Biomarkers & Genetic Testing: How Results Guide Cancer Treatment

Cancer treatment is no longer based only on where a tumor started.
Increasingly, decisions are guided by biomarkers—measurable features of a tumor or a person’s DNA that help predict how a cancer behaves and which treatments are most likely to work.

This guide explains:

  • what biomarkers and genetic tests are,
  • the difference between tumor testing and inherited testing,
  • how results influence treatment,
  • and what questions patients should ask.

Important: This is educational information, not medical advice. Biomarker results must be interpreted by your oncology team in clinical context.

60-second orientation

  • Biomarkers are measurable features that give information about a cancer.
  • Some biomarkers come from the tumor itself; others come from a person’s inherited DNA.
  • Biomarker testing can help:
  • select targeted therapies or immunotherapies,
  • avoid treatments unlikely to help,
  • estimate prognosis or recurrence risk.
  • Not all cancers have actionable biomarkers—and that’s normal.

What is a biomarker?

In cancer care, a biomarker is anything measurable that provides information about:

  • how a cancer behaves,
  • how aggressive it may be,
  • or how it might respond to treatment.

Biomarkers can include:

  • proteins on cancer cells,
  • genetic mutations or changes,
  • patterns of gene expression,
  • features of the tumor’s interaction with the immune system.

The most important distinction: tumor testing vs inherited testing

1) Tumor (somatic) testing

This tests the cancer cells, not the rest of your body.

  • Looks for genetic changes that developed in the tumor.
  • Helps identify vulnerabilities that treatments can target.
  • Results apply to the cancer, not your family.

Examples of what tumor testing can influence:

  • eligibility for targeted therapies,
  • likelihood of benefit from immunotherapy,
  • selection of one drug over another.

2) Inherited (germline) genetic testing

This tests the DNA you were born with.

  • Looks for inherited mutations passed through families.
  • Can affect:
  • cancer risk,
  • screening recommendations,
  • treatment decisions in some cancers,
  • family member testing considerations.

Not everyone needs inherited testing—but it can be important in certain situations.

Ask your team:
“Was my testing done on the tumor, my inherited DNA, or both?”

For a cancer-specific overview of commonly tested biomarkers, see

Biomarkers by cancer type →

Common biomarker categories (plain language)

Receptors and proteins

Some cancers depend on specific proteins to grow. Testing can show whether those proteins are present and relevant.

Genetic mutations or alterations

Tumor DNA can contain changes that:

  • drive cancer growth,
  • predict response to certain drugs,
  • or suggest resistance to others.

Not all mutations are actionable—but identifying them can still inform planning.

Immune-related biomarkers

Some tests estimate how likely a tumor is to respond to immunotherapy by evaluating features of immune interaction or DNA repair.

What biomarker results can (and cannot) tell you

What they can do

  • Help match treatment to tumor biology
  • Explain why one therapy is preferred over another
  • Identify clinical trial options
  • Avoid ineffective or unnecessary treatments

What they cannot do

  • Guarantee a treatment will work
  • Replace clinical judgment
  • Predict outcomes with certainty

Biomarkers guide decisions—they don’t make them alone.

Why testing timing matters

Biomarker testing may be done:

  • at diagnosis,
  • after surgery,
  • when cancer recurs,
  • or when considering a new line of therapy.

Results can change over time as cancers evolve under treatment pressure.

Ask:
“Do we need updated testing now, or are prior results still relevant?”

Why results can be confusing for patients

Reports often include:

  • long gene lists,
  • technical terms,
  • variants of unknown significance,
  • findings with no current treatment relevance.

Seeing a mutation listed does not automatically mean:

  • there is a drug for it,
  • it caused your cancer,
  • or it changes your prognosis.

This is why interpretation—not just results—matters.

How VisitVizor helps make biomarker results usable

Biomarker reports are often scattered across:

  • pathology reports,
  • molecular testing PDFs,
  • clinic notes.

VisitVizor helps by:

  • organizing test results alongside your scans and labs,
  • keeping original reports intact,
  • presenting plain-English summaries to support understanding,
  • making it easier to track what was tested, when, and why.

The goal is clarity—not diagnosis—so patients can engage meaningfully with their care team.

Questions patients may want to ask

  • What biomarkers were tested, and why these?
  • Which results actually change treatment decisions?
  • Are there treatments available because of these results?
  • Do any results affect future options or trials?
  • Do I need inherited genetic testing?
  • Should testing be repeated later?

Writing these questions down before visits can help focus discussions.

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