It’s a Bump, It’s a Lump, But Is It Cancer?

As a pet owner, particularly with dogs, sooner or later you will notice a lump on your pet. Should you get worried and rush to your veterinarian, or should you just ignore it and do nothing about it?

Let’s talk about what those masses could be and make a decision together.

Most common masses encountered on pets tend to appear as they get older. Lipoma or fatty cell tumors are high on the list. They are usually on the smaller side (one to three centimeters in diameter), fairly movable, subcutaneous (under the skin), round, and soft. 

Another common growth is a cyst. Cysts tend to be quite small (only a few millimeters in diameter), they can be pigmented (dark) or pink, they can be smooth or irregular and they can protrude through the skin and sometimes rupture. This is when pet owners will notice a whitish discharge.

The problem is that malignant tumors can have a very similar presentation. You or your veterinarian will not be able to diagnose a mast cell tumor, Cutaneous Hemangiosarcoma from a Lipoma by simply looking at it.

In order to correctly diagnose the lump as a benign or malignant tumor, your veterinarian has to actually perform a biopsy. Often time, your veterinarian will simply use a needle to aspirate a very small sample. This procedure is called a "fine needle aspirate." In the case of a Lipoma (fatty cell tumor), the sample will contain fat droplets and no cell. In the case of a mast cell tumor, mast cells will be present.

Unfortunately, some malignant tumors do not exfoliate (i.e. shed cells). When dealing with those tumors, an incisional biopsy or punch biopsy (a “chunk” of the tumor needs to be biopsied) is necessary in order to get a diagnosis.

In the human field, this is often performed under a local anesthesia, and the fragment removed is then sent to a lab for review by a pathologist. With our pets, this procedure can be quite costly and challenging as most pets don’t stand still long enough to allow your veterinarian to obtain the sample. This is the reason why, in veterinary medicine, excisional biopsies (where the whole mass is removed and biopsied) are more commonly performed.

The best approach when discovering a lump on your pet is to contact your veterinarian immediately. When diagnosed and removed early, most masses — even when malignant — can save your pet’s life.