The Dog Cancer Survival Guide (118 page)

Tumors treated aggressively and early are generally responsive to treatment. The smaller the tumor is when it is first found, the better the prognosis, which is why early detection is so important. Surgery is a must for oral melanomas, although radiation therapy can also be very helpful. Due to the high risk for metastasis, systemic therapy is also an important part of the treatment plan. A promising and exciting treatment option is immunotherapy, specifically the canine melanoma vaccine which is available through boarded oncologists. Chemotherapy used to be common for these tumors, and may still be considered to control distant metastasis if the vaccine is not used.

Digit melanomas also require an aggressive surgery, with chemotherapy to follow up on metastatic disease. Skin melanoma is usually benign and curable with surgery. For malignant forms, the melanoma vaccine is also recommended to control metastasis.

(I’ll discuss the melanoma vaccine at length later in this chapter.)

If left untreated, oral malignant melanoma has a pretty grim prognosis of only two months survival time. With thorough treatment, dogs with oral tumors can survive one to two (plus) years. Dogs treated for digit tumors can survive two years, and dogs treated for benign skin tumors even longer.

Other names for melanoma include malignant melanoma, melanocytic tumor, and melanocytoma (benign melanomas).

Melanoma develops in the melanocytes, skin cells that are responsible for skin pigmentation. This is a common tumor in dogs, and can occur anywhere on the skin or inside the mouth, so we classify it by where it is located on the body. We’ll discuss the most common types in this chapter.

When you need to look up the definition of a word or phrase, find it listed in
Chapter 5
, which begins on
page 46
.

Oral cancer is the fourth most common type of dog cancer, and oral malignant melanoma (OMM) is the most common oral tumor in dogs. OMM is highly malignant. These tumors are locally aggressive, often invading the bones of the jaw. They also metastasize to the local lymph nodes, liver, lungs and kidneys at rates greater than 60-80%. They appear along the gums, the lips, the palate (roof of the mouth), and the tongue. Oral melanoma should be assumed to be malignant even if the biopsy report suggests otherwise.

The highly pigmented nail bed on the toes is the next most common site for melanoma. Also called subungual melanoma, it is the second most common tumor of the digit in dogs. It is not as aggressive as oral melanoma, with metastasis rates of 30-60%.

Skin melanomas are generally benign in dogs, although malignant forms do develop, rarely. But even benign masses can cause problems, and should be treated.

We know quite a bit about the causes of oral cancer in people – tobacco and alcohol use in particular, and possibly persistent viral infections such as HPV. But when it comes to dogs, we don’t know the cause of oral melanoma. We do know that male dogs get more oral tumors of any kind than females do, including oral melanoma.

Skin melanoma in humans is caused by sun exposure, but the same is not true for dogs. There are some breeds predisposed to skin melanoma, but we’re not sure yet exactly why this is true.

Black dogs with more active melanocytes may be predisposed to melanoma, but dogs of any color can develop the illness. Melanomas are definitely more common in purebred dogs. The benign skin form of melanoma is most likely to occur in Doberman Pinschers and Miniature Schnauzers, while Miniature Poodles are more likely to have the malignant form of skin melanoma.

Poodles, Dachshunds, Scottish Terriers, Cocker Spaniels, and Retriever breeds tend to get more OMM than other breeds. Chow Chows get more melanomas of the tongue. OMM also tends to occur in smaller dogs (of lower weight) than the other oral tumors, and, in one study, German Shepherds and Boxers were at decreased risk for OMM.

Owners usually find melanoma of the skin and the toe by noticing the tumors, which sometimes look inflamed or ulcerated (open and possibly bleeding). They may be very pigmented, or dark, or they may have very little pigment, in which case they are called amelanotic (this is determined by a biopsy).

Much like other oral tumors, the oral melanomas located in the front of the mouth (also known as rostral) are more likely to be noticed by the owner. This early detection means they are often found when they’re smaller, and therefore have a better general prognosis than those located in the rear of the mouth (also known as caudal). Because most owners do not spend much time looking in their dog’s mouth, many tumors are not noticed early. More and more general practice vets are emphasizing the importance of regular home dental care for dogs, which gives me hope for more early detections for oral melanomas.

Symptoms owners notice at home are bad breath, excessive drooling, difficulty in eating or swallowing, pain while eating, pawing at the mouth, bleeding or bloody saliva, loss of teeth, facial swellings or deformities, and weight loss.

If the vet finds the oral tumor during a dental exam or cleaning, he will perform an immediate biopsy. One sign of trouble is if teeth are loose but there is not a lot of tartar or dental disease, for example. In this case, he should biopsy the socket after pulling the tooth, even if there is no visible mass. Most dogs need sedation for thorough oral exams or cleanings, so this is usually done during the same anesthesia used for the dental procedure.

Wherever the melanoma is located in the body, a fine needle aspirate will usually provide a preliminary diagnosis. A biopsy, however, will provide a definitive diagnosis and very important information for the prognosis.

For example, benign skin melanomas are distinguished from malignant skin melanomas by examining how many cells are dividing. This evaluation, called the mitotic index, can be seen in a biopsy sample, and will be very helpful in devising your treatment plan. Note that all oral melanomas are considered malignant, regardless of their mitotic index.

The biopsy sample must be taken carefully because the sample must be large, from the center of the mass, and not from areas filled with dead (necrotic) cells, inflammation, or pus – otherwise the biopsy sample might not represent the whole tumor well, which could lead to a misdiagnosis. Later, it is vital that the biopsy site be included in the surgery or in the radiation field.

In the case of oral melanoma, the biopsy needle can track cancer cells, so it is important to take a sample from inside the mouth, not through normal tissue of the cheek or nasal cavity (for upper jaw tumors). Melanoma can also mimic other oral tumors, making confirming a diagnosis challenging for the pathologist. When this is the case, your oncologist may want to use a special stain for the biopsy, or get a biopsy second opinion.

Because melanoma is so likely to spread, full staging is recommended before treatments are begun. Blood work and urinalysis can tell you how healthy your dog is, in general. Chest imaging (threeview X-rays or a CT scan) can be used to check for lung metastasis, while abdominal ultrasounds can check for spread to the liver, spleen and other organs. Lymph nodes in the region of the tumor should all be checked (aspirated), even if they appear normal, because metastasis is not correlated with normal or enlarged sizes.

“To Others Who are Experiencing What I am Going Through ... It is a breath of fresh air, learning from Dr. Dressler, that Cancer is NOT a death sentence. Every time I see my little one scratching her bed to make it, every time I see her prancing her little girly prance, every time I see her running along the beach, and most of all, every time I look into her loving, adoring eyes, I know without a doubt that nothing that I do for her is ever too much. Everything counts. Every day counts. And when the time comes for us to part, whether it be from cancer, or from age, I know that it will be she that tells me that it is time (but only for a short while, for hope is eternal).”

- Joyce Parham, Julian, North Carolina