Medical Oncologist
Monitoring & Results
Are Tumour Markers — Reliable on Targeted Therapy?
A changing tumour marker number is not always a verdict on how your treatment is going. On targeted therapy especially, markers can move in ways that look alarming on paper — and need context before they mean anything.
Medically reviewed by Dr. Bharati Devi Gorantla, Medical Oncologist, MBBS · MD · DM (Adyar, Chennai) · ECMO · MRCP SCE (UK) · Last reviewed August 2026
- Not a standalone number — Your oncologist reads markers alongside scans and symptoms, not in isolation.
- Rises can be misleading — A marker can go up in the first weeks of treatment even when it is working.
- Falls are encouraging, not conclusive — A falling marker is a good sign, but confirmation of response requires imaging.
- Trend matters more than any single reading — One result rarely changes a plan. The pattern over several tests is what guides decisions.
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Tumour markers are not always a reliable guide to how your treatment is working, especially on targeted therapy. They can rise temporarily when treatment starts, fall for reasons unrelated to cancer, and stay elevated even when cancer is responding well. Your oncologist interprets markers alongside scans, not as a standalone verdict.
Why do tumour markers sometimes rise when treatment is working?
When cancer cells die in response to treatment, they release proteins stored inside them. Those proteins enter the bloodstream and briefly raise the marker reading — even though the treatment is doing exactly what it should.
This is called a marker flare. It is most common in the first few weeks after starting a new treatment and can look alarming on a printed result.
Your oncologist will repeat the test rather than act on a single rising number. One reading in the wrong direction is rarely a reason to change course.
Can a falling tumour marker confirm the treatment is working?
A falling marker is an encouraging sign — it suggests the treatment may be reducing cancer activity. But it is not proof on its own.
Markers can fall for reasons unrelated to cancer: inflammation settling after a procedure, normal variation between lab readings, or changes in kidney or liver function. ASCO and ESMO guidance is consistent that marker changes should be confirmed by imaging before a treatment decision is based on them.
When your marker falls and your scan improves, that combination gives your team genuine confidence. Either one alone is a signal worth noting, not a conclusion.
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MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
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MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
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What does each term on your tumour marker report actually mean?
- Tumour marker
- A protein or substance released into the blood that can sometimes reflect cancer activity, measured on a routine blood test. What this means for you: the number on its own tells you very little — what matters is how it is moving and how it compares to your own previous results, not to a population reference range.
- Targeted therapy
- A treatment that blocks a specific molecular pathway cancer cells depend on to grow, rather than attacking all dividing cells the way chemotherapy does. What this means for you: because targeted therapies act differently from chemotherapy, markers may behave differently too — your oncologist will explain what pattern to expect at the start of your treatment.
- Marker flare
- A temporary rise in a tumour marker shortly after starting treatment, caused by cancer cells releasing stored proteins as they die rather than by disease worsening. What this means for you: if your marker rises in the first weeks of a new treatment, your team will likely wait and repeat the test before drawing any conclusion.
- Nadir
- The lowest level your marker reaches after treatment starts — the point at which cancer activity, as reflected in the blood, is at its lowest. What this means for you: your oncologist will note your nadir and use it as a personal reference; a meaningful rise above it is an early signal worth monitoring.
- Progressive disease
- A scan finding that the cancer has grown beyond a defined threshold, established by standardised international criteria. What this means for you: a rising marker does not confirm progressive disease on its own — your oncologist will normally want scan evidence before changing your treatment plan.
- Response
- A scan finding that the cancer has shrunk by a meaningful amount, using criteria defined by international oncology guidelines. What this means for you: a falling marker is encouraging, but formal confirmation of response is made from imaging, not from blood tests alone.
What does it mean when your marker result changes?
My marker went up right after I started treatment. Does that mean it is not working?
Not necessarily. A rise in the first weeks is one of the recognised patterns of a marker flare — cancer cells releasing stored proteins as they die. Your oncologist will repeat the blood test rather than act on a single result. If the marker settles or falls at the next reading, and your scan shows stability or improvement, the early rise is unlikely to change your treatment plan. Reporting it to your team is still the right step, so they can confirm that is what they are seeing.
My marker is falling but my doctor has still ordered a scan. Is something wrong?
