As we see dogs and cats age, we must be on the lookout for the development of lumps and bumps on our four-legged friends. The big c-word, cancer, is prevalent as our pets age, but here are some generalities.

My exam room jargon goes like this: There are benign and malignant cancers, meaning cells are growing out of control. Of course, malignant tumors have a higher detrimental effect and worse prognosis. In dogs, we see many lumps and bumps on the skin, and I would say 90 percent of them are benign, such as warts, cysts and fatty tumors (lipomas). In cats, we rarely see masses on the skin, excluding the common abscess occurrence. In contrast to dogs, cat skin tumors — although rare — are malignant 90 percent of the time.

This brings me to the common benign tumor of a lipoma or fatty tumor. Almost all lipomas, which are tumors of adipose tissue (fat), are slow-growing and benign. These tumors are usually permanently cured by complete surgical removal. Rarely, they may keep growing and cause problems because of their size and infiltration of adjacent structures. A few tumors (liposarcomas) are of low-grade malignancy, so they recur locally. The spread to other parts of the body (metastatis) is extremely rare but there is a syndrome of multiple tumors called lipomatosis.

The benign form of adipose tumors is common in dogs, mainly in middle-aged to older animals. The tumors are twice as frequent in female dogs as in male dogs and occur more often in overweight dogs. The tumors are rare in cats, although again are more common in obese animals. Infiltrative adipose tumors are uncommon in dogs and rare in cats. They may occur in young dogs. Most recorded cases have been in Labrador retrievers. Both dogs and cats can have the syndrome of lipomatosis. These tumors usually form a soft lump under the skin, although they also occur within the abdomen. They rarely cause discomfort unless they are large. Ulceration and bleeding are rare but large lipomas may necrose, or die, causing yellow discoloration of the fat within the case of very large ones. I do recall removing from the armpit of a 40-pound dog, a lipoma the size of a football, which impeded the dog from walking just because of the size. It's better to remove tiny tumors before they reach that type of size!

How is this cancer diagnosed?

Clinically, these tumors have a typical appearance, which means they are soft, movable and not adhered to surrounding tissue or muscle. They are not painful. To identify the tumor with more certainty, needle aspiration, punch biopsy, full-excision biopsy or exploratory surgery (for tumors in the abdomen) is needed. Once obtained, the samples will be examined under the microscope, using either cytology or histopathology. Cytology is the microscopic examination of cell samples sucked (aspirated) from the tumor using a needle. The cells put on a slide look just like fat droplets transferred to a drinking glass from handling a piece of chicken fat. In some cases, with the typical clinical appearance, cytology can give reasonable confirmation of tumor identity. Most of these tumors are benign and are cured surgically. The infiltrative type is sometimes difficult to remove. If a tumor is difficult to remove, or if it re-grows after surgical removal, this indicates that the tumor is of this type.

Knowledge is power, and a simple test in the exam room can often guide us to the conclusion that a worrisome lump is in fact benign.

If you have a pet with a lump and are concerned make an appointment with your family veterinarian to have it diagnosed.

Dr. Darren Woodson has practiced veterinary medicine in the Farmington area for more than 28 years and has a passion for educating pet owners. If you have a question you would like him to address, email Please understand Dr. Woodson will choose the questions that are most relevant to our readers.