01OverviewDefinition, clinical context and the essential points that orientate the chapter.
Inherited cancer syndromes arise from constitutional variants that reduce tumour suppression, DNA repair or other protective functions across many cells. Examples include hereditary breast and ovarian cancer, Lynch syndrome, familial adenomatous polyposis, Li-Fraumeni syndrome and endocrine tumour syndromes. Penetrance varies by gene, variant, organ, age, sex and environment; carrying a variant increases probability but does not guarantee cancer.
Recognition begins with phenotype rather than a consumer test. Record all primary cancers, age, bilateral or multifocal disease, premalignant burden and the maternal and paternal line separately. Tumour features such as mismatch-repair deficiency can trigger germline assessment, but somatic causes remain possible. The NHS Genomic Medicine Service and National Genomic Test Directory define eligibility and appropriate panels.
Testing should lead to an actionable plan. A confirmed familial variant permits targeted predictive testing, while a negative familial test can reduce certain inherited risks. An uninformative panel does not erase a strong pedigree. Surveillance, risk-reducing surgery and chemoprevention are syndrome-specific and require absolute-risk discussion, fertility and menopause implications, and psychological support.
Key points
- Most cancers are not caused by a single inherited high-penetrance variant, but age, tumour pattern and family history can identify people who need genomic assessment.
- Referral clues include unusually young cancer, multiple primaries, bilateral disease, characteristic rare tumours and several related cancers on one side of a family.
- Take a three-generation pedigree with cancer site, age at diagnosis, ancestry where relevant and results of any previous testing; verify pathology when major decisions depend on it.
- Test an affected relative first when possible because a negative result in an unaffected person may be uninformative.
- A pathogenic or likely pathogenic germline variant can guide surveillance, risk-reducing options, targeted treatment and predictive testing of adult relatives.
- A variant of uncertain significance is not a diagnosis and must not drive prophylactic surgery or predictive family testing.
- Consent covers possible results, limitations, family implications, data use, reproductive choices and the possibility of unexpected information.
- People without an identified variant may still warrant enhanced surveillance when their verified family history remains strongly suggestive.
02AetiologyUnderlying causes, associations and risk factors, with why each one matters.
Pathogenic germline variant
A constitutional variant impairs a tumour-suppressor, DNA-repair or other protective pathway across tissues, increasing the lifetime probability of characteristic cancers.
De novo or inherited origin
The variant may pass through a family or arise de novo in the affected person, so absence of family history does not exclude susceptibility.
Polygenic and unexplained familial risk
Some clustered families reflect many lower-impact variants, shared exposures or undiscovered genes rather than one currently identifiable high-penetrance cause.
03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.
- 1Constitutional vulnerability exists
Every susceptible cell carries one impaired pathway component, reducing the additional somatic events needed for a malignant clone to emerge.
- 2Second hits accumulate
Loss or inactivation of the remaining functional allele can remove tumour suppression or DNA repair in an individual cell lineage.
- 3Tissue-specific penetrance develops
Hormonal environment, organ biology, age and other genes determine where and when cancers arise despite the variant being present throughout the body.
- 4Genomic instability accelerates
Repair syndromes increase mutation accumulation, creating multiple primary cancers and characteristic tumour signatures that can also influence treatment response.
04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.
Diagnosis substantially earlier than the usual population pattern raises inherited susceptibility, especially with rare histology or another primary.
Bilateral breast cancer, colorectal and endometrial cancer, multiple endocrine tumours or repeated polyps can form a recognisable syndrome pattern.
Related cancers across successive generations on the same lineage may fit dominant inheritance, while small families and sex distribution can conceal it.
Mismatch-repair loss, characteristic mutational signature or another validated tumour feature can justify germline testing but is not itself constitutional proof.
A documented pathogenic variant in a blood relative permits targeted predictive testing with a clearer interpretation than broad screening.
05InvestigationsWhat to request, why it matters and how to interpret it.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Three-generation pedigreeFirst step - Why
- Estimate whether personal and family pattern meets genomic referral criteria.
- Interpretation and limitations
- Record exact cancer type, age, lineage, multiple primaries and unaffected relatives; verify pathology or certificates when feasible and consequential.
- 02
Tumour biomarker testing - Why
- Identify a phenotype associated with inherited susceptibility and guide treatment.
- Interpretation and limitations
- Interpret protein loss or sequencing with pathology and somatic explanations; abnormal tumour findings often require constitutional confirmation.
- 03
Germline multigene or targeted test - Why
- Identify a pathogenic constitutional variant under the national test directory.
- Interpretation and limitations
- Choose affected-first and syndrome-directed testing where possible; explain uncertain, incidental and technically undetected variants before sampling.
- 04
Predictive familial-variant test - Why
- Determine whether an adult relative carries a known pathogenic family variant.
