Melanoma isn't a condition many dog owners worry about, but skin cancer is actually a significant threat to our dogs. Here, our Enterprise vets discuss the causes, signs, and treatment of melanomas in dogs.
What Is Melanoma in Dogs?
Melanoma is a cancer that happens as a result of the unregulated proliferation of melanocytes, a cell that resides in the skin and mucus membranes of mammals. Older dogs are especially prone to this cancer, particularly to its highly aggressive oral form. Melanoma of the mouth accounts for almost 40% of all oral tumors seen in dogs.
If you find something suspicious on your dog, it's always best to err on the side of caution and take your dog to the vet for a full examination as soon as possible.
Types of Cancer Seen in Dogs
Dogs can develop many of the same types of cancer as people, and treatment is similar also. Below are 3 of the most common skin cancers found in dogs.
Squamous Cell CarcinomaSkin squamous cell carcinoma is the most commonly diagnosed form of skin cancer in dogs. This form of dog skin cancer typically affects older animals and is often seen in Dalmatians, Beagles, Whippets, and white Bull Terriers. Squamous cell carcinoma appears as raised wart-like patches or lumps that are firm to the touch. These tumors are most often found on the dog's head, lower legs, rear, and abdomen. While sun exposure may be linked to squamous cell carcinoma, there could also be a link to papillomavirus.
Malignant MelanomaMelanomas appear as raised bumps that can be dark-pigmented (but not always) and are often found around the dog's lips, mouth, and nail bed. Many melanomas are benign, however, they can be malignant. Malignant melanomas grow quickly, have a high risk of spreading to other organs, and are a serious threat to your dog's health. The risk of developing melanomas is higher in male dogs than females and certain breeds such as Schnauzers and Scottish Terriers also face an increased risk.
Mast Cell TumorsMast cell tumors are common cancer found in dogs and occur in the mast cells of the dog's immune system. These tumors can grow anywhere on your dog’s skin or body, including the internal organs however, some of the most common sites for mast cell tumors are on the chest, limbs, and lower abdomen. This form of skin cancer is most commonly seen in dogs between ages 8 -10 years old and certain breeds, including Boxers, Pugs, Rhodesian Ridgebacks, and Boston Terriers appear to be at an increased risk of developing this form of cancer.
Types of Melanoma Seen in Dogs
4 types of melanoma have been found in dogs.
On average, 80% of melanomas we see in dogs will be in the dog's mouth. They are typically seen in dogs ages 10 years and older, and small breeds are at a higher risk of developing melanoma. Miniature poodles, cocker spaniels, chows, and golden retrievers are the most likely breeds to be affected, although any breed can be diagnosed with melanoma.
These tumors can be quite invasive, extending into underlying soft tissue and bone. Although many oral melanomas will exhibit dark pigmentation and appear black in color, this is not always the case. Some tumors may be pink or exhibit mixed coloring. Additionally, not all melanomas will present as a distinct mass. Some will present as more of a flat plaque lesion rather than a mass.
Oral melanomas are considered aggressive tumors and typically exhibit a high rate of metastasis to local lymph nodes and the lungs. Even with complete removal of the local oral tumor, approximately 80-85% of dogs with oral melanomas will go on to develop metastatic disease.
The second most common location is the nailbed or subungual crest. These occur in 15-20% of dogs, again as a solitary lesion. Dogs often limp on the affected foot, or the owner has noticed swelling, bleeding, or discharge from the affected toe.
Subungual crest melanomas behave much like oral melanomas, with a metastatic rate equivalent to tumors located in the mouth.
Dermal melanomas most often appear as a darkly pigmented dermal mass and can be one or multiple. In rare cases, dermal melanomas may invade more deeply into the tissues or, even subcutaneous melanomas may occur.
Dermal melanomas confined to hairy skin are benign in many cases and are therefore cured with complete surgical removal. Tumor location and a biopsy report will help in determining if additional therapy would be required following surgical removal.
Melanocytic tumors can also affect the canine eye as eyelid and conjunctival masses. While many ocular melanocytic tumors in dogs are often benign, they can cause problems for the eye as they grow. Most conjunctival and some eyelid and uveal melanomas are malignant. Malignant melanoma in other places of the body also has the potential to metastasize to the eye.
Diagnosing Skin Cancer in Dogs
If your vet suspects that your pup could have skin cancer they may perform a fine needle aspiration to take a small sample of the tumor's cells or perform a biopsy to take a portion of the tumor's tissue for examination. These samples are then sent to a lab to be analyzed by your vet to provide you with an accurate diagnosis of your dog's health condition.
Following the initial diagnosis of skin cancer, additional diagnostic testing to determine the extent of cancer in the body can help your veterinary oncologist to optimize treatment and more accurately predict prognosis.
Treating a Dog's Skin Cancer
Many dogs diagnosed with early-stage skin cancer can be treated successfully and go on to live full active lives.
Several different therapies or treatment combinations can be used to treat skin cancers in dogs, including surgery, chemotherapy, immunotherapy, targeted therapies, or palliative care when appropriate. Your dog's prognosis following a diagnosis of skin cancer depends on several factors, such as the type of tumor, the tumor's location, and how advanced the cancer is.
Monitoring Your Dog's Health
Detecting the signs of skin cancer while the disease is still in the early stages is the key to good treatment outcomes. Familiarizing yourself with all your dog’s lumps, bumps, and rashes, during your regular grooming routine, as well as visiting your vet for routine wellness exams twice yearly can help to catch skin cancers in the early stages.
If you notice an unexplained or unusual lump or bump on your dog, or if you notice swelling around your dog's toes contact your vet.