Thyroid cytology report

Your Thyroid FNAC Report: — What Each Bethesda Category Means

A Bethesda category number is not a diagnosis. It is the cytologist's standardised way of telling your team how much malignancy risk the sample carries — and which step is appropriate next.

Medically reviewed by Dr. C. Raghavendra Reddy, Medical Oncologist, MBBS (Gold Medal) · DNB · DM (Medical Oncology, Gold Medal) · Last reviewed September 2026

Six categories, not a verdict — Each number describes what the cytologist saw under the microscope, not whether you have cancer.
Risk ranges, not certainties — Every category carries a published malignancy risk range that applies to large groups of patients, not to your individual case.
Category drives the next step — Your oncologist uses the number to choose between monitoring, repeat biopsy, molecular testing, or surgery.
Benign is the most common result — Category II — Benign — is the most frequent finding across large thyroid FNAC series worldwide.

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The Bethesda System divides thyroid FNAC results into six categories, I to VI. Each carries a published malignancy risk range from the Bethesda System for Reporting Thyroid Cytopathology (BSRTC). Category II is benign; Category VI is malignant. The number on your report tells your team which step to take next.

What is the Bethesda System and why does your thyroid report use it?

The Bethesda System for Reporting Thyroid Cytopathology (BSRTC) is a standardised six-category framework used by cytologists worldwide to report fine needle aspiration cytology of thyroid nodules.

It ensures that a Category III result from a laboratory in Hyderabad means the same thing as a Category III result from a laboratory in Chennai — and that both point to the same management pathway.

The system was updated in 2023. The third edition revised some malignancy risk ranges after a thyroid tumour type called NIFTP was reclassified as non-malignant, which lowered the true cancer rate attributed to several of the middle categories.

What does each category mean?

Category I — Non-diagnostic or Unsatisfactory: The sample did not contain enough representative cells for a reliable reading. This is a technical limitation of the biopsy, not a finding about the nodule itself. The procedure is usually repeated after an interval.
Category II — Benign: The cells look normal. This covers findings such as a colloid nodule, thyroiditis, or benign cyst. It is the most common result and usually leads to monitoring with ultrasound rather than surgery.
Category III — Atypia of Undetermined Significance (AUS): Some cells look mildly abnormal but not clearly suspicious or malignant. This is a genuinely uncertain category. The usual next step is a repeat biopsy after an interval, or molecular testing on the original sample.
Category IV — Follicular Neoplasm: The cell pattern suggests a follicular neoplasm, which may be benign or malignant. FNAC alone cannot tell them apart, because distinguishing the two requires examining how cells invade tissue — which needs a surgical specimen.
Category V — Suspicious for Malignancy: The features strongly suggest malignancy but do not fully meet the criteria for Category VI. Most cases in this group turn out to be malignant when the surgical specimen is examined.
Category VI — Malignant: The cells meet the cytological criteria for a cancer diagnosis, most commonly papillary thyroid carcinoma. Surgery is the standard next step.

What malignancy risk does each category carry?

Category	Name	Malignancy risk range (BSRTC 2023)	Usual next step
I	Non-diagnostic	5–10%	Repeat FNAC after interval
II	Benign	0–3%	Ultrasound follow-up
III	Atypia of Undetermined Significance	13–30%	Repeat biopsy or molecular testing
IV	Follicular Neoplasm	23–34%	Diagnostic lobectomy
V	Suspicious for Malignancy	68–83%	Surgery (usually total thyroidectomy)
VI	Malignant	97–99%	Surgery (usually total thyroidectomy)

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What happens after the result?

Risk figures in the table are population-level ranges from BSRTC third edition (2023). They describe large groups of patients across many centres — not the probability for your specific nodule.

Your oncologist will consider the category alongside the nodule size, ultrasound characteristics, your clinical history, and where relevant, a molecular test result before recommending a plan.

Categories III and IV in particular allow for different approaches depending on the full picture. A result in this range does not automatically mean surgery — your oncologist will explain what the options are for your situation.

Did you know?

More than 60 per cent of thyroid FNACs across large multicentre series are reported as Category II — Benign.

The majority of these patients are safely monitored without surgery, according to management data cited in the Bethesda System for Reporting Thyroid Cytopathology.

Source: Bethesda System for Reporting Thyroid Cytopathology, third edition, 2023

Questions families ask about their thyroid FNAC report

Why did the report give a category number instead of saying 'cancer' or 'not cancer'?

FNAC looks at individual cells, not a whole piece of tissue. Some features that distinguish a benign growth from a malignant one — particularly how cells invade surrounding tissue — can only be seen in a surgical specimen. The Bethesda category translates what the cytologist could see into a level of risk, which then guides whether the additional clarity from surgery is worth the procedure. Categories I, II and VI are relatively clear-cut. Categories III, IV and V are the genuinely uncertain zone where the category helps frame the decision rather than make it.

