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Biopsy accuracy

Which Cancers Are — Hardest to Diagnose on Biopsy?

Some cancers are genuinely harder to diagnose on a biopsy than others — not because anything has gone wrong, but because of how those cells look under the microscope. Lymphoma, soft-tissue sarcoma, follicular thyroid, and certain liver lesions all fall into this category. Knowing why helps you make sense of a result that took longer than expected, or that needed more than one round of testing.

Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026

  • Some cancer cells look almost normal — Well-differentiated liver lesions and follicular thyroid carcinoma can look nearly identical to healthy tissue, especially in a small sample.
  • Lymphoma has many subtypes — Different lymphoma subtypes look similar on routine staining but require completely different treatment, so the pathologist needs more than the first test to call it correctly.
  • Extra tests increase confidence — Immunohistochemistry and molecular testing are ordered to resolve ambiguity — not because the first reading was wrong, but to make the final diagnosis more certain.
  • A second opinion is always reasonable — Specialist pathology review for difficult cases is standard practice, not an unusual request.
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Some cancers are genuinely harder to read on a biopsy slide than others. Lymphoma, soft-tissue sarcoma, follicular thyroid carcinoma, and well-differentiated liver lesions are among the most challenging. Cells can look almost normal, or indistinguishable from benign tissue. Pathologists use additional stains and molecular tests to reach a confident result.

Why do some biopsies take longer to come back?

A routine biopsy involves staining a thin slice of tissue so a pathologist can study the cells under a microscope. Most cancers have features that make them clearly recognisable this way.

A few do not. Some tumour cells look deceptively normal, or very similar to cells from a completely different type of cancer. When that happens, the pathologist orders additional tests before signing off on a diagnosis.

A result that takes longer, or one that goes to a specialist centre for review, is not a sign that something has gone wrong. It is how the system is designed to catch exactly these cases.

Which cancers are most often difficult to identify on a biopsy?

Lymphoma is one of the most diagnostically demanding cancers. There are many subtypes, several of which look similar under routine staining but require completely different treatment. Identifying it as lymphoma is only the first step — subtyping it correctly is equally important.

Soft-tissue sarcomas are rare, and rare tumours are harder to read. A sarcoma can closely resemble other soft-tissue masses, and some subtypes overlap with each other in appearance, making molecular confirmation important.

Follicular thyroid carcinoma cannot be reliably distinguished from a benign follicular adenoma on a fine-needle aspiration biopsy alone. The difference is often visible only when the entire nodule is surgically removed and examined for signs of capsule invasion.

Well-differentiated liver lesions — including some forms of hepatocellular carcinoma — can look almost identical to normal liver tissue, particularly in small samples taken by needle biopsy.

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What does the pathologist do when the result is not clear-cut?

  1. Routine staining

    Every biopsy is stained with haematoxylin and eosin (H&E) and read under a microscope. Most diagnoses are made at this stage.

  2. Immunohistochemistry (IHC)

    If H&E staining leaves the picture ambiguous, the pathologist adds chemical markers that bind to proteins specific to certain cancer types. This step is standard practice for lymphoma and soft-tissue tumours.

  3. Molecular and genetic testing

    Certain cancers — particularly lymphomas and sarcomas — carry characteristic gene rearrangements. A molecular test can confirm or rule out the diagnosis when cell appearance alone is not enough.

  4. Specialist second opinion

    Difficult cases are routinely sent to a tertiary centre or a pathologist who specialises in that tumour type. This is standard practice, not a signal that the original reading was wrong.

  5. Multidisciplinary team review

    Before treatment begins, oncologists, radiologists and pathologists review all results together. This is a final check that the clinical picture and the pathology are consistent with each other.

What should you do if you are not confident in your result?

It is reasonable to feel uncertain, especially when a result took longer than expected or needed extra tests along the way.

Ask your oncologist to explain what the pathologist found, what additional tests were done, and how confident the final result is. A clear explanation is something you are entitled to expect.

