Liz Buchanan BVSc MRCVS
Hello! Very often when they go to the vets, people want clear, direct, simple guidance and this is what your vet has given. It sounds like you're the type of owner who'd like to hear a few more of the pros and cons - thats ok, you can ask them! Here is my best guess.... imagine there is a lego model. You dont know what the model is of. You can put a needle into a lump - that's the equivalent of being handed a few random bricks (cells) to look at, out of context of the other peices. But if you take a few bricks and they're all red, you can't conclude 'there are only red bricks in this model.' You might have just blindly taken your red bricks from the zig-zaggy bit on the back of a green dragon's tail. Similarly, you dont know how those red bricks are related to each other - what pattern they were built in. Are they a dragon, or a dog, or a horse? Nor do you know how those cells were arranged. So although you might happen to get an obvious cancer cell, you can't necessarily say with much conviction that it isn't a cancer. You might not be able to identify it. I once, as a very junior vet 20 years ago, put a needle into a swollen lumph node and got back many, many mast cells. This suggests a mast cell tumour and thats what I diagnosed. But we now know that you can also get lots of mast cells for other reasons, such as a certain type of reaction to a foreign body, and this is what had happened in this case. To my pleasure but also embarrassment, the atient got better. Gradually, with combined experiences of this type, it was realised that a very few cells arent as useful as taking a small peice of tissue, which shows how the cells relate to each other - and that even this isnt as useful as taking the whole lump (with a wide margin if we are concerned about sideways spread). These days, we therefore weigh up what we're looking for - if we're looking just a type of cell, then FNAs are the best. But if we need to know the structure of those cells (are they clustered around a foreign body, or are they coming out of the lymphatic drainage system?) then a larger sample will give more context. This is for the individual vet to decide in the individual patient.