Feline Tumor Fine-Needle Aspiration (FNA) — Procedure, Cost, and Accuracy Guide

Oncology/CancerQ&AMeongsiljang Veterinary Advisory Board

We’ve put together a clear, easy-to-understand guide for pet owners on the fine-needle aspiration (FNA) test—the first step when a tumor is found in a cat. Learn about the procedure, cost range, accuracy, and limitations, as well as what to expect before and after the test, how results are interpreted, and when additional biopsies may be needed.

What Is Feline Tumor Fine-Needle Aspiration (FNA)? One-Line Summary

A veterinarian performing a fine-needle aspiration biopsy on a skin mass located on a cat’s shoulder.

Feline fine-needle aspiration (FNA) is a primary diagnostic test in which a thin needle is used to directly collect cells from a mass for microscopic analysis. The key point is that when a tumor is detected, the first step is not immediate surgery but rather starting with FNA. The procedure typically takes only 5 to 10 minutes and can be performed without sedation or anesthesia, allowing for a rapid assessment of whether the mass is likely benign or malignant. However, because some tumors, such as lymphoma, are diagnosed based on cellular morphology while others are not, a biopsy may be required depending on the FNA results.

When Is Fine-Needle Aspiration Recommended?

Lumps felt on a cat’s body or masses detected via imaging cannot be distinguished as benign or malignant based on appearance alone. A definitive assessment requires direct examination of the cellular morphology. Therefore, fine-needle aspiration (FNA) is recommended as the first step in the following situations: - Palpable lumps: When a subcutaneous mass persists for more than 2–4 weeks or grows rapidly. - Mammary masses: Since the benign or malignant nature of feline mammary masses cannot be determined by appearance alone, it is best to confirm the cellular characteristics via FNA immediately upon discovery. - Lymph node enlargement: When lymph nodes under the jaw, in the armpits, or in the groin are swollen asymmetrically. FNA is particularly useful for evaluating both nodules and lymph nodes. - Abdominal masses: When a mass is palpable or detected on imaging, accompanied by decreased appetite and weight loss. Samples from deep areas such as the spleen or liver are collected under ultrasound guidance. - New nodules found during follow-up visits: Any new nodules that were not present during previous examinations.

Fine-Needle Aspiration vs. Core Biopsy vs. Excisional Biopsy — At a Glance

Item	Fine-needle aspiration (FNA)	Core biopsy	Excisional biopsy
Sample amount	Cell-level (small amount)	Portion of tissue (core)	Entire mass
Anesthesia	Usually no sedation	Sedation or local anesthesia	General anesthesia required
Time required	5–15 minutes	15–30 minutes	30 minutes to several hours
Diagnostic accuracy	About 80–89% depending on reports	Generally higher than fine-needle aspiration	Highest (evaluation of entire mass)
Cost burden	Low	Medium	Highest
Main use	Primary screening	Definitive diagnosis of tumors other than lymphoma	Both treatment and definitive diagnosis

Accuracy varies depending on tumor type, location, and degree of inflammation. Some reports indicate the diagnostic yield of fine-needle aspiration for liver/spleen tumors is as low as 14–33% (Wang et al., 2004).

Procedure — From Sampling to Interpretation

Fine-needle aspiration is typically performed right in the outpatient clinic without sedation. 1. Site disinfection and stabilization: The veterinarian stabilizes the mass by holding it firmly with one hand. 2. Needle insertion: A fine needle (22–25 gauge) is inserted into the site. 3. Cell collection: Cells are obtained using either aspiration (creating negative pressure with a syringe) or non-aspiration (moving the needle back and forth multiple times). 4. Imaging guidance: For deeper structures such as the spleen or liver, ultrasound guidance ensures precise needle placement. 5. Smear preparation and staining: The sample is spread onto a slide and stained with Diff-Quik or Wright stain. 6. Interpretation: A veterinary pathologist analyzes the sample under a microscope, with results usually available within 3 to 7 days.

A veterinarian's hands performing an ultrasound-guided fine-needle aspiration of a cat's abdominal organs

Key Pre-Procedure Checks

Fine-needle aspiration is a relatively safe procedure, but cats with bleeding tendencies or low platelet counts are at risk of post-procedural bleeding or hematoma. To ensure safety, basic blood tests and coagulation times (BMBT or PT/aPTT) should be checked before the procedure. Additionally, because intrathoracic masses carry a risk of pneumothorax and splenic masses may cause intra-abdominal hemorrhage, cats should be monitored for 30 to 60 minutes after the procedure. For pregnant cats or those in a state of extreme agitation, it is safer to perform the procedure after sedation.