If you remain concerned, a second pathology opinion is standard practice in oncology and your treating team can arrange one. Your treating doctor is the right person to guide you on whether it is warranted for your specific situation — and a persistent concern is always worth raising with them directly.

Did you know?

For lymphoma and soft-tissue sarcomas, specialist pathology review at a second expert centre changes or refines the diagnosis in a meaningful proportion of referred cases.

This is one reason oncology centres routinely send diagnostically difficult slides to a second reader before committing to a treatment plan.

Source: ASCO guidance on pathology quality and specialist tumour review

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Common questions

Frequently asked questions

Does a biopsy that needed extra tests mean my result is less reliable?

Extra tests are ordered to make the result more reliable, not less. A pathologist who orders immunohistochemistry or molecular testing has identified an ambiguity and is resolving it systematically. A diagnosis reached after additional testing is generally better supported than one made from the first stain alone. The extra time is the extra work being done to get the answer right.

What is immunohistochemistry and why does it help?

Immunohistochemistry — often shortened to IHC — uses chemical markers that bind to specific proteins found in certain cancer types. Different cancers produce different proteins, so the pattern of binding helps the pathologist narrow down what the cells are. It is particularly important for lymphoma, where the subtype determines treatment, and for soft-tissue tumours where appearance alone is often not enough to tell subtypes apart.

Should I ask for a second opinion on my biopsy result?

A second opinion is always reasonable for a cancer diagnosis. For certain tumour types — particularly lymphoma, soft-tissue sarcoma and other rare cancers — specialist pathology review is specifically recognised in oncology guidance, including from ASCO, as part of thorough care. Your treating team can arrange this and should not take it as a criticism. Ask your oncologist whether your diagnosis is the kind that commonly benefits from specialist review.

Can a biopsy miss lymphoma even if the sample looked adequate?

It is possible. If the tissue sampled does not contain the abnormal cells, or if the sample is too small for full analysis, the result may not reflect what is happening in the wider lymph node or tissue. If your symptoms continue to suggest lymphoma after a negative or inconclusive result, your oncologist may recommend a repeat biopsy, a larger sample, or a biopsy from a different site. Raise it with your treating team rather than waiting.

Why cannot a needle biopsy of the thyroid tell me whether it is cancer?

A fine-needle aspiration removes individual cells but not the surrounding tissue architecture. For follicular thyroid lesions, the difference between cancer and a benign adenoma is visible only when the pathologist can see whether cells have broken through the nodule's outer capsule — and that requires the whole nodule. If your aspiration result is indeterminate, surgery to remove the nodule is often the only path to a definitive answer. That is the standard clinical pathway for this situation, not a sign that the initial test failed.

How long should a difficult biopsy take to come back?

There is no single timeline that applies to all difficult biopsies. Routine results typically take one to two weeks. When immunohistochemistry or molecular testing is needed, the same sample may take longer. Cases sent to a specialist centre can take longer again. If you are waiting beyond what your team indicated, ask them for an update — they can often follow up with the laboratory. A longer wait more often means more thorough testing is in progress than it means a worse result.

Full index

Browse all 701 biopsy topics

Every page in this section, grouped by the part of the journey it belongs to. Pick a group to see what is in it.

What Is a Biopsy?

What Is a Biopsy? Everything You Need to Know →

Types of Biopsy Compared

Which Biopsy Will You Have? Techniques Compared →

Preparing for a Biopsy

What to Expect on the Day of Your Biopsy →

Recovery and Aftercare

After a Biopsy: Recovery, Aftercare and Warning Signs →

Biopsy by Body Part

Biopsy by Body Part: What to Expect at Each Site →

Understanding Your Report

How to Read a Biopsy Report: Terms Explained →

IHC and Molecular Markers

IHC and Molecular Markers on a Biopsy: What They Mean →

Grading and Scoring Systems

Cytology & Prostate Scoring Systems Explained →

How Accurate Is a Biopsy?

How Accurate Is a Biopsy? Errors and Second Opinions →

If Your Result Is Benign

Your Biopsy Is Benign: What It Means and What Comes Next →

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