Can a Category II result be wrong?

A benign result carries a small residual malignancy risk — the BSRTC 2023 figure is 0–3% across large series. This is why ultrasound follow-up matters even with a reassuring report. If a nodule grows on repeat imaging, or new symptoms appear, your team may recommend a repeat biopsy. A single normal result is not a reason to stop monitoring when the clinical picture warrants continued surveillance.

What is NIFTP and why did it change the risk figures?

NIFTP — noninvasive follicular thyroid neoplasm with papillary-like nuclear features — was previously classified as a form of papillary thyroid carcinoma. In 2016 it was reclassified as a non-malignant or low-risk entity, because surgery alone treats it reliably without additional treatment. Reclassifying it lowered the true malignancy rate attributed to several Bethesda categories, which is why the 2023 BSRTC risk ranges for Categories III, IV and V are higher than those in the earlier 2017 edition when NIFTP was excluded from the malignant column. If your report or consultation mentions NIFTP, ask your oncologist what this means for your management plan.

Can a second opinion change my category?

It can. Thyroid cytology has recognised inter-observer variability, particularly for Category III, where distinguishing mild atypia from normal cellular variation involves a degree of expert judgement. A review by a specialist thyroid cytopathologist can be useful when you have an indeterminate result and are weighing a major decision such as surgery. Ask your treating team whether a slide review is available or appropriate in your case before proceeding to an operation on the basis of a single reading.

Is molecular testing available in India for indeterminate thyroid nodules?

Molecular panels — tests that look for specific genetic mutations in the biopsy sample — are available in India, though accessibility and public funding vary by centre. For Category III and IV nodules, a mutation result can shift the clinical decision meaningfully in either direction: towards continued surveillance or towards surgery. Both NCCN guidance and the BSRTC third edition discuss their role in indeterminate nodule management. Ask your oncologist whether molecular testing is appropriate for your nodule size and category, and which panel would be relevant for your specific situation.

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Common questions

Frequently asked questions

What does a Bethesda Category III result mean for my treatment?

Category III — Atypia of Undetermined Significance — is the most uncertain of the six categories, and management varies. Options include repeat biopsy after a short interval, molecular testing on the original sample, or in some cases diagnostic surgery, depending on your nodule's size and ultrasound features. BSRTC 2023 puts the malignancy risk range for this category at 13–30% across large series. Your oncologist will explain which option fits your clinical picture, and it is reasonable to ask why one approach is preferred over the others.

Can I avoid surgery with a Category IV result?

Sometimes, particularly when molecular testing gives a reassuring result. Category IV — Follicular Neoplasm — is indeterminate because FNAC cannot tell a benign follicular adenoma from a follicular carcinoma without examining how the cells invade tissue, which requires a surgical sample. Molecular panels are increasingly used to stratify the risk before operating. Ask your oncologist whether molecular testing is an option for your nodule and what a reassuring result would change in the management plan.

How long does a thyroid FNAC result take?

Most results are available within five to ten working days. Laboratories that process cytology in-house tend to be faster; if the sample needs specialist review or molecular testing, it takes longer. Ask the team at the time of the biopsy when to expect the result and who will contact you. If you have not heard within the expected window, call the clinic rather than waiting — results do not always reach patients automatically.

My report says AUS — is that the same as Category III?

Yes. AUS — Atypia of Undetermined Significance — is the most common label used for Bethesda Category III. Some laboratories use FLUS — Follicular Lesion of Undetermined Significance — for a slightly different cellular pattern within the same category. Both fall under Category III and carry the same management implications. If your report uses either term, the result is indeterminate and a next step such as repeat biopsy or molecular testing is usually recommended.

Does CION offer thyroid FNAC assessment?

CION provides cancer assessment and treatment across 35 or more centres in Telangana and Andhra Pradesh. Thyroid nodule evaluation, including coordination of imaging, is part of the clinical workup available at CION centres. PET-CT and specialist imaging are coordinated with partner imaging centres. CION does not provide CAR-T or cell therapy. To discuss a thyroid FNAC result or arrange an oncology assessment, contact your nearest CION centre directly.

Should I get a second opinion if my result is suspicious?

A second opinion is reasonable for any indeterminate or suspicious result — particularly Category III, IV or V — where the finding significantly influences a surgical decision. Two forms are possible: a slide review by a specialist thyroid cytopathologist who re-examines the cells, or a clinical opinion from another oncologist who reviews the whole picture together — imaging, clinical features and the cytology report. Both are legitimate and your team should be able to facilitate either. You do not need to feel that asking is a challenge to your treating doctor.

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