If only we could politely decline the lumps and bumps that so often show up on our dogs and cats as they age! Last week I wrote about cloudy eyes and how frequently pet owners ask me if their pets are going blind. Questions about lumps are probably just as frequent. The most important take-away from this post is this: if your pet develops a lump under the skin, in any location on the body, please have your vet check it out, preferably sooner than later! Your vet will be able to determine if the lump is benign (harmless) or cancerous, usually by performing a test called fine needle aspirate. This test can be done in the office with your pet fully awake and only involves a tiny prick of a needle to obtain cells from the lump.
The most common lump we diagnose in dogs, and less so in cats, is a fatty lump called a lipoma. They feel like soft, movable bumps under the skin, and you may find them when you are bathing or grooming your dog. They aren’t painful and usually grow slowly. When we aspirate a lipoma with a needle, the cells that come out tend to feel greasy if you rub them between your fingers. On a slide under the microscope, the cells look round and clear. If we diagnose a lipoma, there generally isn’t an urgent reason to remove it surgically, unless the lipoma is growing rapidly, especially in a location that causes irritation or inhibits movement (such as the armpit or groin). More rarely, lumps called infiltrative lipomas or liposarcomas may develop. They are much faster growing and tend to invade the local tissue, including muscle and bone. Surgery is required and is often followed with radiation if the lump cannot be completely removed.
Up to 20% of skin lumps in dogs are called mast cell tumors. Mast cells are part of the immune system, but when they grow uncontrollably in a location, a mast cell tumor develops. Boxers, Bulldogs, Boston Terriers, Labs, Golden Retrievers, Schnauzers, and Cocker Spaniels are all breeds with higher risk for mast cell tumors. Mast cells contain chemicals such as histamine, and sometimes dogs with mast cell tumors will be itchy at the location of the lump. If a fine needle aspirate shows your dog has a mast cell tumor, it’s important that it be graded to determine the best course of treatment and the expected outcome. Grade 1 mast cell tumors are diagnosed about 50% of the time and are the least dangerous. Grade 3 mast cell tumors are diagnosed a quarter of the time, and if only surgery is used without chemotherapy, mean survival time is 4-5 months. Cats can also develop mast cell tumors, typically at an older age. Feline mast cell tumors are divided into well-differentiated and poorly-differentiated, with the former acting benign and the latter being more aggressive. Treatment for cats involves surgery, with radiation following if the lump cannot be completely excised. One final comment about mast cell tumors: they can also develop internally as well as in the skin.
Fibrosarcoma is another type of skin lump in dogs and cats that can occur spontaneously or due to infection with a virus. Fibrosarcomas are generally difficult to treat, because the cells tend to spread out like fingers from the main tumor. This makes complete surgical removal impossible in some cases. Radiation and/or chemotherapy are used following surgery to combat cells that have been left behind. Unfortunately, a specific type of fibrosarcoma associated with injections (including vaccines, steroids, and other drugs given under the skin) has been documented in cats, affecting anywhere from 1 in 10,000 to 10 in 10,000 cats. Fibrosarcomas following injection typically take years to develop and are difficult to treat. Vets are advised to follow certain steps to prevent injection-associated fibrosarcomas in cats, including: 1) using non-adjuvanted vaccines, 2) limiting vaccinations to only those necessary (see my prior post about feline vaccination), 3) giving injections of vaccines in standard locations, mainly low on the limbs, and 4) recording the location of injections and manufacturer and lot number of vaccine or drug injected. Recently, a study was published advocating tail injections in cats. The idea is that if a cat develops a fibrosarcoma following injection of vaccine or drug under the skin of the tail, the growth could be removed via tail amputation. This is a better scenario for the cat than losing a leg to amputation. According to the study, injection under the skin on the tail was well-tolerated. I must admit that although I like the theory behind tail injections, I haven’t yet been brave enough to try it. I think when I do, I will have an experienced person holding the cat for me, since the tail is a rather movable piece of anatomy!
One other lump that is worth mentioning is actually a part of the dog or cat’s anatomy: the lymph node. In a healthy animal, lymph nodes are not noticeable, even though they are present in numerous locations in the body. Lymph nodes can become enlarged if the body is fighting infection or due to inflammation or cancer. If you are petting your dog or cat and feel lumps under the jaw, in the armpits or groin, or behind the knees in the hind legs, please go to your vet immediately for an exam. Lymphosarcoma, or lyphoma, is a very serious cancer that causes multiple lymph nodes to swell, and eventually the out-of-control lymph cells invade the bone marrow. The sooner treatment begins, the better the chance for remission, which can be achieved in approximately 3/4 of patients using chemotherapy. How long remission lasts depends on the chemo protocol used and other factors.
That’s a wrap on lumps and bumps on our senior pets. I urge you to make a habit of running your hands over your dog or cat’s body, at least every couple of weeks, to catch any new lumps that may arise. If you feel any, please get it checked out at your vet’s office. If your dog or cat has a lump the has already been checked, and suddenly that lump starts growing quickly or the hair falls outs or the skin breaks open, this is another reason for a vet exam. Sudden changes such as this often mean the lump is not behaving in a benign manner and surgery may be needed.