Cancer Genetic Testing: Essential Information for Patients

Cancer Genetic Testing: What Newly Diagnosed Cancer Patients Need to Know

a couple of weeks ago
/ cancer
/ By David Emerson

Cancer Genetic Testing: What Newly Diagnosed Cancer Patients Need to Know. If you have just been diagnosed with cancer, genetic testing may be one of the most important questions to ask your oncology team—but many patients don’t know to ask.

A cancer diagnosis can feel overwhelming. Your immediate concerns are probably staging, treatment options, surgery, chemotherapy, radiation, immunotherapy, side effects, and prognosis.

But there is another question that deserves a place near the top of your list:

Could genetic testing tell me something important about my cancer, my treatment options, or my family’s cancer risk?

The answer is sometimes yes.

Genetic testing can identify inherited changes in genes that increase cancer risk. Testing the tumor itself can identify genetic changes that may help doctors select cancer treatments. These are different tests, and understanding the difference is important.

The National Cancer Institute estimates that approximately 5% of inherited genetic changes cause 10% of all cancers.

For some newly diagnosed cancer patients, genetic information can influence treatment decisions. For others, it can identify an inherited cancer risk that may be important to children, siblings, parents, and other blood relatives.

Yet genetic testing remains underused.

If you undergo genetic testing, you may wonder What does a Positive Cancer Genetic Test Mean?

I am a long-term survivor of an incurable blood cancer called multiple myeloma. I have been amazed by the continual advancements in diagnostic testing that I have witnessed since my diagnosis in 1994. I consider cancer genetic testing to be yet another advancement in diagnostic testing.

Scroll down the page and post a question or a comment if there’s anything you’d like to know about cancer genetic testing.

Good luck,

David Emerson

Concepts Central to Managing Your Cancer-

Newly Diagnosed With Cancer? Ask About These 5 Tests

1. Pathology testing → What kind of cancer is it?
2. Staging tests → How far has it spread?
3. Biomarker/tumor genomic testing → What is driving the cancer?
4. Germline genetic testing → Did I inherit a cancer-risk gene?
5. Family-history assessment → Could my diagnosis have implications for relatives?

What Is Cancer Genetic Testing?

“Cancer genetic testing” is actually an umbrella term for several different types of testing.

The two most important categories for cancer patients are:

Germline genetic testing
Tumor genomic testing, also called biomarker testing or somatic testing

They answer different questions.

Germline Genetic Testing: “Was I Born With a Cancer-Related Gene Change?”

Germline testing examines DNA that you inherited from your parents.

Usually, the sample comes from blood or saliva.

A germline test looks for inherited genetic variants that can increase the risk of developing certain cancers.

Examples include inherited changes in:

BRCA1
BRCA2
PALB2
TP53
MLH1
MSH2
MSH6
PMS2
APC
ATM
CHEK2
and other cancer-associated genes.

A harmful inherited variant does not mean that a person will definitely develop cancer. It means that the person’s risk may be higher than average.

Because an inherited variant can be passed from parent to child, this information may matter for the entire family.

Tumor Genetic Testing: “What Is Driving My Cancer?”

Tumor genomic testing asks a different question:

What genetic changes are present inside my cancer cells?

Cancer cells accumulate genetic changes during a person’s lifetime. These changes can help cancer cells grow, survive, and spread.

Testing the tumor can sometimes identify biomarkers that help doctors determine which treatments may be appropriate.

For example, certain genetic or molecular characteristics can make a cancer more likely to respond to a targeted therapy or immunotherapy.

The NCI calls this type of testing biomarker testing, and it may also be called:

tumor profiling
molecular profiling
genomic profiling
tumor genetic testing
somatic testing

Importantly, tumor testing and inherited genetic testing are not interchangeable.

Why Should a Newly Diagnosed Cancer Patient Care About Genetic Testing?

There are several reasons.

1. Genetic Testing May Affect Your Treatment

Some inherited genetic changes can influence treatment decisions.

For example, inherited changes in BRCA1 or BRCA2 can be relevant to treatment decisions involving certain breast, ovarian, pancreatic, and prostate cancers.

Other genetic characteristics—including changes involving DNA mismatch repair—can influence whether certain immunotherapies may be appropriate.

The American Society of Clinical Oncology (ASCO) notes that germline testing can identify inherited variants that may affect the use of targeted cancer therapies and can provide information about future cancer risks.

This creates an important question for newly diagnosed patients:

Is there a genetic characteristic of my cancer that could change my treatment options?

2. Genetic Testing May Identify Your Risk of Another Cancer

A cancer diagnosis doesn’t necessarily mean that your current cancer is the only cancer risk you need to think about.

An inherited cancer-predisposition gene may increase the risk of developing more than one type of cancer.

Knowing about an inherited mutation may allow you and your doctors to develop a more appropriate surveillance and prevention plan.

That could mean:

earlier screening
more frequent screening
different screening tests
preventive surgery in selected circumstances
monitoring for additional cancers

The appropriate strategy depends on the specific gene, the person’s cancer history, family history, age, and other factors.

