Cutaneous malignant melanoma in an 11-month-old Russian blue cat

Abstract

CASE HISTORY: A grey mass developed on the tail base of an 11-month-old Russian blue cat. The mass grew slowly for 2 months and then became ulcerated. CLINICAL FINDINGS: The mass was excised, and histology revealed it to be a malignant melanoma. Skin adjacent to the melanoma and underlying tissue contained large aggregates of melanin and numerous melanophages. Seven months later, an additional malignant melanoma was excised from the skin on the left thorax. Three months after the second melanoma was excised, the left axillary lymph nodes were enlarged; four were excised, and found to contain metastases. The cat became lethargic and anorexic, and was subject to euthanasia at 26 months of age. Post-mortem examination revealed numerous small well-circumscribed melanomas scattered within the S/C tissue overlying the left thorax and within the left axilla. These were interpreted to be in-transit metastases. Metastatic foci were also visible within the spleen, liver, lungs, lymph nodes and a rib; numerous small melanomas were also present throughout the mesentery. DIAGNOSIS: Cutaneous malignant melanoma with numerous distant and in-transit metastases. CLINICAL RELEVANCE: Although cutaneous malignant melanomas appear to be rare in young cats, they can display a similar clinical behaviour to malignant melanomas in humans, and a guarded prognosis should be suggested for neoplasms of this type. In humans, in-transit metastases are a well-recognised consequence of removing lymph nodes that drain areas containing neoplastic disease. This manifestation of metastatic disease has not previously been reported in the veterinary literature.