fna results for skin lumps

I am looking for data on the diagnostic accuracy of fine needle aspiration (FNA) compared to surgical biopsy for subcutaneous masses in cats.

I have seen conflicting information online. Some sources state FNA is 90% accurate, while others suggest it can miss low-grade sarcomas. I have a 9-year-old tortie, Vera, who has arthritis, so I want to avoid unnecessary surgery if possible, but I need to know the reliability of the non-invasive option.

Has anyone here had a mass diagnosed via FNA that was later found to be different upon excision? I am trying to calculate the risk-benefit ratio.

i had this happen with my gray shorthair Olive. she had a lump that looked hard. the vet did an fna and said it was a lipoma. we were happy. but then it kept growing. we ended up having to take it out a few months later. it was actually a different type of tumor. so yeah fna can be wrong. i posted about it here Olive's weird skin bump if you want to see the pics.

I am not a fan of the fancy terms but I will say that for my Maine Coon mix Charlie, we just watched the lump for a while. It did not change size for three months. My vet said that if it is stable, it is less likely to be something urgent. I think FNA is a good first step because it is quick. I read a thread earlier Charlie's growth on his flank where someone said the same thing. I would rather not cut a cat open if I don't have to.

Look, I'm a mechanic. If you want to know if a part is bad, you take it off and look at it. FNA is like poking it with a stick. Sometimes the stick gets stuck or you only see the surface. My Rocky had a bump Rocky's mystery bump and the vet did an FNA. Said it was nothing. I trusted him, but I would have preferred a biopsy just to be sure. But then again, Rocky is hyperactive and getting him sedated for a biopsy is a nightmare. So I went with the easy route.

Oh wow, this is serious stuff! I hope everyone's cats are okay. My maine coons Loki and Freya are very lucky not to have any lumps. I remember when I was looking up info for a friend's cat, I found this thread FNA vs Biopsy discussion that had some really good stats. It said that for inflammatory masses, FNA is pretty good, but for neoplasms, it can be tricky. I think it depends on the location too. If it's easy to reach, maybe FNA is fine?

@vhoward Thank you for the data point. That is exactly the discrepancy I am worried about. A false negative is the primary risk.

@mike_m67 The sedation risk is a valid variable, especially for older cats. I am considering that for Vera.

Does anyone have experience with the specific protocol for the procedure? I am worried about the stress on my cat. I found some tips here How to prep a cat for a vet visit that seem useful, but I am not sure if they apply to a cat with arthritis.

I saw this thread Rex's lump and the vet's advice earlier where a guy was worried about leaving his cat alone for the procedure. I think that is a separate issue. For the accuracy question, I still think we need more anecdotes. Has anyone had a case where the FNA was correct and the surgery wasn't needed?

i have a thread up with the details on what worked for us in the end. Olive's weird skin bump it explains the whole process from the first fna to the final diagnosis. i think it answers your question about reliability better than just guessing. take a look there.