3. Your Genetic Information May Be Important to Your Family

This is one of the most overlooked benefits of genetic testing.

Suppose you are diagnosed with cancer and genetic testing identifies a harmful inherited variant.

Your children, siblings, and parents may have a chance of carrying the same variant.

That does not mean that they have cancer.

It means they may have inherited an increased risk of developing certain cancers.

That information could allow family members to discuss genetic counseling and appropriate cancer screening with their own physicians.

In other words:

Your genetic test may provide information that could help protect your family.

The NCI emphasizes that genetic testing can provide potentially important information to blood relatives.

4. Your Family History May Be More Important Than You Think

When you are diagnosed with cancer, your oncologist may ask about your family history.

Don’t dismiss the question.

ASCO recommends that patients have a cancer family history recorded, including cancers occurring in first- and second-degree biological relatives and, when possible, information such as the type of cancer and age at diagnosis.

Before your oncology appointment, try to find out:

Which relatives have had cancer?
What type of cancer did they have?
At what age were they diagnosed?
Did anyone have more than one primary cancer?
Has anyone had genetic testing?
Was a harmful genetic variant found?
Are there cancers on both your mother’s and father’s sides of the family?

You don’t need a perfect family tree.

Even incomplete information can be useful.

Who Should Consider Cancer Genetic Testing?

This is one of the most important questions—and the answer is changing.

Historically, genetic testing was often offered only to patients whose personal or family history suggested a hereditary cancer syndrome.

Today, professional guidelines recommend germline testing for substantially broader groups of cancer patients.

The NCI identifies several cancers for which clinical practice guidelines recommend genetic testing, including:

triple-negative breast cancer
ovarian cancer
pancreatic cancer
colorectal cancer diagnosed before age 50
metastatic prostate cancer
male breast cancer

Other personal and family-history patterns can also warrant genetic evaluation.

ASCO’s germline-testing guideline similarly emphasizes that eligibility depends on the patient’s cancer type, personal history, family history, and other circumstances.

The important point:

Don’t assume you are not eligible for genetic testing simply because nobody in your family has had cancer.

Some cancer-associated inherited variants can be present even when the family history is limited or unclear.

What Is a Genetic Testing Panel?

Instead of testing one gene at a time, doctors can use a multigene panel.

A panel examines multiple genes simultaneously.

For example, a breast cancer panel might examine genes such as BRCA1, BRCA2, PALB2, TP53, PTEN, and others.

The appropriate panel depends on the person’s cancer type and personal and family history.

ASCO recommends offering multigene panel testing when more than one gene is relevant to a patient’s situation.

More testing, however, isn’t automatically better.

Larger panels can increase the possibility of finding a genetic change whose significance is unclear.

That’s why genetic counseling and appropriate interpretation are important.

What Does a Positive Genetic Test Mean?

A positive test generally means that a harmful or potentially harmful inherited genetic variant has been identified.

It does not necessarily mean:

“I am going to get another cancer.”

Instead, the result may indicate that your risk for certain cancers is higher than average.

Depending on the gene involved, doctors may recommend additional screening, prevention strategies, or changes in treatment.

A positive result can also trigger an important conversation with family members.

What Does a Negative Genetic Test Mean?

A negative test can be reassuring—but it does not necessarily mean that you have no inherited cancer risk.

This is a critical distinction.

Genetic testing cannot identify every possible cause of cancer.

A person may still have an increased cancer risk because of:

family history
environmental exposures
lifestyle factors
genetic factors that current testing cannot detect
genes that have not yet been identified
combinations of genetic variants

ASCO specifically notes that a negative germline test does not necessarily eliminate hereditary cancer risk when the personal or family history remains suggestive.

Therefore:

A negative genetic test does not automatically erase your family history.

What Is a Variant of Uncertain Significance?

Sometimes genetic testing identifies a variant of uncertain significance, commonly abbreviated VUS.

This means that researchers have found a genetic change but do not yet know whether it increases cancer risk.

A VUS is not the same thing as a positive genetic test.

Patients should be particularly careful about making major medical decisions based solely on a VUS.

Genetic counselors and qualified healthcare professionals can help explain what the result means and whether anything should actually change because of it.

The NCI lists uncertainty surrounding VUS results as one of the potential downsides of genetic testing.

Can a Tumor Test Find an Inherited Mutation?

Sometimes.

But this is where cancer patients need to be careful.

A tumor test may identify a genetic variant that could also be inherited.

If that happens, doctors may recommend a separate germline test to determine whether the variant is actually present in the person’s inherited DNA.

ASCO specifically recommends germline testing in certain situations when tumor testing identifies potentially inherited pathogenic variants.

And ASCO emphasizes an important point:

Tumor testing should not be used as a substitute for indicated germline testing.

In its guideline review, ASCO noted that tumor testing can miss a proportion of germline pathogenic variants.

When Should Genetic Testing Be Done?

