCA homologous-recombination gene.

Associated tumor pattern / spectrum

Peutz–Jeghers syndrome.

Susceptibility also includes ovarian, pancreatic and colonic neoplasms.

Clinical interpretation

Associated with benign gastrointestinal polyps.

Extra-breast manifestations can identify syndromic susceptibility.

Slide 42 · CDH1-associated hereditary cancers have a lobular pattern

CDH1

Mechanistic role

Encodes an epithelial cell-adhesion factor.

Loss alters intercellular cohesion rather than BRCA-like repair directly.

Associated tumor pattern / spectrum

Breast carcinomas are predominantly lobular.

Syndromic association with diffuse gastric carcinoma.

Clinical interpretation

A tumor’s lobular histology may point toward this gene.

Histologic association is not sufficient to diagnose inherited CDH1 susceptibility.

Slide 43 · NF1-associated breast cancer is part of a wider syndrome

NF1

Mechanistic role

Tumor-suppressive control of growth-related signaling.

Listed among moderate-penetrance susceptibility genes.

Associated tumor pattern / spectrum

Neurofibromatosis type 1 with multiple neurofibromas and cutaneous findings.

Other associated neoplasms include neural-system tumors.

Clinical interpretation

Non-breast clinical findings may inform genetic evaluation.

A syndrome-level clinical assessment is more useful than subtype alone.

Slide 44 · Different genes predict different associated neoplasms

Germline susceptibility

Associated cancer pattern in source

Breast phenotype clue

BRCA1

Ovarian, pancreatic, prostate

Often triple-negative

BRCA2

Ovarian, pancreatic, prostate

Often ER-positive; Male breast risk

TP53

Sarcoma, leukemia, brain

Often ER-positive / HER2-positive

CDH1

Diffuse gastric carcinoma

Often lobular type

PTEN

Thyroid, endometrium

May be apocrine

Phenotype clues are tendencies, not diagnostic criteria.

Slide 45 · Why genotype and morphology are related but not interchangeable

Different inherited gene defects

Different biological pathways affected

Different selection pressures in breast epithelium

Characteristic tumor associations

Many tumors deviate from characteristic patterns; Molecular and morphologic evidence are complementary.

Slide 46 · Double-strand breaks threaten genomic continuity

DNA double-strand breaks interrupt both strands of a DNA duplex.

Incorrect or incomplete repair can destabilize the genome.

BRCA-associated pathways help preserve genomic information after injury.

The resulting repair phenotype links hereditary risk to therapeutic vulnerability.

Slide 47 · Homologous recombination uses a sister-chromatid template

Double-strand DNA break

Identify intact homologous sister template

Template-guided repair

Preserved DNA sequence

Conceptual schematic; The textbook provides the template-guided principle, not every enzymatic step.

Slide 48 · Homologous recombination differs from single-strand repair

Double-strand break repair

Repair using a normal sister chromatid is homologous recombination.

BRCA1, BRCA2 and related genes are central to this response.

Loss causes homologous recombination deficiency.

Single-strand repair mechanisms

PARP participates in repair pathways dealing with single-strand lesions.

Inhibition can increase damage burden.

Repair-pathway redundancy can determine whether a cell survives.

This distinction is the core of the textbook PARP synthetic-lethality explanation.

Slide 49 · A network of susceptibility genes supports genome maintenance

DNA damage recognized

ATM / CHEK2 damage response

BRCA1 / BRCA2 / PALB2 / RAD51-related repair

Genomic integrity maintained

Simplified functional grouping: ATM and CHEK2 act prominently in DNA-damage signaling; Not identical biochemical roles.

Slide 50 · Loss of repair capacity facilitates oncogenic evolution

Inactivation of repair gene

Impaired high-fidelity DNA repair

Persistence / misrepair of DNA lesions

Genomic instability

Selection of malignant clones

Genome instability increases opportunity for additional driver alterations; It is not itself the sole defining cause of cancer.

Slide 51 · What is homologous recombination deficiency?

Tumor cells lack effective homologous recombination repair of DNA double-strand breaks.

BRCA1 or BRCA2 biallelic loss is a canonical route to deficiency.

Other genes in the DNA-damage response network may produce related deficits.

This is a tumor functional phenotype, not just a germline family-history category.

Slide 52 · Repair-intact and repair-deficient cells face different options

Cellular condition

Double-strand repair reserve

Potential consequence

Normal repair-intact cell

Homologous recombination available

Can tolerate repair-pathway stress better

Repair-deficient tumor cell

Homologous recombination compromised

Greater dependence on residual repair routes

Repair-deficient + PARP inhibition

Multiple pathways stressed

DNA damage may become lethal

Educational mechanism; No drug-response rate or universal sensitivity is implied.

