Growths on the skin aren't always cancerous
When Sammy the terrier came to see me recently, his owner was worried. A number of strange-looking growths had sprouted around his muzzle and eyes. His owner was sure that this was a type of skin tumour and that his days were numbered. Is there any way I could help?
Skin tumours are the most common "lumps and bumps" seen in pets, and like all tumours, they come in two versions: benign tumours, which are harmless, and malignant tumours, also known as cancer, which can have life threatening consequences. One of the big challenges for vets is that it isn't easy to tell if a skin tumour is benign or malignant by just looking: some sort of biopsy is usually needed.
When I looked at Sammy, there were around a dozen raised areas on his skin, and there were a few aspects of the lumps that were distinctive. First, they were mostly around his head and ears. Second, there were all oval or circular. And third, they had all come up in the past month. It would be rare for cancer to appear so suddenly, so dramatically, and in such a localised area. But still, it was impossible for me to make a precise diagnosis. As is so often the case, some samples needed to be collected and sent off to the laboratory.
I gave Sammy a sedative, and when he was sleeping peacefully, I used local anaesthetic to completely numb the area around one of the lumps, and I used a tiny sharp instrument like a small apple corer to remove a circle of tissue around 3mm in diameter. This would be enough for the laboratory to examine in detail under the microscope. I also took a swab of the cut edge of the biopsy to be cultured by the laboratory. I closed the small hole; when Sammy woke up, he didn't know that anything had happened.
A few days later, the result arrived from the laboratory, confirming what I had suspected. The lumps weren't some sort of strange cancer: instead, they were an unusual form of ringworm. Treatment was threefold: a medicated shampoo twice weekly, some anti-fungal cream to be applied twice daily, and some oral medication to have in his food for a month. His owner's fear of cancer had been unwarranted, and Sammy made a full recovery.
This seems like a simple story, but it might not have had such a happy ending. I remember another case - a Collie - which had a close resemblance to Sammy's presentation. This time, however, the oval lumps were on the dog's underside, which is a less common place for ringworm. Again, I sent off a biopsy sample, but that time it was bad news. The lumps were caused by a skin-focussed version of a cancer called Lymphoma. Treatment was started, using a simple form of chemotherapy, but the poor dog did not respond well, and more lumps started to appear. Additionally, he started to be unwell in other ways: the cancer had started to affect his internal organs. The unfortunate dog had to be euthanased before he began to suffer too much.
These two cases are classic examples of the challenge faced by owners and pets when dogs develop lumps on the skin: benign and malignant causes can superficially appear very similar, yet they can have dramatically different outcomes.
The key to the issue is the common theme of both stories: having samples analysed by the laboratory. While it's sometimes possible to have an educated guess at a diagnosis from just examining an animal, in most cases, detailed biopsy analysis is needed.
The laboratory process is interesting. First, the tiny sample is soaked in formalin, which preserves the cell structure. Next, the simple is sliced into pieces, like a loaf of bread being cut into slices. Then some of the slices are placed onto glass slides and stained with special stains that show up different types of cells in a range of distinctive colours. Finally, a trained pathologist examines the slides under the microscope. Every different disease process produces specific changes at a microscopic level, allowing an accurate diagnosis to be made. Is it infection or tumour? Benign or malignant? If malignant, how serious is it? The pathologist can answer all these questions, giving the vet the information needed to give the pet the best possible treatment.
A full biopsy - obtained by a minor surgical operation - is the best way to make a diagnosis, but vets often use a simpler approach, called a Fine Needle Aspirate. This can be done in a conscious animal, during a normal consultation. A fine needle - the same type that's used to give an injection - is pushed into a lump, then withdrawn. The contents of the hub of the needle are then squirted onto a slide, which is sent off to the lab. The pathologist stains the slide directly, and by looking at the cells, a broad diagnosis can often be made: it isn't as accurate as a full biopsy, but it may be enough to make a treatment decision. If "just fat cells" are seen, this suggests a benign fatty tumour that can be left alone. If instead, "malignant cells" are seen, the vet then knows that the lump must be removed.
Laboratory work adds significantly to the cost of visiting a vet, but in many cases (like Sammy), the results can be reassuring, and they allow your vet to give your pet the best possible treatment.