Is a needle biopsy the proper way to diagnose cat mast cell tumors?

Hi, thanks for using Petco Pet Education Center, formerly Petcoach! It depends on the Vet's experience with reading cytology. Most Vets send out their cytology samples to a specialist who is trained to read them. Mast cell tumors have a classic look and tend to be one of the easier tumors to diagnose. You could ask your Vet to send the slides out since that only takes 1-2 days to get them back but sometimes aspirates do not get you an answer. I know you have surgery set up and a biopsy planned. That is the best thing for Precious, to get the mass off and know what it is. It has a high chance of being benign. It is a good thing it hasn't grown much. I wish you the best!

Hello, and thanks for using Petco Pet Education Center, formerly Petcoach. A needle aspirate is the standard way to get an initial "suspected" diagnosis on a lump, but there are limitations to what a needle sample can tell us. If the cells in the needle sample appear worrisome, then the next diagnostic step is to send in a biopsy (surgical "chunk") of the tumor, or to remove the tumor itself and send the whole thing in to the lab for analysis. So, was removal of the ear necessary? I can't say, I don't know enough about the location or size of the mass. I didn't see the slide from the initial needle aspirate. But if the needle aspirate looked worrisome, and the next step is to remove the tumor or cut a piece of the tumor off, then removing that piece of the ear may have been the only way to find out for sure what the tumor was, and whether surgical removal was curative. Rather than regretting in hindsight that the surgery was done because the histopathology report came back as a histiocytoma, I would be focusing on the good news that Tate doesn't have a malignant mast cell tumor. And removal and lab analysis of the tumor was the only way you could have gotten that news. Hope this helps!

Thank you for submitting your question regarding Milly. I will typically start with a procedure known as a fine needle aspirate. I use a small needle to collect a sample of cells to evaluate under the microscope. This can help to diagnose the mass. It is not as accurate as a biopsy, but it generally gives a lot of information. The cat needs to hold still and cooperate though. So cats are different to draw blood on awake. This may have been why the recommendation was made to anesthetize her and collect all the samples at once. I hope this information helps!

Very small masses can be tricky to get enough of the needle in the mass without going through it. This area of the body can be tricky to get enough margins due to the lack of tissue before you hit bone, and the movement in the joints makes closure difficult. It could be any number of soft tissue masses, including a wart, mast cell tumor, squamous cell carcinoma, etc. If your vet cannot get enough cells for diagnosis with a fine needle aspirate, simply taking a surgical biopsy without removing the entire mass is an option. When we do bloodwork prior to anesthesia, we are checking the liver and kidney values are normal, no anemia or signs of infection, adequate protein levels, etc. we just want to be aware of any issues inside the body to be able to adjust anesthetic protocols.

I’m glad you are getting Sunny help from your vet. MCTs can be very scary. These tumors can be very dangerous and should be removed promptly. Grading a tumor just by a FNA can be very difficult or impossible. I’ve looked at the slides and agree with your vet that a MCT is a definite possibility here. Sending the entire mass so that it is known if it was completely removed is important. Also, there are special stains and viewing criteria that help a pathologist to grade the tumor properly, but I think they need more tissue than just an aspirate.

Poor Precious! I know you are worried about you! Good news is that most mast cell tumors are easily distinguished on an fine needle aspire (FNA). The chances of it being a mast cell tumor is less likely but not completely ruled out. Also, the fact that it hasn't grown much and the cells on the FNA were very similar in size and shape means it is likely benign. I think you are making the best decision to have it surgically removed and tested. Also, it is likely more oval due to some local inflammation secondary to the minor trauma a FNA causes. I hope this helps!

Thank you for submitting your question regarding Dylan. A procedure known as a fine needle aspirate is used to diagnose tumors just below the skin. A small sample of cells are collected from the mass and evaluated under the microscope. If this was not done when the mass was originally called a lipoma then then diagnosis could have been incorrect. If this procedure was performed then there are two things that could have happened. First, I have seen cancerous masses that have fat cells interspersed throughout them. So the sample collected could have only revealed fat cells, while there were mast cells present that did not show up on the slide. The other scenario is that the original mass was a lipoma and a mast cell tumor has grown over it in the past several years. I have seen this happen as well. I hope this information helps!