Slide 53 · PARP inhibition creates a repair-pathway dependency

Homologous recombination-deficient tumor

Inhibit PARP-associated repair pathway

Accumulating unrepaired DNA damage

Cell death

The source models PARP inhibitor susceptibility through repair-pathway loss and synthetic lethality.

Slide 54 · Synthetic lethality is a genetic interaction

Single defect: Often survivable

A cell may survive loss of one compensatory repair pathway.

Alternative pathways preserve a degree of viability.

A functioning pathway can buffer another defect.

Combined defects: Potentially lethal

Tumor: Homologous recombination deficient.

Treatment: Pharmacologic PARP-pathway inhibition.

The combined repair impairment can trigger tumor cell death.

Synthetic lethality describes the interaction of two perturbations, not the toxicity of a drug in all cells.

Slide 55 · The synthetic-lethality logic can be represented as a matrix

Homologous recombination

PARP-related function

Expected qualitative outcome

Intact

Available

DNA repair capacity preserved

Deficient

Available

Tumor may remain viable

Intact

Inhibited

Alternate repair remains available

Deficient

Inhibited

High vulnerability to lethal DNA damage

Schematic expectation, not clinical response percentages; Resistance and context are not represented.

Slide 56 · Therapeutic selectivity follows the preexisting repair defect

Normal cells retain HR repair

PARP inhibitor exposure

Homologous recombination still available

Relative sparing versus HR-deficient tumor

Relative therapeutic selectivity is the textbook mechanism; Normal cells are not guaranteed to be unaffected.

Slide 57 · BRCA mutation and PARP sensitivity are related, not synonymous

Germline BRCA status describes inherited susceptibility.

Tumor biallelic loss creates a potential homologous recombination defect.

PARP inhibitors act on a repair vulnerability in malignant cells.

Individual therapeutic response cannot be inferred from gene name alone.

Slide 58 · Genetic testing has both familial and therapeutic applications

Hereditary-risk evaluation

Strong personal or family history may prompt germline evaluation.

Interpret pathogenicity and familial implications.

The source describes focused testing in high-risk contexts.

Cancer-therapy selection

Some breast-cancer patients undergo germline BRCA sequencing.

Pathogenic variants can inform consideration of targeted treatment.

HER2-negative metastatic disease as one example.

This is a textbook-context overview, not a current prescribing or screening guideline.

Slide 59 · A pathology report should separate three kinds of molecular information

Type of information

Example

Interpretation

Inherited susceptibility

Germline BRCA1/BRCA2 pathogenic variant

Risk to carrier and relatives

Tumor biology

Defective homologous recombination pathway

Mechanistic phenotype of cancer

Potential therapeutic vulnerability

PARP-associated synthetic lethality

Possible treatment relevance requiring clinical context

Risk prediction, tumor classification, and drug sensitivity are different clinical inferences.

Slide 60 · Why does a ubiquitous repair defect preferentially affect breast?

BRCA1 and BRCA2 are expressed throughout the body.

Nevertheless, inherited loss preferentially predisposes to breast and certain other epithelial cancers.

The precise cause of this tissue selectivity remains unresolved.

Several nonexclusive mechanistic hypotheses.

Slide 61 · Hypothesis 1: BRCA1 influences luminal differentiation

ER-negative stem / progenitor cell

BRCA1 supports luminal differentiation

ER-positive luminal cell

Proposed biological contribution of BRCA1; Evidence is not presented as a settled explanation of tissue specificity.

Slide 62 · Hypothesis 1: Loss may retain an unstable progenitor pool

BRCA1 deficiency

Disturbed progression toward ER-positive luminal cells

Accumulation of unstable progenitor cells

Increased opportunity for transformation

A model proposed by Robbins, not an experimentally quantified timeline or universal cell-of-origin claim.

Slide 63 · Hypothesis 2: Estrogen may sustain BRCA1-deficient cells

BRCA1-deficient mammary epithelial cell

Estrogen-dependent survival advantage (proposed)

Persistence of genomically unstable cells

Opportunity for additional oncogenic alterations

The textbook explicitly frames the estrogen-survival model as a suggestion rather than established fact.

