Lumps on dogs are usually benign, but not always


This seemed to be the Week of Little Lumps around here. “Hey Doc, would you check this thing on Broomhilda’s ear (nose, leg, side)?” clients ask. “It’s been there a couple of weeks (months, years).” I’m always happy to oblige.

The growths in question usually fall into several categories. Some are tiny hairless bumps, like smooth split peas on the surface of the skin. Others protrude like miniature fronds of cauliflower, or dangle by stalks like a grape on the vine. Still others are harder to delineate but feel like thickenings in the skin beneath the fur. Of course when an owner finds such a growth, the big fear is the big C. Is it cancer?

In these litigious times, we must start with a disclaimer: without a biopsy, it is impossible to say with 100 percent surety that Broomhilda’s growth is not cancerous. Let’s define our terms. A biopsy involves cutting a piece of a growth and sending it to a laboratory where the tissue is fixed, sliced into incredibly thin sections, stained, and evaluated under the microscope by a board-certified pathologist. A biopsy can be “excisional,” meaning we remove the entire growth for biopsy, or “incisional,” meaning we just cut out a little piece of it.

Now let’s define “cancer.” Here’s where it get’s tricky. People, even veterinarians and other health professionals, do not always use the terms for such growths in the same way. The word tumor comes from the Latin tumere, meaning “to swell,” and originally was used to refer to many different kinds of swelling. Nowadays, however, the word tumor is used primarily to refer to neoplasms. The word neoplasm is derived from the Greek neo meaning “new” and plasm meaning “something formed.” So a neoplasm or tumor is a “new formation,” i.e., an abnormal growth of new tissue. But not every abnormal growth of new tissue is necessarily what most people think of as “cancer.” A wart is an abnormal growth of new tissue, but doesn’t send every witch running to the oncologist.

Hence we come to the concept of benign and malignant. Essentially, a benign tumor is one that does not spread to other locations, does not grow indefinitely, and does not invade local tissue. When we say “cancer,” most people are thinking of malignant tumors. Malignant tumors can act in many different ways, depending on the specific kind, but the fundamental concept of what defines malignancy is a tumor that may grow indefinitely, become progressively more invasive, and has the potential to spread to other parts of the body. The word “cancer” comes from the Latin for crab and refers to this invasive and metastatic spread.

All of this is prologue to telling you that odds are Broomhilda’s little growth is nothing to worry about. Is it “abnormal new growth?” Well, yes. Is it a tumor? Well, in some cases, technically, yes. But is it cancer? Probably not in the way you mean.

One common growth veterinarians see are papillomas, those things that look like teeny fronds of cauliflower. Caused by a virus, papillomas are benign tumors. In young dogs they tend to occur in and around the mouth. They are contagious to other dogs, but generally regress spontaneously in three to six months.

A different form occurs in older dogs, particularly in Cocker spaniels, affecting the head, eyelids and feet. In older dogs, however, many of these wart-like growths are sebaceous gland tumors. Sebaceous glands are microscopic structures in the skin that secrete an oily substance called sebum that moisturizes the skin and fur. Older dogs frequently develop changes in these glands. Broomhilda’s little “wart” can be one of any number of specific growths including nodular sebaceous hyperplasia, sebaceous epithelioma, and sebaceous adenoma (all of which are benign) and sebaceous carcinoma (which is malignant). The problem is that these all can look identical to the naked eye. Do we really care which type it is? Well, maybe.

Only about two percent of sebaceous tumors are malignant, and I suspect the real percentage is far lower, as the vast majority of such growths never get biopsied. Even if Broomhilda does have a malignant sebaceous carcinoma, these do not tend to spread to other parts of the body and are often easily cured by simple surgical removal. When should we absolutely remove or biopsy such a growth? If it is growing very rapidly. If it keeps getting irritated. If it gets in the way of grooming. If it ulcerates and bleeds frequently. But if it is just sitting there doing nothing, then I usually play the odds, assume it is benign, and do nothing, too.

Another common skin lump is the “keratin inclusion cyst.” Also know as follicular cysts, these are not tumors but sac-like structures that form from a part of the hair follicle, and fill with a thick white, grey, or yellow cheesy material. Your veterinarian may poke a lump with a needle and squeeze it gently to see if it contains such material. These cysts can occur spontaneously or be the result of trauma or irritation. They are occasionally associated with hair follicle tumors. If infected or inflamed, or your veterinarian has a high suspicion of concurrent tumor, surgical excision may be advised, but in general no treatment is needed for these cysts. Other benign growths can range from minute skin tags, to lumpy nodular fibromas, to dangling grape-like masses called collagenous nevi.

Let your veterinarian take a peek at Broomhilda and help you decide if that little lump is worth worrying about. Your veterinarian may advise a “fine needle aspirate” which is a diagnostic tool not as definitive as a biopsy, but not requiring anesthesia. Sometimes a growth can be easily biopsied or even removed with a local anesthetic. But many of these benign growths do not require treatment. They are common in older animals and I think we may even be wrong to call them “abnormal.” With age may come wisdom, but with age also come warts.