For a newly diagnosed cancer patient, genetic testing should be considered early enough to potentially influence treatment decisions.

That doesn’t necessarily mean every cancer patient needs every possible genetic test.

Instead, ask your oncology team:

“Should I have germline genetic testing?”

And:

“Should my tumor undergo genomic or biomarker testing?”

These are two different questions.

For some cancers, the answers may be especially important before treatment decisions are finalized.

Questions to Ask Your Oncologist

Consider bringing these questions to your next appointment:

Should I have inherited cancer-risk genetic testing?
Should I meet with a genetic counselor?
Does my cancer type qualify me for germline testing?
Does my family history suggest an inherited cancer syndrome?
Should my tumor undergo genomic or biomarker testing?
Could genetic or genomic testing change my treatment options?
Could the results affect my risk of developing another cancer?
Could the results be important for my children, siblings, or parents?
What genetic testing panel would you recommend and why?
Will my health insurance cover the testing?
What happens if the result is positive?
What happens if the result is negative?
What happens if the result is a variant of uncertain significance?
Who will explain the results to me?

What About Genetic Counseling?

Genetic counseling can be particularly valuable because genetic testing isn’t simply a matter of drawing blood and receiving a yes-or-no answer.

A genetic counselor can help you understand:

why testing is being recommended
which genes are being tested
what a positive result could mean
what a negative result could mean
what a VUS means
what the results could mean for relatives
possible screening or prevention strategies
insurance and privacy considerations

The NCI recommends discussing inherited cancer-risk testing with a healthcare provider or genetic counselor when appropriate.

What About At-Home Genetic Tests?

Consumer genetic testing can be tempting because it is convenient.

But cancer-risk testing is different from recreational ancestry testing.

The NCI cautions that direct-to-consumer genetic tests have important limitations and generally should not be relied upon as a substitute for clinically appropriate genetic evaluation.

A negative result from a limited consumer test does not necessarily mean that you do not carry another cancer-associated genetic variant.

For someone who has already been diagnosed with cancer, discuss clinically appropriate testing with your oncology team or a genetic counselor.

How Much Does Cancer Genetic Testing Cost?

Cost varies according to:

the type of test
the number of genes tested
the laboratory
insurance coverage
whether testing is considered medically necessary
whether genetic counseling is included

The NCI notes that health insurance typically covers genetic counseling and testing considered medically necessary, although patients should confirm coverage and potential costs with their healthcare provider and insurer.

Don’t assume that testing is unaffordable before asking.

Genetic Testing and Privacy

Genetic information is uniquely personal.

It can contain information about you and potentially about biological relatives.

Before testing, ask:

Who will have access to my results?
How will the laboratory store my genetic information?
Will my results be placed in my medical record?
Can my information be used for research?
What privacy protections apply?

These questions are particularly important when considering direct-to-consumer genetic testing.

The Bigger Picture: Genetic Testing Is Part of Personalized Cancer Care

Cancer treatment is moving away from the idea that every patient with the same cancer should receive the same treatment.

Two people can have the same cancer diagnosis but very different tumors—and very different genetic risks.

Genetic and genomic testing can provide another layer of information.

Think of cancer care as a series of questions:

What cancer do I have?

↓

How advanced is it?

↓

What is causing it to grow?

↓

Does my tumor have biomarkers that could influence treatment?

↓

Do I carry an inherited genetic change that affects my cancer risk or treatment?

↓

Could this information be important to my family?

That is the potential value of cancer genetic testing.

Genetic Testing Does Not Replace Your Oncologist

Genetic testing is a tool—not a treatment.

A test result should be interpreted in the context of:

your cancer diagnosis
stage
pathology
family history
other medical conditions
previous treatments
current treatment options
clinical guidelines

Do not change cancer treatment, screening, or preventive care based solely on a genetic test report without discussing the result with an appropriately qualified healthcare professional.

Bottom Line: Ask About Genetic Testing After a Cancer Diagnosis

If you have recently been diagnosed with cancer, you may have dozens of questions.

Genetic testing may not be the first thing that comes to mind.

It should be on the list.

The most important distinction to remember is:

Germline testing asks whether you inherited a cancer-related genetic change. Tumor genomic testing asks what genetic changes are present in your cancer.

Sometimes you need one.

Sometimes you need both.

And sometimes the information can influence treatment, cancer surveillance, and the health decisions of your family members.

So consider asking your oncology team:

“Should I have germline genetic testing, tumor genomic testing, or both—and could the results change my treatment or my family’s cancer risk?”

That single question could open an important new conversation about your cancer care.

PeopleBeatingCancer Evidence Rating

Evidence Rating: High

The distinction between germline testing and tumor genomic/biomarker testing is well established by the National Cancer Institute. Professional oncology guidance, including ASCO’s germline-testing guideline, supports appropriate genetic evaluation based on cancer type, personal history, family history, and tumor findings.

Important limitation: Genetic testing is not appropriate or necessary for every cancer patient, and recommendations vary by cancer type and individual circumstances.

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