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What is this lump?

I had two lumpy patients this past week. One, a 6-year-old happy male neutered mixed breed dog, the second a 15-year-old male neutered domestic short-haired cat. Both of them had the same type of lump - presenting on the same day. Very bizarre or coincidental.

The first pup I picked the scab off this lump and underneath it extruded pasty material that I thought was consistent with thickened sebaceous material or sebum, kind of like a blocked pore, or follicle but without the inflammation associated with a pimple. Since he is young, it’s less likely to be neoplasia or cancer. But, I discussed with the owner about having him in for a dental cleaning and performing an excisional biopsy at the same time. The owner declined and elected to monitor.

That afternoon came, and in with a cat with a new lump. Now a 15-year-old cat can have cancer easily, so for this case. I did the same, picked off the scab, some of the material extruded was waxy and pasty, just like the dog lump, but this one I smeared onto a slide to have a look.

These dark stained cells with irregular edges are keratinocytes. They are usually anucleated. Keratinocytes of the superficial skin with no nucleus are normal. However, I started to see some cells with a nucleus. Now, steps to see if this means cancer are to check for multiple nuclei in a cell, if the nuclei have chromatin that is lining up for cell division - these mitotic figures suggest rapid cell division labeling it as cancerous, or multiple darkly stained nucleoli. We may also see cells of a heterogenous population, or anisocytosis - cells that vary in size, or anisokaryosis - cells that have nuclei that are variable in size.

So let’s take a look.

I see a few cells that have multiple nuclei. So far I know it’s epithelial in origin.

I didn’t see anything that looked like a mitotic figure, but I'm not a pathologist. This lump could still be benign. The best way to know if a lump is benign or malignant is to take a biopsy. Often for these small cutaneous lumps I will do an excisional biopsy, which means that the lump can be completed excised and sent whole to the pathologist. So far my favourite technique is to use a punch biopsy tool that is just larger than the lump, and close the skin with non-absorbable suture. It’s super fast. Don't forget to the stain the edges so that when the sample shrinks in the formalin, the pathologist knows where the edge is. Biopsies give you more answers than these fine needle aspirates that I can take on an awake patient. I can get histology and the pathologist can tell me if it’s a bad cancer, or if I had a curative biopsy that allowed for wide enough margins that I would not have to repeat the surgery, and the lump is unlikely to grow back. If you didn’t get clean margins, your suture is still there to mark where you can now go for 3 cm margins and one fascial plane deep, if needed.

So what did we do for this cat? The owner says she doesn’t want to put her cat through anything invasive. So, this owner also elected to monitor. However, the difference between the two cases, being signalment, made me set a follow up call for the cat. I will call to ask if the lump has grown, are there any more lumps? Is the lump changing colour or texture at all? I will then put together an estimate of cost for a quick sedation and biopsy, because this is fairly non-invasive. Lumps are important to get while they are small, then they are so much easier to remove. As always, I will keep you posted if anything else comes up!

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