Diagnosis

A physical exam, blood tests, a chest x-ray and a biopsy when the veterinarian believes it is necessary.

Causes

Melanoma arises from melanocytes, cells that impart pigment or coloration to the skin. In humans, melanoma arises due to mutations induced by repeated, intense exposure to ultraviolet light (for example, frequent tanning or working outdoors). This does not seem to be a major factor in dogs, as in most breeds the hair coat affords them protection from sunlight. However, pigment cells divide every time there is injury to the skin, or if there is constant trauma (for example, areas where dogs constantly scratch or lick). Nevertheless, risk factors for canine melanoma are not well established.

Mutations that contribute to cancer can also be inherited. An inherited mutation in a single gene that is important in cell growth control will increase the risk of that individual to develop cancer. This can be due to reducing the overall number of acquired mutations that must accumulate before a cell becomes cancerous, or it can be due to disabling a critical safeguard gene that normally prevents cells from becoming tumors. Specific genes that are responsible for familial melanoma have been identified in humans and in mice. In dogs, there appears to be a predisposition among certain breeds or families to develop specific types of cancer, suggesting that a hereditary component may be important in the development or progression of the disease.