In the last column we talked about some of the reasons that those scary looking lumps on our pets may end up being nothing serious, so figuring out what they are can allow you to get some sleep at night instead of worrying that something bad is going on. This column looks at the other side of the coin, the lumps and bumps that can spell trouble and some of the options for dealing with them.

The most common malignant mass I see on the surface of a dog’s skin is a mast cell tumor. These often appear as raised pink lumps that sometimes increase and decrease in size rapidly. Mast cell tumors often look exactly like the benign histiocytomas we talked about last week to the naked eye, but when a needle is used to collect some of the cells from the lump and those cells are looked at under a microscope, the difference in the cells is usually readily visible. The good news about mast cell tumors is that the majority of them can be cured by complete surgical removal. Once the tumor has grown to the size of a softball and has started rotting in the middle it becomes considerably more challenging to remove and has likely had enough time to send out satellite tumors to far reaching parts of the body, making cure with surgery impossible. When the tumor has spread there is not a lot of effective medication or chemotherapy that will help for a long period of time, and death becomes inevitable. Cats get mast cell tumors too, but much less frequently than dogs, and their mast cell tumors tend to be more benign, making them very likely to be curable with removal.

Any lump along the mammary chain in a female pet has potential to be a mammary tumor- the animal version of breast cancer. In dogs about 50 percent of these lumps are benign and can be helped with surgery, and about 50 percent of them are very aggressive, will recur after surgery, and will cause death because there is not much effective treatment for them. In cats mammary tumors are even more likely to be malignant than in dogs. Fortunately, we have a simple way of preventing this problem in our pets. Female dogs and cats that are spayed before they go into heat for the first time (around 7-8 months of age for dogs, and around 6 months for cats) develop mammary cancer at a rate of essentially 0 percent. After a dog has gone into heat two times spaying still eliminates a host of reproductive problems that occur in older age, but it does not convey significant protection against the development of future mammary cancer. It breaks my heart to watch helplessly as an animal, who was never intended to breed, is consumed by mammary cancer just because nobody got around to spaying her for a few years.

When I see a dog come in for "lumps under the chin" I think first about lymphoma. This is the most common kind of cancer in dogs and cats, and in dogs it can cause the lymph nodes near the surface of the body to become very enlarged. A dog will often have a matching pair of firm swellings at the corner of the lower jaw and neck. Further examination often shows that the lymph nodes in front of the shoulders and behind the stifles are also enlarged. Often these lumps appeared over the course of a few days to weeks. Cats tend to hid their lymphoma inside their bodies, so prominent lumps on the outside are not a common tip-off for them. Diagnosis can often be made with a needle aspirate of affected tissue or by removing an affected lymph node and sending it for examination at a laboratory. Even lymphoma has a bit of a silver lining. This type of cancer tends to respond to chemotherapy better than just about any other type of cancer, and most pets tolerate the chemotherapy drugs without the terrible side effects that people often suffer. With aggressive treatment we hope to be able to buy a year of good quality life, but in the end the cancer always wins. Without treatment the average life expectancy with lymphoma after diagnosis is about one month.

This short list is just a few of the more common lumps I see in practice, but there are thousands of things out there that cause visible lumps on pets. Is it a pocket of infection? Is it a parasitic fly larva? Is it glob of fat? Is it cancer? In spite of apparent demand for it, I have yet to develop the skill of determining the composition of a lump over the telephone. But with an examination and a needle we can start getting down to the business of figuring it out and coming up with a plan to deal with it.