Feline Tumor Testing Costs — Ranges by Site and Guidance

The cost of feline tumor testing varies depending on the sampling site and whether imaging guidance is used. Below is a general price range at typical veterinary clinics (as of January 2026). - Superficial masses (skin, superficial lymph nodes): Procedure fee $40 to $70 - Ultrasound-guided abdominal organs (spleen, liver, kidneys): Procedure fee $70 to $100 - CT-guided thoracic or deep masses: Procedure fee $100 to $300 - Pathology interpretation fee: $40 to $90 additional, depending on the site and number of slides If sedation or anesthesia is required, an additional $40 to $100 will be charged. For an accurate estimate, please contact your veterinary clinic directly before the procedure.

A veterinarian explaining tumor testing costs to a cat owner at the animal hospital.

Accuracy and Limitations — When Additional Testing Is Needed

The accuracy of fine-needle aspiration (FNA) varies significantly depending on the tumor type, location, and degree of inflammation. While the overall reported sensitivity of cytology is approximately 89% and specificity is 100%, there are notable differences among tumor types. - Lymphoma: As a round-cell tumor, it is highly suitable for FNA cytology, making this method useful for diagnosis. - Mast cell tumor: Relatively easy to identify via FNA, but histopathology is required for grading. - Mammary tumors and soft tissue sarcomas: Limitations in sample collection and interpretation can make it difficult to distinguish between benign and malignant lesions. - Liver and spleen tumors: Diagnostic yield is low (14–33%; 14% in dogs, 33% in cats; Wang et al., 2004) because cells do not exfoliate well and samples are often contaminated with blood. If results are reported as "non-specific" or "insufficient for diagnosis," a definitive diagnosis requires core needle biopsy or excisional biopsy. In particular, for mast cell tumors, histopathology is essential for determining grade and prognosis, even if the tumor is identified via FNA.

Notes on Interpreting Results

Even if a fine-needle aspiration report reads "negative" or "inflammatory changes," it cannot rule out a tumor with 100% certainty. This is because normal tissue may be present within the mass, or the sampled area may not represent the center of the tumor. Therefore, if clinical suspicion for a tumor remains high despite ambiguous results, a follow-up test should be performed in 2–4 weeks, or a core needle biopsy or excisional biopsy should be conducted. Please note that the phrase "consistent with" on the report does not indicate a definitive diagnosis, but rather suggests a high likelihood.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

Doesn't my cat hurt a lot during the examination?

The needles used are thinner than those for vaccinations (22–25 gauge), so the discomfort is brief and mild. The procedure usually takes only 5–10 seconds, and most cats tolerate it well without sedation. However, sensitive cats or those requiring sampling from deeper sites may need light sedation.

What should I do if the test result comes back as “nonspecific”?

This occurs when insufficient cells are collected or when tumor cells do not transfer well to the slide. We recommend retesting in 2–4 weeks, or if clinical suspicion remains, confirming the diagnosis with a needle biopsy or excisional biopsy. Rather than interpreting this result as simply

Does a needle aspiration cause the tumor to grow faster or spread?

According to veterinary surgery textbooks and numerous studies, there is no clear evidence that fine-needle aspiration causes tumor spread or accelerates growth. Although very rare cases of needle-track seeding have been reported with core biopsies, the risk is negligible with fine-needle aspiration because the needle is much thinner. Delaying the test is actually more dangerous, as it can cause you to miss the optimal window for diagnosis and treatment.

Does a negative result mean I can be completely reassured?

Not necessarily. Fine-needle aspiration may yield a false-negative result if the sample isn’t taken from the center of the tumor. If clinical signs persist or the mass continues to grow, further testing—including a repeat aspiration or a biopsy—should be performed even if the initial result is negative.

How long does it take to get the results?

In-house diagnostics can be completed on the same day or by the next day, while detailed analysis by an external veterinary pathologist typically takes 3 to 7 days. In urgent cases, we can provide a preliminary rapid assessment first, with the comprehensive results to follow.

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References

[1] Raskin RE, Meyer DJ. Canine and Feline Cytology: A Color Atlas and Interpretation Guide, 3rd Edition. Elsevier, 2016

[2] Valenciano AC, Cowell RL. Small Animal Cytologic Diagnosis: Canine and Feline Disease, 2nd Edition

[3] Kudnig ST, Séguin B. Veterinary Surgical Oncology, 2nd Edition. Wiley-Blackwell

[4] Wang KY et al., Accuracy of ultrasound-guided fine-needle aspiration of the liver and cytologic findings in dogs and cats: 97 cases (1990-2000). JAVMA, 2004

[5] Jasik A et al., BSAVA Manual of Canine and Feline Dermatology, 4th Edition (Chapter 34: Neoplastic and paraneoplastic syndromes affecting the skin)