When Rob noticed a tiny red lump on the inside of Poppy’s foreleg, he didn’t worry too much. Maybe she had bumped herself, or been bitten by an insect. It was such a small lump that he didn’t think it was anything to worry about, but to be safe, he decided to keep an eye on it.
The lump wasn’t worrying Poppy at all – it wasn’t itchy, and she wasn’t scratching at it or licking it. But over the following ten days, Rob could see that it was gradually getting bigger. When it reached the size of around a centimeter in diameter, and half a centimeter in depth, he decided that it was time to visit the vet.
When I checked Poppy, I could see that she was a young adult Golden Retriever in her prime. But the small lump was worrying: it is a type of tumour sometimes called a “button tumour”, because it looks like a little button, tightly attached to the skin. It was definitely in the skin itself, and it could be moved around easily over the underlying structures of the leg: in other words, it was not attached to anything beneath the skin, such as muscles or bones. In the world of tumours, this is a good thing: it means that it’s less likely to be sinister and if surgery is needed, it’s a much easier operation.
This type of small, button tumour in a young dog is usually benign. The most common type is known as a “histiocytoma”: it’s a harmless proliferation of connective tissue cells in the skin. Many histiocytomas go away by themselves after five or six weeks although sometimes they are surgically removed to hasten return to normal and to remove any small risk.
The problem is that a small proportion of button tumours are more sinister. There is a malignant tumour known as a “mast cell tumour” that can look exactly like a histiocytoma. Benign tumours can be safely left alone, whereas malignant tumours need to be removed promptly to avoid any risk to the animal’s life. For this reason, whenever I see this type of skin lump, it’s important to do a simple test to ensure that it’s definitely benign.
The simple test involves taking a biopsy known as a Fine Needle Aspirate (FNA). A sharp needle (of the same type usually used to give injections) is pushed into the lump, collecting cells in the hub of the needle. These are then squirted onto a microscope slide, and sent to the laboratory. A pathologist then stains the slide, and examines it under the microscope. By looking at the cells under magnification, it’s easy to tell whether they are benign (like a histiocytoma) or malignant (like a mast cell).
I took the biopsy from Poppy during a normal consultation: no anaesthetic or sedation is needed for good natured dogs like herself. The result came back two days later and it confirmed that this is definitely a histiocytoma. If it had been a mast cell tumour, the pathologist would have seen a different type of cell under the microscope, and we would then have had to take radical action, cutting out the tumour with a wide margin around it.
As it is, no action is needed other than simple monitoring. Rob will carry on watching the lump, and it will probably go away over the next month. Even though we know it’s benign, we’ll still all be happy to see the little red button disappear.
- Skin lumps in dogs can be benign or malignant
- A simple biopsy is the best way to find out
- All tumours are easiest to deal with if treated promptly