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Molecular & Genomic Testing

Can Molecular Testing Be Done — on an Old Block?

Paraffin-embedded tissue blocks stored in a hospital's pathology department can often still be used for molecular testing years later. The DNA inside degrades slowly, and many blocks from five to ten years ago — or older — still yield a usable result.

Medically reviewed by Dr. Muralidhar Muddusetty, Surgical Oncologist, MBBS (AIIMS) · MS Surgery (AIIMS) · DNB Surg Onc · MRCS (Edinburgh) · Last reviewed September 2026

  • Old blocks often work — Many archived blocks contain enough DNA for molecular testing, even years after the original procedure.
  • No repeat procedure needed — A usable archived block means you may not need another biopsy to get tissue for testing.
  • Quality is checked first — The laboratory assesses DNA before testing begins, so you know early if the sample is usable.
  • Storage matters as much as age — How the block was kept affects DNA quality as much as how many years have passed.
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Molecular testing can often be done on paraffin-embedded tissue blocks stored for years. DNA does degrade over time, but many archived blocks — even from five to ten years earlier — still yield enough material for testing. Your oncologist requests retrieval; the laboratory assesses DNA quality before testing begins.

What do the terms on a molecular testing request mean?

Paraffin block (FFPE block)
Your tumour tissue, preserved in formalin and embedded in wax after your biopsy or surgery. It is stored at room temperature and is the standard archive in pathology departments across India.
FFPE
Formalin-fixed, paraffin-embedded. The preservation method used in virtually every pathology department in India and worldwide, which is why archived blocks are compatible with modern molecular testing.
Archived block
A block stored in a hospital's pathology department after your original procedure. Most hospitals keep blocks for a defined period — often ten years or more — as a routine part of record-keeping.
DNA extraction
The step where the laboratory separates genetic material from the preserved tissue. The quality of that DNA — not just whether it is present — determines whether a reliable result is possible.
Tumour content
The proportion of cancer cells in the section cut from the block. A sample with too few tumour cells may not yield a usable result, regardless of how well-stored the block is.
Molecular panel / NGS
Next-generation sequencing or a targeted gene panel — the tests that identify mutations in your tumour. They require a minimum amount of good-quality DNA to produce a reliable answer.

What do I need to do to get my archived block tested?

  • Ask your oncologist to write a formal retrieval request — pathology departments release blocks on a clinical request from a treating doctor.
  • Identify which hospital holds the original block and confirm the department that archived it.
  • Check that the block is from the same tumour site your oncologist needs information about.
  • Keep a copy of the original pathology report — it confirms the block's identity and speeds up retrieval.
  • Allow one to two weeks for retrieval and DNA quality assessment before testing begins.
  • Ask the laboratory whether the block will be returned after testing, or whether part of it will be consumed.

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How old is too old for molecular testing?

There is no fixed age limit beyond which a block cannot be tested. Many laboratories successfully extract usable DNA from blocks that are ten years old or older.

What matters most is how the block was stored. A block kept at a stable, dry room temperature in a sealed container degrades more slowly than one exposed to humidity or temperature fluctuations over the years.

The laboratory will assess DNA quality before committing to the test and will tell your oncologist if the sample is unlikely to yield a reliable result. A repeat biopsy is the fallback — but most archived blocks from the last decade are worth attempting first.

What should I know before sending my block for testing?

Does the testing use up the whole block?

No. The laboratory cuts thin sections from the block for DNA extraction — not the entire block. How many sections are needed depends on the test and the tumour content of the sample. In most cases the bulk of the block remains and can be returned to the originating pathology department. Ask the laboratory about their specific policy before the block is sent.

What if the hospital cannot find my block?

Ask the pathology department to search their archive using your name, procedure date, and hospital registration number — blocks are indexed records, not loose items. If the block cannot be located, ask whether any unstained slides from the original biopsy are available, as these can sometimes substitute. If neither is retrievable, your oncologist will advise whether a fresh biopsy is clinically appropriate for your situation.

Can a blood test be used instead of the block?

Liquid biopsy — testing tumour DNA circulating in the blood — is available for some cancer types and specific markers. It does not replace a tissue block test for every situation, but it can answer certain questions without a new procedure. Whether it is appropriate for your case depends on your cancer type and the markers being tested. Ask your oncologist before arranging block retrieval whether liquid biopsy is an option.

Will results from an old block still apply to my current disease?

Molecular results from an archived block describe the tumour as it was at the time of that biopsy. Tumours can change their characteristics over time — particularly after treatment — so results from many years ago may not fully represent your current disease. Your oncologist will weigh the time elapsed and your treatment history when deciding whether the archived block is sufficient or whether a fresh sample is preferable.

What if the block is held at a hospital in another city?

Blocks are routinely transported between cities and sent to specialist testing laboratories across India. The originating pathology department will know how to package the block securely for courier transit. Allow additional time for transport on top of the retrieval and assessment period. Your oncologist or the testing laboratory can advise on the logistics, and some laboratories will coordinate retrieval directly if given written authorisation.

Is there a cost for retrieval and quality assessment?

Retrieval from the same hospital system is often handled as a standard pathology service, though policies vary and a fee may apply. DNA quality assessment is typically part of the testing laboratory's process. Molecular testing itself is a separate cost, and indicative figures have changed in recent years — ask for a written estimate before the block is sent. Costs vary between laboratories and depend on the panel ordered by your oncologist.

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Common questions

Frequently asked questions

How do I find out where my old block is stored?

Your original biopsy report, surgical report, or discharge summary will name the hospital where the procedure was done. Contact that hospital's pathology department with your name, procedure date, and hospital registration number. Most departments keep indexed records and can locate archived blocks within a few days of a formal request. If you are unsure which hospital holds it, your current oncologist can help trace it.

Will the laboratory tell me if the block is unusable before charging for the test?

Most accredited molecular testing laboratories assess DNA quality before proceeding and will inform your oncologist if the sample is insufficient. Ask the laboratory to confirm this process before the block is sent, and ask what happens to the block if quality is inadequate. If the testing cost is significant, get that confirmation in writing before the block leaves the originating department.

Can I send the block to a laboratory myself, without going through my doctor?

The request should go through your treating oncologist. Your oncologist specifies which test to run, interprets the result in the context of your treatment, and takes clinical responsibility for what follows. A laboratory receiving a block without a clinical request may decline to process it — and a result returned without clinical guidance is not useful to act on alone.

My block is from a lymph node biopsy, not the primary tumour. Does that matter?

It can. Results from a lymph node metastasis may differ from results at the primary site, and some tests are validated specifically on primary tissue. Your oncologist will advise whether the archived site is appropriate for the question being asked, or whether a different sample would give more informative results. Do not assume any old block will answer the current clinical question without checking first.

How long does the whole process take, from retrieval to result?

Allow two to four weeks from when the retrieval request is made to when results are available, though this varies. Retrieval and transit typically take one to two weeks. Quality assessment adds a few days, and molecular testing itself takes one to two weeks once the laboratory accepts the sample. Ask your oncologist for a realistic timeline specific to the test being ordered, so you are not waiting without an expected date.

Is molecular testing on an archived block arranged through CION?

Yes. CION coordinates molecular testing as part of cancer care across its centres, and your oncologist will advise which test is appropriate and arrange the process. If your block is held at another hospital, retrieval is coordinated as part of the workup. The treating oncologist is the right person to initiate this, as the test ordered depends on your specific cancer type and the treatment decision being made.

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