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Lymph node cytology

Sydney System for — Lymph Node Cytology

A lymph node fine-needle aspiration is usually the first tissue test for an enlarged node. The Sydney System gives the report a category number — but that number is not a complete diagnosis, and it comes with an important limitation when lymphoma is suspected.

Medically reviewed by Dr. Mohammed Imaduddin, Surgical Oncologist, MBBS · MS (General Surgery) · M.Ch (Surgical Oncology) · Last reviewed September 2026

  • Five standardised categories — The Sydney System grades FNAC results from SLNC 1 (non-diagnostic) to SLNC 5 (malignant).
  • Lymphoma is the hard case — FNAC can identify malignant lymphoid cells but almost never classifies the lymphoma subtype — which is what treatment depends on.
  • A core biopsy is not a failed FNAC — Being asked for more tissue after a cytology result is standard practice, not a sign that something went wrong.
  • Reactive nodes are the most common result — Most enlarged nodes assessed by FNAC prove benign and reactive, particularly following recent infection.
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The Sydney System for lymph node FNAC uses five categories — SLNC 1 (non-diagnostic) through SLNC 5 (malignant) — to give cytology reports a standardised language. A key limitation: even an SLNC 5 result usually cannot classify lymphoma subtype, which is what treatment planning requires. A core or excision biopsy follows most results above SLNC 2.

What are the five Sydney System categories?

SLNC 1 — Non-diagnostic
The sample did not contain enough lymphoid material to assess. This result does not rule disease in or out. A repeat FNAC or a core biopsy is the usual next step.
SLNC 2 — Benign / Reactive
The node shows reactive or inflammatory changes without features of malignancy. This is the expected result for most nodes enlarged by infection or an immune response.
SLNC 3 — Atypical
Unusual cells are present but cannot be clearly called benign or malignant from the aspirate alone. Further tissue sampling — usually a core biopsy — is generally recommended.
SLNC 4 — Suspicious for malignancy
The cytology pattern strongly suggests a malignant process, but the sample is insufficient to confirm or classify it. Core or excision biopsy is the next step.
SLNC 5 — Malignant
The aspirate contains clearly malignant cells. For metastatic carcinoma this may be sufficient to inform the treatment plan. For lymphoma, FNAC cannot classify subtype — a core or excision biopsy is required before treatment can begin.

When does an FNAC result need a core biopsy?

  • Result is SLNC 1 (non-diagnostic) and a benign cause cannot be safely assumed from the clinical picture.
  • Result is SLNC 3 (atypical) — the sample cannot be classified as benign or malignant on cytology alone.
  • Result is SLNC 4 (suspicious) — confirmation requires tissue architecture that a needle aspirate does not provide.
  • Result is SLNC 5 and lymphoma is the suspected diagnosis — subtype classification always needs a core or excision biopsy.
  • Immunohistochemistry, molecular testing, or receptor status is needed — none of this can be obtained from FNAC material alone.

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How reliable is lymph node FNAC, and where does it fall short?

Lymph node FNAC is reliable for distinguishing reactive nodes from metastatic carcinoma — cancer that has spread from a solid tumour such as breast, lung, or thyroid. For this purpose it performs well and avoids the need for immediate surgical biopsy.

Its main limitation is lymphoma. Classifying most lymphomas requires the internal structure of the node — the pattern in which cells are arranged — alongside immunophenotyping and often molecular analysis. A fine-needle collects individual cells but does not preserve tissue architecture. That is why even a clear SLNC 5 result, when lymphoma is the suspected origin, rarely ends the diagnostic process.

Your team ordering a core biopsy after an FNAC is following standard practice, not repeating a failed test. It reflects an inherent limit of what a needle aspirate can capture, not a technical error.

Did you know?

The WHO Classification of Haematological Tumours (5th edition, 2022) recognises dozens of distinct lymphoma subtypes, each requiring different treatment.

A fine-needle aspirate identifies malignant lymphoid cells — but cannot establish the subtype. That is why a core or excision biopsy follows most SLNC 5 nodal results where lymphoma is the clinical question.

Source: WHO Classification of Haematological Tumours, 5th edition, 2022

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Common questions

Frequently asked questions

What does my SLNC category number mean?

The SLNC category tells your clinical team what the cytologist observed in the sample — it is not a standalone diagnosis. Its meaning depends on your imaging, the behaviour of the node, and your broader clinical history. The category guides whether repeat sampling, a core biopsy, or observation is appropriate. Your oncologist or surgeon interprets it alongside the full clinical picture, and asking them to explain what category was assigned and what the next step is always reasonable.

Does SLNC 2 mean the node is definitely not cancerous?

SLNC 2 indicates that the cells sampled showed reactive or benign changes, but no cytology result carries an absolute guarantee. The result reflects only the cells that were aspirated — different areas of the same node can have different populations. Your team will weigh the cytology result alongside your imaging and the clinical behaviour of the node before concluding that no further investigation is needed.

Why do I need a core biopsy if the FNAC already showed cancer cells?

For metastatic carcinoma — cancer spreading from a solid-tumour primary — an SLNC 5 result can often support a management plan without further sampling. For lymphoma the situation is different. Subtype classification determines whether chemotherapy, targeted therapy, or another approach is used, and that classification requires tissue architecture, immunophenotyping, and often molecular analysis. FNAC captures individual cells but not the structural pattern of the node, so a core or excision biopsy is the necessary next step.

What is the difference between FNAC and a core biopsy?

FNAC uses a thin needle to aspirate individual cells from the node. It takes a few minutes, is usually done with local anaesthetic, and gives information about cell type. A core biopsy uses a wider needle to take a cylindrical tissue sample that preserves the node's internal architecture. That architecture is what pathologists need to classify lymphoma and run immunohistochemistry or molecular testing — which is why a core biopsy follows most nodal FNAC results where lymphoma is the question.

Can FNAC miss cancer in a lymph node?

Yes. Any sampling procedure can miss disease if malignant cells lie in a part of the node that was not aspirated, or if the sample was too small to assess (SLNC 1). This is why your team considers the cytology result alongside imaging and clinical behaviour. A benign or reactive FNAC in a node that remains suspicious on imaging is not the end of the investigation — a repeat sample or a core biopsy is the appropriate next step.

Is the Sydney System used in India?

The Sydney System for Lymph Node Cytology was proposed in 2021 as an international standardised reporting framework. Adoption varies by institution across India and elsewhere. If your report uses different terminology — or no category system at all — the underlying principles are the same: your treating team interprets the result in the full clinical context and advises whether further tissue sampling is needed. Ask your pathologist or oncologist which system was used and what category your result falls into.

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