- Interpretation and limitations
- Pre-test counselling clarifies possible positive and true-negative results, surveillance consequences and confidentiality; testing minors depends on childhood actionability.
- 05
Syndrome-specific baseline assessment - Why
- Detect existing disease and plan future surveillance after diagnosis.
- Interpretation and limitations
- Organ tests and intervals follow current specialist protocols; broad whole-body testing is not automatically appropriate for every syndrome.
06Differential diagnosisRealistic alternatives and the features that help distinguish them.
Sporadic early cancer
Cancer can occur young without a high-penetrance germline variant, particularly when tumour and pedigree features do not form a recognised syndrome.
Shared environmental exposure
Smoking, infection, occupation or another familial exposure can cluster cancer without Mendelian inheritance and requires its own prevention strategy.
Polygenic familial aggregation
Multiple common variants can raise risk across a family without producing a single-gene pattern or an informative standard panel result.
Incorrect family history
Benign tumours, metastases recorded as new primaries and uncertain ages can falsely create a syndrome pattern until diagnoses are verified.
07ManagementImmediate care, first-line treatment, alternatives and escalation.
01RecogniseBuild and verify inherited-risk evidenceFirst stepPersonal or family cancer features suggest more than sporadic risk.+
- 1Take a three-generation pedigree and obtain the existing pathology or family genetic report rather than relying on a remembered gene name.
- 2Check the current National Genomic Test Directory or specialist criteria and refer with the features that meet them.
- 3Address immediate cancer treatment separately; urgent therapeutic biomarker testing may run in parallel with fuller genetics assessment.
02TestUse the most informative personGenomic assessment confirms that germline testing is appropriate.+
- 1Where possible, test an affected relative whose tumour and age best represent the suspected syndrome, after informed consent.
- 2Use a targeted familial test when a pathogenic variant is already documented; use an indicated panel when the causal gene is unknown.
- 3Return pathogenic, negative and uncertain results with their distinct meanings and confirm who owns reclassification and family communication.
03ActTranslate a confirmed risk into careA pathogenic variant or strongly suggestive uninformative pedigree remains after testing.+
- 1Create an organ-specific surveillance plan and discuss risk-reducing surgery or medicine only where evidence supports the individual's absolute risk.
- 2Offer cascade testing through approved family-contact processes while preserving the patient's confidentiality and relatives' right not to know.
- 3Include reproductive options, treatment implications, menopause or fertility effects and psychological support, reviewing the plan as guidance evolves.
08ComplicationsImportant consequences, why they occur and why they matter clinically.
Multiple primary cancers
Persisting constitutional risk can produce new independent cancers after successful treatment of the first, requiring lifelong syndrome-specific surveillance.
Cancer in relatives
A pathogenic familial variant may place blood relatives at substantial preventable risk if cascade testing and surveillance are not offered.
Preventive-treatment harm
Risk-reducing surgery or chemoprevention can cause infertility, early menopause, bleeding or other morbidity when benefits and timing are not individualised.
Psychological and family burden
Uncertainty, survivor guilt, communication difficulties and differing preferences about testing can strain wellbeing and relationships across generations.
09Monitoring and follow-upTreatment response, safety checks and longer-term review.
- Maintain a verified pedigree and update new family cancers, deaths and genetic results because eligibility and interpretation can change.
- Track completion of syndrome-specific surveillance rather than merely recording that advice was given.
- Review variant classification through the responsible genetics service; do not reinterpret a laboratory result from ungoverned internet databases.
- Monitor physical and psychological consequences of surveillance, risk-reducing surgery, early menopause and reproductive decisions.
- Ensure cancer teams know treatment-relevant inherited findings while sharing only the family information needed for care.
10Special situationsVariants, exceptions and circumstances that change the usual approach.
Paternal history counts
Dominant cancer variants pass through any sex, so breast or ovarian patterns on the father's side remain clinically relevant.
Affected-first is powerful
A negative panel in an unaffected relative cannot exclude a family syndrome when no affected person's causal variant is known.
Tumour and germline differ
Mismatch-repair loss or a pathogenic tumour variant can arise somatically and needs the appropriate constitutional confirmation pathway.
VUS is not actionable
Uncertain variants are expected during broad testing and should not change surgery, surveillance or relatives' care outside evidence review.
Negative can remain high risk
Testing technology and gene knowledge are incomplete; a compelling verified pedigree may still justify clinical surveillance.
11Common pitfallsFrequent interpretation and management errors.
- 01
Ignoring the paternal lineage in clinical practice.
- 02
Recording cancer without age or primary site.
- 03
Testing an unaffected relative first without reason.
- 04
Treating a tumour variant as germline proof.
- 05
Operating because of a variant of uncertain significance.
- 06
Assuming a negative panel removes pedigree risk.
- 07
Sharing relatives' information beyond necessary care.