Canine Eye Melanoma

" Canine eye melanoma is also called canine uveal melanoma; or dog eye cancer which involves the iris and ciliary body, collectively called the uvea. Dog eye melanoma arises from melanocytes, which are pigment cells which reside in the dog eye uvea. The malignant form of secondary canine eye melanoma is common, where both eyes are involved and that may appear darkened or pink in appearance. Eye melanoma in dogs is characterized by a firm, evident mass with inflammation, hyphema (accummulation of blood in front eye chamber), glaucoma and pain. Diagnostic approaches include the clinical presentation, history, predisposing factors and laboratory procedures that are used for the eyes and for whole body confirmation. Secondary canine eye melanomas always requires a systemic approach toward diagnosis. Treatment is initiated with the management of any symptoms followed by either medical or a surgical mode of treatment. Surgical excision is mostly done due to address any malignancy (cancerous cells). Support and close monitoring of the condition is critically required even after successful treatment. "

Causes/Pathogenesis (disease progression) of Canine Eye Melanoma:

The etiology or exact possible cause of canine eye melanoma is yet to be discovered. This condition may occur in any dog, of any age and breed, but some breeds such as Labrador Retrievers and German Shepherds are genetically predisposed to dog eye cancer.

Environmental and genetic factors are two main etiological components for canine eye melanoma, but it is not understood how exactly these factors cause cancerous development in the eye, specifically as a secondary malignancy. It is assumed that Neoplastic changes (cell changes) occur and result in a melanocytoma (localized benign tumor), malignant melanoma and iris freckle (proliferation of melanocytic cells). 

The benign or less dangerous form of dog eye melanomas, which are also called melanocytoma may take months to years to affect a dog, but delayed symptoms are uncommon. On the other hand, the malignant form of eye melanoma in dogs, which is mostly secondary in nature (caused by cancer in another patt of the body), usually takes only few months to attain a noticable clinical stage.

Recent studies shows that 4% of canine uveal melanomas metastasize or spread, and they do so within 3 months of being diagnosed with the condition.

Symptoms of Canine Eye Melanoma:

Clinically, dog eye melanoma is represented as an obvious mass in the eye along with hyphema (blood on the front surface of the dog eyes), glaucoma and pain.

Dog eye melanoma has two different forms of clinical representation; early and late presentation. In the early stages of eye melanoma in dogs, it appears to be an iris freckle, an obvious spot which usually does not disturbs the anatomy and thickness of the iris, but may be a single freckle or many freckles and is either unilateral (in one eye) or bilateral (both dog eyes).

In another form of early presentation, canine eye melanoma appears to be a dark and smooth, but nodular body on the iris, which does not affect dog eye function. In less common forms of the disease, the anterior (front) portion of the iris may become inflamed and the iris surface becomese severely affected by the uveal melanoma, which is dark and focal and begins to affect the physiology (condition) of the eye.

In late presentation, the anterior portion of the iris is severely affected, where signs of hyphema, pain and glaucoma become prominent. Symptoms of such as blindness, intraocular hemorrhage, uveitis, retinal detachment and protruded eyes due to pressure are noted.

Diagnosis of Canine Eye Melanoma:

Clinical symptoms and the history of eye coloration change along with minor dog eye symptoms such as cloudiness and inflammatory signs should be considered. For confirmation and differential diagnosis, laboratory procedures such as a Slit Lamp examination, goniscopy, tonometry and funduscopy should be conducted.

Canine eye melanoma is usually noted to be secondary and malignant (fast growing and spreading) in nature, therefore a detailed whole body examination through lymph node and biochemical profiling along with detailed chest radiography and abdominal ultrasound should be done, so that the underlying metastatic activity can be revealed.

Through the use of a differential (rules out other possible causes of the dog eye condition) and critical diagnostic approach, dog eye melanoma should be differentiated from uveal cyst, chronic uveitis, genetic iris pigmentation characters and pigmentation canine glaucoma.

Treatment of Canine Eye Melanoma:

A definite diagnosis of canine eye melanoma usually takes longer than it takes for the disease to progress, which is why, the malignant form of the condition causes worsened clinical symptoms within months. Therefore, symptomatic treatment is always initiated after an initial diagnosis. This is done with different anti inflammatory drugs, supportive supplements and regular monitoring and dog eye cleaning.

In latter stages of the disease, a medical or surgical approach is applied to eliminate any cancerous tissues. Dogs with eye melanomas should always be referred to a veterinary specialist or oncologist for a treatment plan. This will include the strict monitoring of progress of any dog eye lesions with followup exams every 3 – 6 months along with specific and symptomatic therapy.

In advanced cases, surgical excision is required, which should be performed immediately on the basis of status of the appearance of clinical dog eye lesions and laboratory reports. Post surgical care and monitoring is required, since malignant forms of tumors can recur. Also, any underlying primary melanomas, found anywhere in the body should also be treated accordingly.

In most cases, it has been noted that canine eye melanomas have been proven to be a clinical representation of primary tumors that are found elsewhere in the body, meaning that the dog eye melanomas are secondary or caused by a tumor outside the affected region.

For added supprt, in addition to the specific therapies recommended by the veterinarian for the elimination of cancersour tissues, it is recommended that an affected dog should be administered supplements and natural remedies. Natural anti-oxidants such as C-Caps have been proven an effective way to reduce the severity of symptoms. Others such as Eye Heal help to improve eye health. Note that these products can be helpful as part of the treatment plan, but are not a replacement for specific treatments recommended by a veterinarian or veteriary oncologist.

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References:

Merck Veterinary Manual (Merck & Co.)

Hendrix D. Diseases and Surgery of the Canine Anterior Segment. (Blackwell Publishing, USA 2007)

Canine Uveal Melanoma with Brain Extension in a Dog

Alba Galán1, J. Martín de las Mulas2, E.M. Martín-Suárez1, A. Raya2, J. Gómez-Laguna2 and J.M.
Molleda1
1 Department of Animal Medicine and Surgery,Veterinary School, University of Cordoba, Spain
2 Department of Anatomy and Comparative Pathology,Veterinary School, University of Cordoba, Spain