Melanoma are a rare and highly metastatic skin disease of cats.

In cats, melanoma account for less than 1% of all feline oral neoplasms and approximately 0.5% of feline skin tumors^[1]. The ocular and cutaneous forms are generally more common than melanoma of the oral cavity^[2]. The most common cutaneous sites are eyes, mouth, dorsal head region, tail, distal extremities, and lumbar area^[3]. The prognosis is generally poor because of recurrence and regional metastasis in up to half the cases^[4]. In a study of 23 cats with non-ocular melanocytic tumours, approximately half were malignant^[5].

A number of variants are known to occur:

1. Melanocytic hyperplasia
2. Melanocytoma – a benign tumor arising from melanocytes, e.g Iris melanocytoma
3. Malignant melanoma – as in humans, highly metastatic and incurable^[6] e.g. ocular melanoma^[7]. Melanoma of the limbus, conjunctiva, and nictitating membrane have also been reported, although they are very rare^[8][9].

Other tumours can look clinically very similar to melanoma, particularly those arising from the skin. These include melanocytoma as well as pigmented lesions of the epidermis and adnexa, e.g., feline basal cell tumour and carcinomas, trichoblastoma, trichoepithelioma, pilomatricoma, sebaceous adenoma, and apocrine neoplasms. Ceruminous adenoma in the feline may be mistaken for multicentric melanoma of the pinna.

Melanocytic hyperplasia (lentigines) on the lips, eyelids, nose, and gingiva of orange, cream, and silver cats appear as pigmented macules at these sites. Hyperpigmented macular lesions clinically resembling melanoma may occur in the skin in dogs, primarily the abdomen and nipple.

Similarly, epidermal hamartomas (pigmented epidermal nevi, canine seborrheic keratosis), and dermal hemangioma and hemangiosarcoma can appear as pigmented cutaneous tumors.

References

1. ↑ Kanai K, et al (2006) Excision of a feline limbal melanoma and use of nictitans cartilage to repair the resulting corneoscleral defect. Vet Ophthalmol 9(4):255-258
2. ↑ Engle CG & Brodey RS (1967) A retrospective study of 395 feline neoplasms. J Am Anim Hosp Assoc 5:21–31
3. ↑ Day MJ, Lucke VM (1995) Melanocytic neoplasia in the cat. J Small Anim Pract 36:207–213
4. ↑ Goldschmidt MH, Liu S-S, Shofer FS (1993) Feline dermal melanoma: a retrospective study. In: Advances in Veterinary Dermatology, ed. Ihrke PJ, Mason IS, White SD, vol. 2. Pergamon Press, Oxford, pp:285–292
5. ↑ Goldschmidt MH, Shofer FS (1992) Skin Tumors of the Dog and Cat. pp. 142–151. Butterworth Heinemann, Oxford, UK, 1992
6. ↑ Day MJ, Lucke VM (1995) Melanocytic neoplasia in the cat. J Small Anim Pract 36:207–213
7. ↑ Patnaik AK, Mooney S (1988) Feline melanoma: a comparative study of ocular, oral, and dermal neoplasms. Vet Pathol 25:105–112
8. ↑ Betton A, et al (1999) Atypical limbal melanoma in a cat. J Vet Intern Med 13:379–381
9. ↑ Roels S, Ducatelle R (1998) Malignant melanoma of the nictitating membrane in a cat (Felis vulgaris). J Comp Pathol 119:189–193