Melanoma is a tumor of the melanocytes, or the cells that create pigment in the body. Because of the affected cells’ job, this tumor is often seen as a darkly colored mass.1
Melanoma often appears in the dog’s oral cavity, the nailbed or digit, the mucocutaneous junctions (areas where the hair-covered areas meet those without hair like lips, vulva, and anal regions), and occasionally in the eye.1,2 Though rare, it is possible for melanoma to develop in other areas of the body as well.
Over the years, specialists have noticed a steady correlation between the location of the tumor and the likelihood of its being malignant (cancerous), a majority of the tumors found in the mouth will be diagnosed as malignant, as well as many of those found in the nailbed. Tumors found on locations of the body where hair grows are often found to be benign. Though these trends are reliable, testing will always be completed when melanoma is found to accurately understand the scope of each individual dog’s case.2
Melanoma can be either benign or malignant, and the diagnosis is done through cytology and biopsy evaluation. The first form of biopsy performed is commonly a Fine Needle Aspirate (FNA) to gather the tissue and examine it. If the FNA does not provide a definitive answer, a secondary biopsy will occur with the surgical removal of a tissue sample.1,4
The staging of melanoma is a big part of knowing what to perform for treatment and to expect as outcomes. Staging of a malignant lymphoma involves checking the most likely affected areas for spread, including the closest lymph nodes, the lungs, and, if necessary, other organs.
Bloodwork will be done to help identify an initial spread. Along with the standard tests, the lymph nodes will have an FNA be taken to check for any signs of metastasis in them. If there are signs of spread in the lymph nodes, the staging tests will continue and the lungs will be examined with radiographs. Staging is defined depending on the severity of the spread and the locations the spread has been found in.
The first sign of melanoma is the development of the tumor. They are usually a darker pigment and can start to bleed or ulcerate as they grow larger.1 There are some melanomas that develop to have a pink-colored mass.3 As we’ve already established, the most common locations to find a melanoma tumor is in the mouth or toes, so regularly interacting with your dog physically in these areas can help identify the growing mass as soon as possible. By regularly brushing your dog’s teeth and paying close attention to cleaning your dog's paws, you can keep an eye out for the signs before they become too dangerous.
A tumor developing in the mouth can create symptoms like drooling, bad breath, blood coming from the mouth, or difficulty or disinterest in chewing hard food. If the melanoma has spread to other parts of the body, signs could be swelling lymph nodes, difficulty breathing, coughing, weight loss, and a poor appetite.3
For both patients with benign or malignant melanoma, the best first step depends on the location of the tumor, but it is usually to perform a complete removal surgery. Removing the tumor establishes a baseline defense over the source of the cancer. The rest of the treatment depends on the level of spread and the impact that the tumor has had on the body as a whole. Radiation therapy can also be a beneficial treatment for dogs who have a more localized tumor. For a majority of cases, chemotherapy is not recommended for initial treatment but mainly as rescue treatment if the melanoma returns.1,4
Dogs that have the entire tumor removed with their first diagnosis are the least likely to see any recurring development of melanoma in their lifetime. Unfortunately, some areas of the body where melanoma tumors can develop can not be effectively approached with a removal surgery. When that is the case, the patient will likely receive a debulking surgery to reduce the amount of cancer cells present in the area, but will also need additional treatment to prevent the remaining mass from regrowing.4
Thankfully, surgery, radiation therapy, and chemotherapy are not a dog with melanoma’s only options. There is also an additional vaccine treatment available to assist in defending the body from melanoma’s regrowth. This supplemental treatment is given through a therapeutic DNA vaccine that brings out an immune response that teaches the dog’s body to fight against melanoma cells.
The addition of the vaccine after completely removing a tumor from a dog that has a Stage II or III oral melanoma has been proven to be effective for preventing local regrowth. The vaccine extends survival time after treatment by 1-2 years. However, the vaccine is only effective as a supportive measure, it has shown no evidence to shrink or prevent growth in a tumor that has not been treated with surgery or radiation.1,2,3,4
As with all cancers, early detection and treatment are major factors in the efficacy of treatment. Dogs diagnosed with Stage I melanoma have significantly longer survival times than those in Stages II-IV. And dogs who receive the melanoma vaccine will have different—often greater—survival times than those who do not.
The average survival times for dogs that have their tumors surgically removed with no supplemental treatment are:
For dogs with Stages II and III melanoma, the vaccine is available to assist after the surgical removal to lengthen the survival time to 1.5 years or longer.3
And of course, the tumor’s location will have an impact on the survival time for the patient as well. Regular monitoring with your vet will help to prevent any surprises from arising after treatment is completed.