Cytology reporting

Breast FNAC Categories: — The Yokohama System

A number on your breast FNAC report describes how confident the cytologist is about the result — not whether you have cancer. For most treatment decisions, a core biopsy will still be needed.

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

Five categories, not five diagnoses — Each reflects how certain the result is, from too few cells collected to cytology consistent with malignancy.
Core biopsy usually follows — A tissue sample is needed before surgery or systemic treatment can be planned for any solid lump.
Atypical does not mean likely cancer — Category 3 is inconclusive — the cells need a better sample to interpret, not a partial verdict.
FNAC cannot test receptors — Hormone receptors and HER2, which drive most treatment decisions, can only be measured from tissue.

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The Yokohama System divides a breast FNAC report into five categories, from Unsatisfactory to Malignant, each reflecting how confident the cytologist is about the result. The category is not a diagnosis. For most treatment decisions, a core biopsy is needed after FNAC — it is the only way to test hormone receptors and HER2.

How does breast FNAC compare to a core biopsy?

	Breast FNAC	Core needle biopsy
What the needle collects	Individual cells (cytology)	A small tissue core (histology)
Hormone receptor testing (ER/PR)	Not possible	Standard — part of every result
HER2 testing	Not possible	Standard — part of every result
Sufficient for treatment planning	Usually not on its own	Usually yes
Anaesthetic or stitches needed	Neither	Local anaesthetic; no stitches
Preferred for	Axillary nodes, cysts, rapid assessment	Primary solid breast lump

Why has core biopsy largely replaced FNAC for breast lumps?

Breast cancer treatment is guided by hormone receptor status (ER and PR) and HER2 status. These markers determine whether hormone therapy, targeted treatment, or chemotherapy is recommended. FNAC collects loose cells; measuring these markers requires intact tissue architecture, which only a core biopsy provides.

FNAC is still the right tool for assessing axillary lymph nodes, draining cysts, and rapid on-site review. For a primary solid lump where treatment planning is the goal, core biopsy is now the standard first test, in line with NCCN and ESMO guidance.

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What does each Yokohama category mean?

Category 1 — Unsatisfactory: Not enough cells were collected to make a reliable assessment. This does not indicate benign or malignant — the test needs to be repeated or a core biopsy done instead.
Category 2 — Benign: The cells look non-cancerous. The probability of malignancy is low, per International Academy of Cytology data. Even a benign result may be followed by core biopsy if imaging or clinical findings point differently.
Category 3 — Atypical: Cells show unusual features that do not read clearly as benign or malignant. This is an inconclusive result, not a partial verdict of cancer. Core biopsy is the standard next step. Most people with Category 3 do not have cancer.
Category 4 — Suspicious of malignancy: Cells strongly suggest malignancy but fall just short of the criteria for a definitive cytological diagnosis. Core biopsy is needed before any treatment decision is made.
Category 5 — Malignant: Cytology is consistent with cancer. Core biopsy is still done before treatment to confirm tissue type, grade, and receptor status — all of which determine the actual plan.

When will your team move to a core biopsy?

The lump is solid on ultrasound or mammogram
The FNAC result is Category 3, 4, or 5
Hormone receptor or HER2 status is needed for treatment planning
The FNAC was Category 1 — not enough cells were collected
Surgery is being planned and a confirmed tissue diagnosis is required first
Imaging and FNAC results point in different directions

Questions about your Yokohama report

My report says Category 3 — atypical. Does that mean cancer is likely?

Category 3 is inconclusive, not alarming. The cells have features that do not fit clearly into the benign or malignant groups. The malignancy risk for Category 3 spans a wide range across different patient groups and centres — which is exactly why core biopsy, not watchful waiting, is the standard recommendation. Most people who have a core biopsy after a Category 3 result do not have cancer. The word 'atypical' describes what the cytologist saw under the microscope, not the clinical situation you are in.

Can the FNAC result be wrong?

Yes. The most common error is a false-negative — a benign result when cancer is present — and it usually happens when the needle did not collect cells from the right part of the lump. This is one of the main reasons FNAC is no longer used alone for solid lump assessment. Clinical management combines the FNAC result with imaging and examination. If any two of those three disagree, the suspicious finding leads and a core biopsy follows. Core biopsy significantly reduces the false-negative rate by sampling a tissue core rather than loose cells.

Why can FNAC not test hormone receptors?

Hormone receptor testing (ER and PR) and HER2 testing use methods validated for intact tissue sections, not isolated cells. A fine needle aspirate removes cells from their structural context, and that context matters for accurate interpretation. ASCO and ESMO both require tissue-based results — from a core biopsy — before hormone therapy or HER2-targeted treatment is prescribed. A core biopsy is the only way to obtain that information before treatment starts.

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Common questions

Frequently asked questions

What does a Category 3 result mean for my next steps?

Category 3 means the FNAC is inconclusive — the cells are unusual but not clearly benign or malignant. Your team will recommend a core biopsy, which takes a tissue core rather than loose cells and is more likely to give a definitive answer. Most people who go on to have a core biopsy after a Category 3 result do not have cancer. The category points to what happens next, not to a likely diagnosis.

Can the FNAC result be wrong?

Yes, and this is one of the main reasons FNAC is no longer used as a standalone test for solid breast lumps. The most common error is a false-negative — a benign result when cancer is present — usually because the needle did not reach the right area. Your team combines the FNAC result with imaging and examination findings. If any of those three disagree, a core biopsy follows regardless of the FNAC category.

My result says Category 5 malignant. Does that mean I definitely have cancer?

Category 5 means the cells seen are consistent with malignancy — a strong indicator, not a confirmed final diagnosis. Confirmation comes from the core biopsy, which also provides the hormone receptor and HER2 status essential for treatment planning. Your oncologist will not plan surgery or systemic treatment on an FNAC alone. A Category 5 result means the next steps move quickly, not that decisions have already been made.

Is FNAC still used in Indian hospitals, or has core biopsy replaced it?

FNAC is still widely used in India for axillary lymph node assessment, cyst drainage, and rapid on-site review. For primary solid breast lump diagnosis in centres with full equipment, core needle biopsy has become the preferred first-line test, in line with NCCN and ESMO guidance. Both tests have a role — the choice depends on the clinical question being asked, not on one being universally superior.

How long does a core biopsy take, and is it painful?

A core needle biopsy is done under local anaesthetic, usually with ultrasound guidance, and takes around 20 to 30 minutes in total. Most people feel pressure rather than pain during the procedure. There is often bruising and tenderness for a few days afterwards, and no stitches are needed. Results typically take one to two weeks depending on the tests requested on the tissue.

What is the difference between FNAC, core biopsy, and surgical biopsy?

FNAC uses a thin needle to aspirate loose cells. A core biopsy uses a slightly wider needle to remove a small tissue core under local anaesthetic, without stitches or an operating theatre. A surgical biopsy removes a larger piece of tissue or the whole lump under general or regional anaesthesia. For most breast lumps, a core biopsy gives the diagnostic information needed. Surgical biopsy is now rarely done for diagnosis alone — it is reserved for lumps a needle cannot safely reach.

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