Skin melanomas occur mostly in the face (especially the eyelids), trunk and limbs.

Behavior

Melanomas that occur in hairy places are usually not malignant, in contrast to those on the transition between skin and mucous membrane. Benign melanomas of the skin are well defined, highly pigmented, small and mobile. Malignant skin melanomas look bigger (> 2.5 cm), grow quickly and can ulcerate. Metastases occur through both the blood and lymphatic systems.

Melanomas that occur on hairy skin make up 5-7% of all skin tumors in dogs. These tumors arise from pigment cells in the epidermis, dermis, structures closely associated with the skin, but mainly arise from the hair follicles.

Prevalence

This tumor type affects mainly dogs between 5-11 years of age (average age 9 years).

Breed predisposition

The following breeds were reported to be at higher risk to develop this tumor type: i.a. Airedale Terrier, Boston Terrier, Cocker Spaniel, Miniature Schnauzer, Doberman Pinscher, Scottish Terrier, Vizsla.

Symptoms

Skin melanomas vary in their appearance. Generally, a melanoma forms one solid lump, and the color of the melanoma can take on a variety of colors, ranging from black to shades of brown, gray, and red.

In general, a thorough general clinical examination is always performed first, with or without a blood or urine test.

The mass itself

Diagnosis can sometimes be difficult because not all melanomas contain pigment (up to 30% of these tumors do not contain melanin). If it can be determined that the punctured mass is a round cell tumor and contains pigment, this is usually sufficient to conclude that it is a melanoma. If this is not the case, a biopsy must be taken for further investigation.

By immunophenotyping (via PNL2 / tyrosinase / Melan A / S100 staining) one can stain typical proteins for pigment cells. If these proteins stain in places where they normally do not occur, it is likely that the mass taken from a biopsy consists of pigment cancer cells.

Estimation of metastases

Local lymph nodes should be pricked or taken a biopsy of. Due to the diverse behavior of melanomas, both X-rays of the bones and lungs and abdominal ultrasound may be appropriate to detect metastases in places other than the lymph nodes. These can also be punctured or a biopsy can be taken.

Surgery

Surgery is the first treatment for treating melanomas on hairy skin. Long-term responses for fractional radiotherapy have also been described.

The prognosis is good if the melanoma is benign, but reserved if the melanoma shows malignant features (spread rate varies from 30-75%).

Several characteristics contribute to the prognosis, such as the breed of the dog, the tumor size, histopathological markers (mitotic index, Ki-67 content, staining for the canine melanoma antigen with monoclonal antibody MAB IBF9) and penetration into the surrounding tissue.

Race

Depending on the dog's breed, melanoma may behave more favorably / malignantly. For example, it was found that 75% of the melanomas in Dobermanns and Miniature Schnauzers are benign, while 85% of the melanomas in Miniature Poodles are malignant.

Tumor size

Malignant skin melanomas of <4 cm show significantly better survival time than tumors ≥4 cm (12 months vs 4 months) and after 2 years, 46% vs 0% of these dogs are still alive.

Histopathological markers

The proliferation marker Ki-67, which indicates how fast the cancer cells divide, has a higher predictive value for the biological behavior of skin melanomas than classical histology.