A scan after a falling marker is not a sign that something is wrong — it is how response to treatment is properly confirmed. ASCO and ESMO guidance is consistent on this: imaging is the standard way to confirm whether the cancer has actually shrunk, because a blood test cannot tell you where the cancer is or whether new areas have appeared. A scan alongside a good marker trend is reassuring. A scan without the marker would give only half the picture.
My marker is within the normal range. Does that mean the cancer is gone?
A normal marker reading is a good sign, but it does not confirm that cancer is absent. Some cancers produce very little of the marker being measured, even when active. Others can be present at a level that does not raise the marker above the laboratory threshold. A normal reading tells you that measurable cancer activity has fallen below the reference point — not that the disease has been eliminated. Your oncologist will explain what the normal range means specifically for your cancer type.
Is the number itself what matters, or only whether it is going up or down?
The direction of change, and the rate of change, usually matter more than the absolute number. A marker that has fallen significantly from a much higher starting point is a very different picture from one that has recently doubled from a low level. Your oncologist compares each result to your own previous readings rather than to a population reference range. Knowing your personal baseline — what your marker was before treatment started — is what makes each subsequent result interpretable.
What happens if my marker keeps rising despite treatment?
A consistently rising marker on treatment is a signal your oncologist will take seriously. The next step is usually imaging to confirm whether what the marker is suggesting is reflected on a scan — because markers can rise for reasons unrelated to the cancer. If the scan also shows growth, your team will review whether a change in treatment is needed. That decision is made on the combined picture, not on the marker result alone.
Did you know?
Tumour markers can rise from causes that have nothing to do with cancer — including active infection, inflammation, and liver or kidney conditions. This is why ASCO and ESMO guidance consistently recommends interpreting marker results alongside imaging rather than acting on blood test changes in isolation.
Source: ASCO and ESMO guidance on tumour marker interpretation in oncology
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- How to Emotionally Process a Progression Scan
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Common questions
Frequently asked questions
What is the difference between a tumour marker blood test and a biomarker test on my biopsy?
A tumour marker is a blood test measuring a substance circulating in your bloodstream. A biomarker test on a biopsy analyses the genetic or molecular characteristics of the cancer tissue itself. They are different tools with different purposes: biomarker tests on tissue are used to decide which treatment is right for you, while tumour markers in blood are used to monitor how a treatment is going over time. Some tests carry the word biomarker in both contexts, which causes confusion — ask your oncologist which type is being discussed.
How often should my tumour marker be tested while I am on targeted therapy?
The frequency depends on your cancer type, your treatment, and how your results have been behaving. For most patients on active treatment, markers are checked alongside each clinic visit. If results are stable, the interval may lengthen. Your oncologist decides the schedule based on what information the test is adding — more frequent testing is not always more useful, and a stable marker checked very often provides less new information than one checked at the right clinical decision points.
My marker has doubled since last month. Should I be worried?
A doubling is a change worth reporting to your team promptly, but it is not something to interpret alone. The significance depends on where it started, what treatment you are on, whether a scan has been done recently, and how you feel. Contact your oncology team and let them know — they will tell you whether this needs imaging sooner than planned or whether they want to repeat the blood test first. Do not wait until your next scheduled appointment if the change is significant.
Can diet or lifestyle affect my tumour marker result?
For most tumour markers, diet and lifestyle have little direct effect on the number. Inflammation from any cause — an infection, a procedure, or a period of physical stress — can raise some markers. This is one of the reasons a single elevated reading is rarely acted on without context. If you are taking any supplements or have started anything new, let your treating team know, so they can factor it into how they read your results.
Will my tumour marker ever return to normal?
For some patients on effective treatment, markers return to within the normal range and stay there. For others, they fall significantly but remain above the reference range, and that pattern becomes their personal baseline. Whether your marker reaches a population reference value matters less than how it is moving relative to your own starting point. Ask your oncologist what a meaningful response looks like for your specific marker and cancer type — that is a more useful question than whether the number will reach the printed reference.
What should I ask my oncologist when I receive my marker result?
Ask four things: how this result compares to your previous readings, whether it is moving in the expected direction for your treatment, whether a scan is needed to interpret it properly, and what would prompt them to act on the marker rather than simply monitoring it. Writing the answers down helps — these conversations are hard to recall when you are worried. If the result is higher than last time, it is entirely reasonable to ask whether you should be seen sooner or whether a repeat test is planned.