Genetic Testing for Cancer: Who Needs It and How Can It Help? By Dr. M. G. Giriyappagoudar Senior Radiation Oncologist, HCG Cancer Centre, Hubli | North Karnataka

 

When we hear the word “genetic testing,” many people think:

“Does this mean I have cancer?”

Not necessarily.

Genetic testing can help us understand whether a person has inherited a change in a gene that can increase the risk of developing certain cancers.

Only about 5–10% of all cancers are estimated to be caused by inherited harmful genetic changes. Therefore, not everyone needs genetic testing.

What is genetic testing for cancer?

Our body contains genes that act like instructions for our cells.

Sometimes, a person is born with a harmful change in one of these genes. This change may increase the chance of developing certain cancers during life.

A genetic test can look for these inherited changes, usually using a blood or saliva sample.

This is called germline genetic testing.

But there is another type of genetic testing

Tumor genetic testing looks at DNA changes inside cancer cells. It is mainly used to help doctors understand the cancer and sometimes select targeted treatment.

Germline testing = inherited cancer risk

Tumor testing = changes in the cancer itself

They are different tests and one does not automatically replace the other.

Who should consider genetic counselling?

Genetic counselling should particularly be considered when there is a strong personal or family history of cancer.

Some important warning signs are:

🚩 1. Cancer at a young age

For example, breast cancer at a young age or colorectal cancer diagnosed before 50.

🚩 2. Several family members with cancer

Especially when multiple close relatives have similar or related cancers.

🚩 3. Breast and ovarian cancer in the same family

This can sometimes suggest inherited BRCA-related cancer risk.

🚩 4. Colon and endometrial cancer in a family

This may raise suspicion of Lynch syndrome.

🚩 5. A person develops more than one primary cancer

For example, breast cancer followed by another unrelated primary cancer.

🚩 6. Cancer in both paired organs

For example, cancer occurring in both breasts or both kidneys.

🚩 7. Rare cancers

For example, male breast cancer.

🚩 8. A known genetic mutation in the family

If one family member has a confirmed inherited cancer-related mutation, other blood relatives may need counselling and targeted testing.

🚩 9. Certain cancers where germline testing is routinely recommended

Current guidance recommends inherited genetic testing for people with cancers such as:

  • Triple-negative breast cancer
  • Ovarian cancer
  • Pancreatic cancer
  • Colorectal cancer diagnosed before age 50
  • Metastatic prostate cancer
  • Male breast cancer

The exact criteria can vary according to the cancer type and the guideline being followed.

What genetic tests are commonly done?

There is no single “cancer gene test.”

Depending on the patient's history, doctors may recommend a multigene panel.

Some important genes and syndromes include:

BRCA1 and BRCA2

Associated particularly with increased risks of:

  • Breast cancer
  • Ovarian/fallopian tube cancer
  • Pancreatic cancer
  • Prostate cancer

Lynch syndrome genes

Usually include genes such as:

  • MLH1
  • MSH2
  • MSH6
  • PMS2
  • EPCAM

These are associated with increased risks of colorectal, endometrial and several other cancers.

Other genes

Depending on the family history, testing may include genes such as:

TP53, PALB2, ATM, CHEK2, PTEN, CDH1, STK11 and others.

The important point is:

Do not choose a genetic test simply because it is available.

The appropriate test should be selected after reviewing the person's cancer history and family history. Multigene panels are commonly used when no specific family mutation is already known.

How can genetic testing help a common person?

Genetic testing is not only about finding a gene.

It can potentially help an entire family.

1. Earlier cancer screening

If a harmful inherited mutation is found, doctors may recommend earlier or more frequent screening for particular cancers.

2. Prevention

For some high-risk genetic conditions, specific risk-reducing measures may be considered.

3. Treatment decisions

For a person who already has cancer, finding an inherited mutation can sometimes provide information that helps guide treatment.

4. Information for children and siblings

If a harmful inherited mutation is identified, blood relatives may be offered targeted testing for the same mutation.

This is sometimes called cascade testing.

5. Understanding the family history

Sometimes a family may have wondered for years:

“Why are so many people getting cancer in our family?”

Genetic counselling and testing may provide an explanation in some families.

Does a positive genetic test mean I will definitely get cancer?

No.

A positive test usually means that the person has an inherited genetic change associated with an increased risk of particular cancers.

It does not mean that cancer is certain to develop.

Similarly, a negative test does not mean that a person can never develop cancer.

Cancer risk is influenced by many factors, including:

  • Age
  • Family history
  • Lifestyle
  • Tobacco and alcohol exposure
  • Environment
  • Hormonal factors
  • Other genetic factors

Therefore, genetic results should always be interpreted along with the person's complete medical and family history.

What is genetic counselling?

Genetic counselling is a discussion with a trained genetic counsellor, medical geneticist, oncologist or other appropriately trained healthcare professional.

Before testing, they may discuss:

Your cancer history → Your family history → Possible inherited risk → Appropriate test → Benefits and limitations → Possible results → What the result could mean for your family

Counselling is important because genetic reports can sometimes be complicated.

For example, a report may show a VUS – Variant of Uncertain Significance.

A VUS does not mean that you have a cancer-causing mutation.

It means that the significance of that genetic change is currently uncertain.

This is one reason why genetic testing should not be interpreted without appropriate medical guidance.

A simple rule for families

Ask yourself these five questions:

1. Did anyone in my family develop cancer at a young age?

2. Do several close relatives have cancer?

3. Are there breast, ovarian, pancreatic or prostate cancers in my family?

4. Are there colon or endometrial cancers in my family?

5. Has anyone in my family already been found to have a cancer-related genetic mutation?

If the answer to one or more is YES, discuss your family history with your oncologist or a genetic counsellor.

One important message

Don't panic. Don't test blindly.

A genetic test is a medical test, not a routine health package.

You do not need every genetic test available in the market.

The right approach is:

Family history → Genetic counselling → Appropriate testing → Correct interpretation → Personalised screening/prevention

And whenever possible, when a family member already has cancer, testing often begins with the affected family member, because this can provide more useful information for the rest of the family.

Final message

Cancer is not always simply a matter of “luck.”

In some families, an inherited genetic change can increase cancer risk.

Finding that risk early can give a family something extremely valuable:

KNOWLEDGE.

And knowledge can lead to:

Earlier screening.
Better prevention.
More informed treatment.
And better information for the next generation.

If you or your family have a strong history of cancer, speak to your oncologist about whether genetic counselling and genetic testing may be appropriate.

Dr. M. G. Giriyappagoudar

Senior Radiation Oncologist
HCG Cancer Centre, Hubli
North Karnataka

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