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Most cancers are not caused by inherited genetic changes. However, in some patients, an inherited genetic predisposition plays a crucial role in the development of the disease.
According to Dr Monika Koudová, MBA, a clinical geneticist, Head of the GENNET Genetics Programme and Medical Director of GNTlabs by GENNET, hereditary factors can contribute to almost any type of cancer.
In clinical genetics, the most frequently investigated hereditary cancer predispositions involve breast, ovarian, colorectal, endometrial, pancreatic, prostate, gastric and kidney cancers. Melanoma and certain rare or endocrine tumours may also have a significant hereditary component.
The decision to recommend genetic testing is therefore based not only on the specific cancer diagnosis but also on the wider clinical context, particularly the patient's age at diagnosis, the precise histological type of tumour and their family medical history.
When Should You Be Concerned?
The following factors may raise suspicion of an inherited cancer predisposition:
- Cancer diagnosed at an unusually young age.
- The same or related types of cancer affecting several family members.
- Cancer occurring across multiple generations on the same side of the family.
- Multiple independent primary cancers in one individual.
- Cancer affecting both sides of a paired organ, or recurrent cancer in such an organ.
- A rare type of tumour.
- Cancer occurring in a person for whom it is unusual, such as breast cancer in men.
- A characteristic combination of different cancers on the same side of the family.
However, several cases of cancer within one family do not necessarily indicate a hereditary cancer syndrome. Cancer is relatively common, and some cases may occur independently.
A clinical geneticist therefore evaluates the wider family history, typically covering at least three generations, while also considering the relationships between affected relatives.
Sometimes a Single Case Is Enough
Genetic testing is not reserved exclusively for families in which several relatives have developed cancer. For certain diagnoses, a single case may be sufficient to justify testing, depending primarily on the type of cancer and the patient's age at diagnosis.
Under the clinical criteria described here, genetic testing is recommended regardless of age or family history for all patients with exocrine pancreatic cancer, women with epithelial ovarian or fallopian tube cancer or primary peritoneal cancer, and men diagnosed with breast cancer.
For women, a breast cancer diagnosis at the age of 60 or younger is itself an indication for genetic testing. For most other cancer types, diagnosis at the age of 50 or younger may also warrant testing.
The precise criteria for genetic testing are continually updated as scientific knowledge advances. Someone who did not meet the criteria several years ago may therefore qualify today.
If genetic testing was not previously recommended or considered, it may be worthwhile discussing the situation again with a clinical geneticist.
Both Sides of the Family Matter
Inherited cancer predispositions can be passed down through both women and men. When assessing family history, information about the maternal and paternal sides of the family is therefore equally important.
Before a genetic consultation, it is helpful to gather as much accurate information as possible about the medical diagnoses of parents, grandparents, siblings, aunts and uncles.
Where available, medical records can significantly improve the accuracy of the assessment.
Who Should Be Tested First in the Family?
Whenever possible, genetic testing should begin with a family member who has already been diagnosed with cancer.
Testing an affected individual offers the greatest likelihood of identifying a specific inherited pathogenic variant, commonly referred to as a mutation, that may have contributed to the development of their cancer.
If such a variant is identified, other family members can then undergo targeted genetic testing for that specific familial variant.
If the affected relative has died, testing is generally recommended first for their closest living relative, such as a child or sibling.
What Does a Positive Genetic Test Result Mean?
A positive genetic test result does not mean that someone currently has cancer or will inevitably develop it.
Instead, it indicates the presence of an inherited genetic predisposition that increases the likelihood of developing certain types of cancer.
The level of risk varies depending on the gene and the specific pathogenic variant identified, as well as the individual's age, sex and other factors.
Knowing about an inherited predisposition makes it possible to develop a personalised cancer prevention and surveillance plan. This may include:
- Starting screening and surveillance at a younger age.
- Shorter intervals between examinations.
- More sensitive imaging techniques, such as breast magnetic resonance imaging (MRI).
- More frequent colonoscopies.
- Surveillance of other organs associated with the specific hereditary cancer syndrome.
- In selected cases, preventive medication or risk-reducing surgery.
The aim is not to screen the entire body indiscriminately for cancer, but to focus preventive measures on the organs in which the identified genetic variant is known to increase cancer risk.
Genetic Predisposition Does Not Determine Your Future
An inherited genetic variant cannot be eliminated through lifestyle changes. However, a healthy lifestyle can influence certain aspects of an individual's overall cancer risk.
General recommendations include avoiding smoking, limiting alcohol consumption, maintaining a healthy body weight, exercising regularly, protecting the skin from ultraviolet (UV) radiation and receiving recommended vaccinations.
For individuals with certain hereditary predispositions, more specific recommendations may apply.
However, a healthy lifestyle is not a substitute for an individualised cancer surveillance programme.
It is equally important to understand that if someone carrying a pathogenic genetic variant develops cancer, it is not their fault or the result of a personal failure.
A Negative Genetic Test Result Does Not Always Mean the Same Thing
A negative genetic test result can have two very different interpretations.
If a specific pathogenic variant has already been identified within a family and testing confirms that an individual has not inherited it, this is considered a true negative result.
In this situation, the increased cancer risk associated with that particular familial variant does not apply to the individual. However, they remain subject to the background cancer risk present in the general population, making routine preventive examinations and population screening programmes important.
A different situation arises when no specific pathogenic variant has yet been identified within the family because previous genetic investigations have not detected one.
In such cases, a negative result does not completely exclude an inherited or familial cancer predisposition.
The underlying cause may involve a gene that has not yet been identified, a type of genetic alteration that cannot be detected by the testing method used, or a genetic variant whose clinical significance cannot currently be reliably determined.