Slide 64 · Hypothesis 3: Epithelial context influences DNA damage

Breast / ovarian epithelial physiology

Particular types of DNA injury (hypothesized)

Dependence on BRCA-mediated repair

Selective cancer susceptibility

Tissue-specific damage mechanism remains hypothetical in the source; No quantitative rates are asserted.

Slide 65 · Three proposed explanations may cooperate

Hypothesis

Specific proposed link

Evidence status in source

Differentiation

BRCA1 supports ER-negative progenitor → ER-positive luminal progression

Proposed

Hormonal survival

Estrogen may aid BRCA1-deficient cell survival

Suggested

Tissue damage context

Breast / ovary may accumulate BRCA-requiring lesions

Proposed

These hypotheses are not proven to be exhaustive or mutually exclusive.

Slide 66 · Familial and sporadic tumors may converge on repair defects

Inherited origin

Pathogenic germline susceptibility allele precedes tumor development.

Tumor evolution often requires inactivation of the remaining allele.

Family history may be a relevant clue.

Somatically acquired origin

Both alleles can potentially become inactivated through somatic events.

Molecular phenotype may resemble a hereditary repair-deficient tumor.

Absence of a germline defect does not prove an intact tumor repair pathway.

Convergence on pathway failure does not establish identical etiology or management.

Slide 67 · Clinical vignette: Multigenerational breast cancer

A patient reports breast carcinoma in her mother and sister; One relative was diagnosed at a young age. No molecular testing is yet available.

What conclusion is best supported by the family history?

Strong suspicion of an inherited predisposition.

A specific pathogenic BRCA variant cannot yet be assigned.

Slide 68 · Case interpretation: Pedigree is the starting point

A first-degree affected relative and young age strengthen concern for familial susceptibility.

Syndromic and multigene etiologies are possible.

Hereditary risk cannot be converted into a precise genotype from history alone.

Genetic interpretation requires a documented disease-associated variant.

Slide 69 · Clinical vignette: BRCA-associated tumor phenotype

A breast carcinoma has a triple-negative phenotype. The patient also has several relatives affected by breast or ovarian cancer.

Which biological interpretation is reasonable?

BRCA1-associated susceptibility is a consideration.

Triple-negative morphology does not establish a BRCA1 germline variant.

Slide 70 · Case interpretation: Phenotype should not substitute for testing

BRCA1-associated breast cancers are frequently triple-negative.

Other hereditary and nonhereditary pathways can produce the same phenotype.

ER-positive tumors remain compatible with BRCA2-associated predisposition.

Pathology, pedigree, and molecular analysis provide different evidence.

Slide 71 · Clinical vignette: Synthetic lethality

A malignant clone has lost homologous recombination repair function. Nearby nonneoplastic cells retain an intact homologous recombination pathway.

Why could inhibition of PARP-associated repair preferentially injure the tumor?

The tumor has already lost an alternative high-fidelity repair route.

Combined repair impairment can generate lethal DNA damage.

Slide 72 · Case interpretation: Selective toxicity follows repair redundancy

A preexisting homologous recombination defect creates dependency on remaining repair processes.

PARP inhibition increases the burden of unrepaired DNA lesions.

An intact homologous recombination pathway offers normal cells a relative survival advantage.

This establishes a rationale for therapy, not a guarantee of clinical response.

Slide 73 · Mechanistic summary: From germline allele to treatment vulnerability

Inherited susceptibility allele

Acquired tumor suppressor second hit

Homologous recombination deficiency

PARP-associated repair dependence

Synthetic-lethal vulnerability

This pathway particularly illustrates BRCA-related hereditary breast cancer; Not all susceptibility genes act through HR.

Slide 74 · Five distinctions to retain in clinical pathology

Inherited predisposition ≠ inevitable breast cancer.

Autosomal-dominant risk ≠ single-hit cellular tumorigenesis.

BRCA1 phenotype ≠ BRCA2 phenotype.

Germline pathogenic variant ≠ demonstration of tumor repair deficiency.

Drug mechanism ≠ patient-specific treatment response.

Slide 75 · References and source scope

Robbins, Cotran & Kumar. Pathologic Basis of Disease. 11th edition (2026). Chapter 23, The Breast.

Core subsection: “Pathogenesis of Familial Breast Cancer” (pp. 956–957).

Supplemental chapter context: “Pathogenesis of Breast Cancer” and Table 23.3 (printed p. 958 in the supplied extraction).

Diagrams: newly authored, editable schematic teaching illustrations; no diagnostic specimen images are included.

Risk figures and syndromic associations reflect the supplied edition, not independently updated clinical guidelines.