Canine melanoma is a tumor that originates from melanocytes. It most often affects older dogs and pigmented breeds. Unlike other tumors, the prognosis of melanomas is strongly linked to their location. Thus, melanomas located in the mouth, nails, and fingers have a worse prognosis than melanomas located on the head or forelimbs.
If you want to learn more about melanoma in dogs, don't miss the following article on our site, in which we explain its main symptoms, diagnosis and treatment.
What is melanoma in dogs?
Canine melanoma is a neoplasm that originates in melanocytes, cells present in the epidermis and in the hair follicles that They are responsible for synthesizing melanin. These tumors can encompass the epidermis and dermis, or just the dermis, and can range in size from millimeters to 10 centimeters in diameter.
They usually occur in older dogs (the average age is between 9 and 11 years), with no sex predilection, but there is a breed predilection.
Types of melanomas in dogs
Melanomas can be classified based on different criteria:
- Degree of malignancy.
- Presence or absence of melanin.
- Location.
Depending on the degree of malignancy
Melanomas can be classified according to their degree of malignancy in:
- Benign Melanomas: Account for 3-4% of skin tumors in dogs.
- Malignant melanomas: They account for 0.8-2% of skin tumors in dogs, so they are less common than benign melanomas.
According to the presence or absence of melanin
Depending on whether or not they present melanin pigmentation, melanomas can present as:
- Pigmentless or amelanotic form: 20% of melanomas have a lack of melanin, which complicates histopathological diagnosis.
- Pigmented form: the remaining 80% of melanomas do have melanin.
Depending on location
Depending on their location, they are classified as melanomas:
- Oral: in the oral cavity, including the tongue, lips and gingival mucosa. Canine oral melanomas are the most common.
- Nasal: In the nasal cavity. They are very rare in the canine species.
- Intraoculars: inside the eye.
- Nails: on the nails.
- Digitals: on the fingers.
- Mucocutaneous: at the junctions between the skin and the mucous membranes (oral, nasal, genital, etc.).
- Cutaneous: in the cutaneous system in general.
The prognosis in melanomas is strongly conditioned by their location. Thus, melanomas located on the head (except the mouth) and on the forelimbs are more likely to be benign and, therefore, have a better prognostic value. On the contrary, melanomas located in the mouth and mucocutaneous junction, in the nails and in the fingers have the worst prognosis. Specifically, oral melanoma is a very fast-growing tumor with great metastatic power.
Symptoms of melanoma in dogs
The appearance of melanomas differs depending on their degree of malignancy. In this sense:
- benign melanomas usually present as cutaneous nodular formations, well located, small, pigmented and not attached to deep planes. They usually have a button-like appearance and are very slow growing.
- The malignant melanomas are usually located on mucous membranes, mucocutaneous junctions, fingers and nailsGenerally, they have a more rapid growth pattern and affect deeper tissues. Macroscopically they can be highly pigmented structures (dark brown or black in color) or nodules without pigmentation (pink in color).
The clinical signs associated with canine melanoma depend on the affected area:
- oral melanomas usually go unnoticed initially, although ptyalism (salivation), halitosis, bleeding gums may be observed as they grow, difficulty chewing or swallowing, and weight loss.
- In nasal melanomas it is common to observe unilateral nasal discharge.
- Intraocular melanomas can cause glaucoma (increased intraocular pressure), uveitis (inflammation of the uvea – iris, ciliary bodies and choroids-), hyphema (presence of blood in the anterior chamber of the eye), corneal edema, epiphora (continuous tearing) and conjunctival hyperemia (redness of the sclera).
- Digital or nail melanomas (on the finger or nail, respectively) can spread to the phalanges and produce osteolytic lesions that are clearly seen by radiography. In addition, nail loss may occur.
- In cutaneous melanomas only the presence of a firm nodule may be observed, although occasionally they may occur bleeding ulcers that do not heal. When the wound suffers a secondary bacterial infection, pruritus (itching) often appears in the affected area.
Malignant melanomas that metastasize can cause very different clinical signs depending on the affected organs. The lung is usually the organ most affected by metastases.
Diagnosis of melanoma in dogs
The diagnosis of canine melanoma is based on the following points:
- Clinical diagnosis: including the clinical history (injuries, clinical signs and their evolution) and complete examination of the patient, paying special attention to skin lesions and palpation of regional lymph nodes.