For this reason, recommendations for cancer prevention and surveillance should continue to take family history into account, even after a negative genetic test result.
What Does the Result Mean for Children and Other Relatives?
For most hereditary cancer syndromes, each child of a person carrying a pathogenic variant has a 50% chance of inheriting it.
This probability applies independently to each child. It does not mean that exactly one out of two children will necessarily inherit the variant.
If a child has not inherited the familial variant, they do not carry the increased inherited cancer risk associated with that particular predisposition.
If they have inherited it, an appropriate prevention and surveillance programme can be established.
Genetic testing for hereditary cancer predispositions associated exclusively with adult-onset cancers is generally deferred until adulthood.
Exceptions include syndromes for which preventive surveillance should begin during childhood or adolescence.
Blood or Saliva: Which Is Better for Genetic Testing?
Inherited genetic predispositions can be investigated using different types of biological samples.
Provided that a sufficient quantity of high-quality DNA is obtained, genetic testing using saliva can be just as accurate as testing using blood.
However, blood samples are often preferred because they generally provide a reliable amount of high-quality DNA.
There are also exceptions.
For example, following a bone marrow or haematopoietic stem cell transplant, a patient's blood may predominantly contain the donor's DNA.
In such cases, an alternative sample, such as hair follicles, may be used following specialist assessment.
Why You Should Be Cautious About Online DNA Tests
Commercial genetic tests can differ significantly in their scope and quality.
Some tests performed by accredited clinical laboratories may be reliable. However, many commercially available direct-to-consumer testing kits analyse only a limited number of preselected genetic variants.
A negative result from such a test therefore does not necessarily exclude an inherited cancer predisposition.
If a commercial test identifies a potentially serious genetic finding, the result should not be used as the sole basis for medical decisions.
The finding should be confirmed through appropriate clinical testing in an accredited laboratory and discussed with a clinical geneticist.
Professional genetic counselling is important both before and after testing.
A clinical geneticist can help determine the most appropriate testing strategy, explain its capabilities and limitations, and interpret the results in the context of the patient's personal and family medical history.
Does Cancer Genetic Testing Automatically Check for Other Inherited Diseases?
Usually not.
Most laboratories investigating hereditary cancer predispositions analyse only the genes included in the relevant hereditary cancer gene panel.
A negative result therefore provides no information, for example, about inherited predispositions to cardiovascular disease.
Whole-exome or whole-genome sequencing may also identify so-called secondary findings — medically significant genetic variants unrelated to the original reason for testing.
Whether these findings are actively investigated and disclosed depends on the type of test, the laboratory's policies and the patient's informed consent.
Should Everyone Undergo Preventive Genetic Testing?
Routine, comprehensive genetic testing of all healthy individuals is not currently recommended as a standard approach.
Genetic testing offers the greatest benefit when personal or family medical history, a young age at cancer diagnosis, a rare tumour type or another clinical factor suggests a possible inherited risk.
However, the absence of a known family history of cancer does not completely rule out a hereditary predisposition.
A family may be small, some relatives may have died young from unrelated causes, a pathogenic variant may have been passed down through a parent who has never developed cancer, or the variant may have arisen spontaneously.
The most practical approach is to understand your family's medical history, keep this information up to date and attend routine health checks and recommended cancer screening appointments.
If you are interested in genetic testing despite having no obvious family history of cancer, it is advisable to arrange a consultation with a clinical geneticist first.
What Happens During Genetic Testing, and How Long Do Results Take?
The first step is a genetic consultation.
During the appointment, the clinical geneticist reviews the patient's personal and family medical history, constructs a family pedigree and assesses whether genetic testing is appropriate and, if so, which type of testing would be most suitable.
Depending on the clinical indication, laboratory analysis may involve a comprehensive panel of genes associated with hereditary cancer syndromes or targeted testing for a specific pathogenic variant already identified within the family.
The turnaround time depends on the scope and urgency of the testing.
Results from a comprehensive hereditary cancer gene panel may take approximately two months.
Targeted testing for a known familial variant is generally faster, with results usually available within two weeks.
Priority testing may be indicated when the result is expected to have an immediate impact on planned surgery or treatment. In such cases, results are typically available within two to three weeks.
Is Genetic Testing Covered by Health Insurance?
In the Czech Republic, genetic testing is covered by public health insurance when the established clinical eligibility criteria are met and the test is indicated by a clinical geneticist.
Individuals who do not meet these criteria may still undergo genetic testing on a self-funded basis following a specialist consultation.
The cost depends on the number and range of genes analysed and the healthcare provider performing the test.
Understanding Your Risk Means You Can Act Early
A genetic test result is not a prediction of the future.
It provides information that allows cancer prevention and surveillance to be tailored to an individual's actual level of risk.
The findings may also have important implications beyond the person being tested, potentially benefiting their siblings, children and parents.
Concerned About Your Family's Hereditary Cancer Risk?
Our specialists will review your personal and family medical history, assess your individual risk and recommend the most appropriate next steps.
Medically Reviewed By
Dr Monika Koudová, MBA
Head of the GENNET Genetics Programme and Medical Director of GNTlabs by GENNET.
Dr Koudová has more than 25 years of experience in clinical genetics and genetic laboratory methods. She is a member of the Executive Committee of the Czech Society of Medical Genetics and Genomics (ČLS JEP) and a member of the American Society of Human Genetics.
Editorial Note
This article is based on an online Q&A session held on 18 September 2026 between Dr Monika Koudová, MBA, and readers of iDNES.cz, together with a subsequent editorial article.
The article has undergone expert review to ensure that the information on genetic testing eligibility criteria, insurance coverage, gene panel scope, turnaround times and self-funded testing costs is up to date.
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