Circulating tumour DNA (ctDNA) for monitoring response — what it shows, what it costs, and when it's worth it

ctDNA stands for circulating tumour DNA. It is the small fragments of DNA that cancer cells shed into the bloodstream. A liquid biopsy is a blood test that looks for those fragments and reports whether tumour DNA was found, and at what level. It is a chemical signal in blood, not a picture of the tumour.

Because it is a signal and not an image, ctDNA cannot show where a tumour sits or how large it is. A scan does that. What it can do is measure a quantity that may fall when treatment is working — which is why it is studied so heavily as a monitoring tool.

This page explains the terminology in general. It does not, and cannot, interpret your own report. Whether a particular number matters is a judgement your treating oncologist makes using your full clinical picture.

One thing the marketing tends to leave out: ctDNA is an emerging tool, not a settled part of routine care in India. Outside clinical trials it does not replace your response-assessment imaging. It sits alongside it.

How VAF bands are usually described

Laboratories group VAF into broad bands when they summarise a result. Below is the language you are likely to see. The exact cut-offs are set by each laboratory and each assay — they are not a national standard, and a figure from one lab is not comparable with one from another.

These bands are reporting conventions, not diagnostic thresholds. A single value means little on its own — what oncologists look at is the direction of change across repeated samples from the same assay.

Yes. Several NABL-accredited laboratories in India offer liquid biopsy and ctDNA panels. Blood is usually drawn locally into a stabilising tube and couriered to a central reference laboratory. Some comprehensive genomic-profiling panels are still processed abroad, which lengthens turnaround.

Turnaround — commonly around one to three weeks, depending on panel size and whether the sample travels overseas. Ask for it in writing first: a result that arrives after the next treatment decision has cost money and gained nothing.

Available is not the same as indicated. Most patients in India on checkpoint inhibitor immunotherapy are monitored with imaging, blood tests and clinical review, as guideline bodies such as NCCN, ASCO and ESMO describe. ctDNA is ordered selectively, for a specific question.

Immunotherapy is administered as day care at CION centres. Response-assessment PET-CT is coordinated at partner imaging centres, not performed in-house, and molecular tests including ctDNA panels are sent to accredited external laboratories.

Indicative only, as of August 2026. Insurance cover for liquid biopsy in India is inconsistent and often declined as investigational — check your policy wording, and Aarogyasri, CGHS, ECHS or ESI entitlements where they apply. The most-missed cost is repetition: one test rarely answers a monitoring question.

It is worth the cost only if the result would change a decision. That is the whole test. If your oncologist already has a clear plan from your imaging and your clinical picture, an expensive result that confirms what everyone believed has bought reassurance, not care — worth naming as such rather than dressing up as monitoring.

This matters here more than elsewhere because ctDNA is marketed hard. It is promising science and it is commercial. Both are true. The useful question is not “is this advanced?” but “what would we do differently depending on the answer?”

Where it may add something

• Tissue is unavailable or exhausted. Where a repeat biopsy is not safe or possible, a blood panel may be the only route to genomic information.
• A specific, actionable question exists. Hunting a known variant with an approved treatment attached is different from broad curiosity.
• You are in, or being considered for, a clinical trial. Trials often build ctDNA into the protocol, so it is part of the study rather than an out-of-pocket extra.
• Your team says the result would change the plan. Ask them to say exactly how. A clear answer is a good sign; a vague one is informative too.

Where it usually does not

• As a substitute for a scheduled scan. Outside trials, ctDNA is not an accepted replacement for response-assessment imaging.
• As a one-off reassurance test. A single value says little; the information is in the trend across repeated samples.
• To settle an ambiguous scan on its own. The standard step remains a confirmation scan four to eight weeks later.
• When the plan will not change either way. If treatment continues regardless of the number, the number costs money and worry.

If you are funding a relative's treatment from abroad, hold on to this section. Being asked to approve a test whose report you will never see is stressful, and the pressure to say yes to anything described as advanced is real. Ask the treating oncologist one question in writing: what would we do differently depending on the result? If there is no clear answer, the test can usually wait.

Not on its own, and not in a way that currently replaces imaging. Research reported through bodies such as ASCO and ESMO has examined whether an early fall in ctDNA tracks with later response on scans, and in some cancer types the direction of travel is encouraging. Assays, thresholds and timing are not standardised, so it adds to the picture rather than standing in for it.

The two measure different things. A scan measures size and location at one moment. A ctDNA level measures how much tumour DNA was circulating when the blood was drawn. They can move in different directions, and that mismatch is unsettling to read without context.

The pseudoprogression question. The most-discussed hope for ctDNA is telling apparent growth apart from real growth: if the scan looks bigger while ctDNA is falling, the growth may reflect immune activity rather than the cancer expanding. Early work is promising, but the evidence is not yet mature enough for routine use in India. The standard response to an ambiguous scan remains a confirmation scan four to eight weeks later, with response-assessment PET-CT coordinated at partner imaging centres.

Guideline bodies are explicit that immunotherapy response assessment rests on imaging, clinical assessment and standard blood work. Saying plainly that the ctDNA evidence is still maturing is not scepticism — it is the difference between a test that informs your care and one that decorates it.

• Pseudoprogression: When the Tumour Looks Bigger but Treatment Is Working — the phenomenon ctDNA is being studied to help resolve, explained in full.
• Immune-Related Findings on a Scan That Are Not Cancer — why immunotherapy can put things on a scan report that alarm you and are not the cancer.
• Why Two Radiologists Read the Same Scan Differently — useful context on how much variation is normal before you buy an extra test to settle it.
• Immunotherapy at CION Cancer Clinics — how immunotherapy is delivered as day care, and how monitoring is coordinated.

This page explains general terminology for patient education and does not interpret any individual test or scan report. Cost figures are indicative third-party laboratory pricing as of August 2026, not a CION rate card or a quotation. Clinical framing follows patient-education guidance from bodies including NCCN, ASCO and ESMO; ctDNA monitoring is an evolving area and practice may change. Response-assessment PET-CT referenced here is coordinated at partner imaging centres.

Families ask us this before spending on a new test

Reading the research yourself and wanting the numbers to make sense is not overthinking it. Our team will tell you plainly when a test is worth arranging — and when it is not.