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Malignant melanomas tend to be locally destructive, aggressive tumours commonly associated with recurrence and/or metastasis. In this report, a 13-year-old captive white African lioness (Panthera leo), with a recent history of intermittent bouts of lethargy and inappetence, presented with a distended abdomen (due to ascites) and a small, round crusty lesion on the ear. An abdominal ultrasound showed the presence of masses on the liver and an exploratory laparotomy revealed multiple pale lesions on the liver and omentum. Histopathology revealed sheets of pleomorphic neoplastic cells compressing the non-neoplastic liver tissue. Similar neoplastic cells had multifocally expanded and effaced omentum adipose tissue, as well as formed a well-circumscribed mass in the ear sample, extending from close to the epidermis to the lateral and deep margins of the section. All three tissue samples had a high mitotic index (15 per 10 HPF), and critically, in the ear sample, there were rafts of neoplastic cells in the lymphatics, indicating lymphovascular invasion. Immunohistochemistry for the melanoma marker, PNL-2, showed strong positivity in all three tissue samples. Thus, the diagnosis was of malignant melanoma with metastasis to the liver and omentum. This is the first report of metastatic cutaneous melanoma in a lion. [ABSTRACT FROM AUTHOR]

A Himalayan Rex guinea pig was presented with a history of nodular, partially ulcerated masses in the subcutis of the left shoulder. Histological examination revealed a garland-like to nodular, infiltrative neoplastic mass of the epidermis and hair follicle epithelium, which obscured the dermoepidermal junction. Neoplastic cells were immunopositive for S100, PNL-2, vimentin and melan-A antigens. No immunolabelling of CD3, CD79, Iba-1 or pancytokeratin was observed. This is the first detailed description of spontaneous amelanotic malignant melanoma in this species. [ABSTRACT FROM AUTHOR]

Malignant melanomas tend to be locally destructive, aggressive tumours commonly associated with recurrence and/or metastasis. In this report, a 13-year-old captive white African lioness (Panthera leo), with a recent history of intermittent bouts of lethargy and inappetence, presented with a distended abdomen (due to ascites) and a small, round crusty lesion on the ear. An abdominal ultrasound showed the presence of masses on the liver and an exploratory laparotomy revealed multiple pale lesions on the liver and omentum. Histopathology revealed sheets of pleomorphic neoplastic cells compressing the non-neoplastic liver tissue. Similar neoplastic cells had multifocally expanded and effaced omentum adipose tissue, as well as formed a well-circumscribed mass in the ear sample, extending from close to the epidermis to the lateral and deep margins of the section. All three tissue samples had a high mitotic index (15 per 10 HPF), and critically, in the ear sample, there were rafts of neoplastic cells in the lymphatics, indicating lymphovascular invasion. Immunohistochemistry for the melanoma marker, PNL-2, showed strong positivity in all three tissue samples. Thus, the diagnosis was of malignant melanoma with metastasis to the liver and omentum. This is the first report of metastatic cutaneous melanoma in a lion.

Chromatophoromas are neoplasms arising from pigment-bearing cells (chromatophores) of the dermis. While isolated cases have been reported in the literature, the prevalence and biological behavior of chromatophoromas in snakes are unknown. Forty-two chromatophoromas were identified among 4663 submissions (0.9%) to a private diagnostic laboratory in a 16-year period. The most commonly affected snakes were colubrids (23 cases, 55%) and vipers (8 cases, 19%). The San Francisco garter snake was the most commonly affected species (6 cases; 14% of all affected snake species and 3.7% of all garter snake submissions). No sex predilection was found. The age of 28 snakes ranged from 5 to 27 years. Single cutaneous chromatophoromas were most commonly observed and presented as pigmented cutaneous masses or plaques along any body segment. Euthanasia or death due to progressive neoplastic disease or metastasis was reported in 8 (19%) and 4 (10%) cases, respectively. The survival time of 4 animals ranged from 4 to 36 months. Microscopically, xanthophoromas, iridophoromas, melanocytic neoplasms, and mixed chromatophoromas were identified, with melanocytic neoplasms being most common. Microscopic examination alone was generally sufficient for the diagnosis of chromatophoroma, but immunohistochemistry for S-100 and PNL-2 may be helpful for diagnosing poorly pigmented cases. Moderate to marked nuclear atypia appears to be consistently present in cutaneous chromatophoromas with a high risk of metastasis, while mitotic count, lymphatic invasion, the level of infiltration, and the degree of pigmentation or ulceration were not reliable predictors of metastasis. [ABSTRACT FROM AUTHOR]