- Cytology: Melanocytes with a variable amount of pigmented granules are observed. Cytology allows an approach to diagnosis, but it is not enough to differentiate the degree of malignancy of the tumor, for which a histopathological diagnosis by biopsy is necessary.
- Histopathology: by biopsy. The histopathological diagnosis tells us the exact origin of the tumor, the degree of malignancy, the mitotic index, the invasive characteristics and the characteristics of the stroma.
- Immunohistochemistry: Although it is a useful technique for the diagnosis of melanomas in dogs, it is not absolutely specific, so it is always must be associated with histopathology.
- Fine-needle aspiration (FNA) of the regional nodes: even if the regional nodes are not enlarged on palpation, a fine water puncture is necessary to rule out the presence of sentinel node metastases (regional metastases).
- CAT: it is the most indicated method to study the presence of distant metastases, especially lung metastases. In addition, to minimize diagnostic errors, it is recommended to combine lymph node puncture with CT to ensure that there are no regional metastases in the nodes.
Prognosis of melanoma in dogs
To determine the prognosis of canine melanoma, it is necessary to carry out a clinical staging of the same. There are four stages, the first being the one with the best prognosis and the fourth being the most serious.
Clinical staging depends on several factors:
- Location: As we have already explained, the location of this tumor is strongly related to the severity of its prognosis.
- Tumor size: the larger the tumor, the worse the prognosis.
- Mitotic index: Indicates the percentage of cells that are in the mitosis phase (dividing). A higher mitotic index is related to a worse prognosis.
- Tumour-associated lesion: Signs of intralesional inflammation or intralesional necrosis worsen the prognosis of melanoma.
- Regional metastasis: in the regional or sentinel lymph nodes.
- Distant metastases: in organs beyond the regional nodes.
As a general rule, the prognosis of malignant melanomas in dogs is usually serious, especially in the case of oral melanomas in dogs. that an overly conservative surgery is performed with an incomplete resection that does not include the underlying bone. However, cutaneous melanomas offer a better prognosis because they tend to be benign. As is logical, the presence of metastases in any location worsens the prognosis, regardless of the treatment started.
How to cure melanoma in dogs? - Treatment
The goal of canine melanoma treatment is to control the primary tumor and reduce the risk of metastasis.
The three most effective tools to deal with the tumor are surgery, radiotherapy and immunotherapy. The choice of a therapy or a combination of them will depend on the clinical stage of the tumor.
- Surgery: Complete surgical excision with wide safety margins around the tumor should be performed. Its effectiveness depends on the size and location of the tumor.
- Radiotherapy: although it is an exclusively local/regional therapy (it is not useful for the treatment of distant metastases), high response rates, with complete remissions in 75% of cases. However, this therapy has two major drawbacks: its high cost and the small number of existing veterinary radiotherapy centers in Spain.
- Immunotherapy: using xenogenic vaccines or drugs that inhibit cyclooxygenase-2 (COX-2). Xenogeneic vaccines enhance the dog's immune response to the tumor, while COX-2 inhibitors counteract overexpression of the COX-2 enzyme in these tumors.
The response to chemotherapy is small and short-lived, so it is usually used when other treatments fail. Unfortunately, the treatment for canine melanoma is not always effective, so there is not a cure in all cases.
Melanoma Prone Dog Breeds
Although it is a neoplasm that can affect any breed, including mongrel dogs, it occurs more frequently in the breeds listed below:
Benign melanomas
The breeds most likely to develop benign melanomas, which include melanomas on the head (except the mouth) and forelimbs, are:
- Manchester toy
- Irish and Australian Silky Terrier
- Vizsla
- Rhodesian Rudgeback
- Chesapeake bay retriever
Malignant melanomas
As a general rule, malignant melanoma is more common in dogs of pigmented breeds, such as the Schnauzer or the Scottish Terrier. Next, we collect in detail the breeds predisposed to each type of malignant melanoma:
- Oral Melanoma: Black Cocker Spaniel, Irish Setter, Boxer, Chow Chow and German Shepherd. In addition, melanomas in the oral cavity are more common in small and medium breed dogs.
- Nail Melanoma: Golden Retriever and Irish Setter.
- Cutaneous Melanoma: Boston Terrier, Scottish Terrier, Cocker Spaniel, Doberman, and Chihuahua.
If you detect any of the symptoms of melanoma in dogs, it is essential to go to the veterinary clinic as soon as possible.
