Disseminated melanoma in a dog with involvement of leptomeninges and bone marrow

Case report: MRI and CT imaging features of a melanocytic tumour affecting a cervical vertebra in an adult dog, and review of differential diagnosis for T1W-hyperintense lesions

A 7-year-old Lhasa Apso presented with a history of left thoracic limb lameness and neck pain. Magnetic resonance imaging revealed a well-defined, extradural lesion that was hyperintense on T1-weighted (T1W) images and isointense on T2-weighted (T2W) images and T2* images located at the left lamina of the C4 vertebra. Computed tomography showed an isoattenuating and contrast-enhancing mass centered on the left C4 vertebral lamina with associated osteolysis. The mass was surgically debulked, and histopathology revealed a malignant melanocytic tumour. The patient recovered completely and received radiotherapy and three doses of the melanoma vaccine as adjunctive treatment. Eighteen months following treatment, the patient presented with neck pain again, but further investigations were declined at this stage, and the patient was euthanised. To the author's knowledge, this is the first case report describing the imaging characteristics of a cervical extradural melanocytic tumour in a dog. This case illustrates the MRI and CT imaging features and treatment of a canine melanocytic tumour of the cervical vertebrae.

Unusual Canine Cutaneous Melanoma Presenting Parietal Bone Metastasis: A Case Report

Melanocytic tumour anatomic location is considered an important prognostic indicator. The cutaneous forms are generally considered benign and may show various biological behaviours. This work reports a rare case of canine cutaneous melanoma showing parietal bone metastasis. Bone invasion in melanocytic tumours is often described in oral or visceral melanomas, but not in cutaneous forms. The patient (dog, male, mixed breed, 12 years) was initially presented for the surgical removal of a cutaneous tumour located on the skin of the carpal region of the right forelimb. Four months after, the patient returned with enlarged lymph nodes and acute respiratory failure. The patient was euthanized due to a decline in physical condition. The necropsy showed metastases in the affected forelimb, regional lymph node, splanchnic organs, parietal bone and meninges. Histopathological examination of tumour tissue samples revealed a mixture of pigmented and non-pigmented spindle and epithelioid melanocytes, while according to immunohistochemistry, the tumours showed a strong immunopositivity for VEGF and MMP-10, and a moderate positivity for MMP-2 expression. This case shows that cutaneous melanocytic tumours may show an aggressive malignant form with positive immunohistochemical reactions for multiple invasiveness factors.

A case of malignant melanoma, a possible primary site in the digit, with systemic metastasis in a mini-Rex

We report a case of systemic metastasis of malignant melanoma in a mini-Rex (Oryctolagus cuniculus). The animal presented with lameness of the right hind limb, swelling of popliteal lymph node, and a black mass on the first digit. Paralysis of hindlimbs and forelimbs, dysuria, and dysphagia progressed over time, and the rabbit died on day 35 from the first visit. At necropsy, many black lesions were observed in multiple organs including the marrow of most bones. Histopathologically, the tumor cells had highly atypical nuclei of various sizes and an abundant eosinophilic cytoplasm, and some cells contained melanin granules. These cells were positive for PNL2 and S-100, melanoma markers, by immunohistochemistry. This is the first report of malignant melanoma in a mini-Rex with severe malignancy and systemic metastasis including the bone marrow.

Diagnosis of meningeal melanomatosis in a dog using magnetic resonance imaging and cerebrospinal fluid findings

A 13-year-old spayed female Labrador Retriever was presented with severe progressive tetraparesis. The neuroanatomic localization was the C1-C5 spinal cord segments with brainstem or cranial nerve involvement. Magnetic resonance imaging revealed diffuse T1-weighted and T2-weighted hyperintense lesions with strong contrast enhancement spreading through meninges of the cervical spinal cord and the brain. Few small round areas showing T1-weighted hyperintensity and T2-weighted hypointensity were scattered within the lesions. Cerebrospinal fluid analysis revealed neoplastic round cells and possible melanocytes. Malignant melanoma was suspected. At necropsy, the brain and the entire spinal cord were covered with thick, dark membranous tissue. Based on histopathologic findings, a positive response against Melan-A, and no melanoma identified outside the central nervous system, primary meningeal melanomatosis was diagnosed.

Spontaneously occurring melanoma in animals and their relevance to human melanoma

In contrast to other cancer types, melanoma incidence has been increasing over the last 50 years, and while it still represents less than 5% of all cutaneous malignancies, melanoma accounts for the majority of skin cancer deaths, due to its propensity to metastasise. Whilst melanoma most commonly affects the skin, it can also arise in mucosal surfaces, the eye, and the brain. For new therapies to be developed, a better understanding of the genetic landscape, signalling pathways, and tumour–microenvironmental interactions is needed. This is where animal models are of critical importance. The mouse is the foremost used model of human melanoma. Arguably this is due to its plethora of benefits as a laboratory animal; however, it is important to note that unlike humans, melanocytes are not present at the dermal–epidermal junction in mice and mice do not develop melanoma without genetic manipulation. In contrast, there are numerous reports of animals that spontaneously develop melanoma, ranging from sharks and parrots to hippos and monkeys. In addition, several domesticated and laboratory‐bred animals spontaneously develop melanoma or UV‐induced melanoma, specifically, fish, opossums, pigs, horses, cats, and dogs. In this review, we look at spontaneously occurring animal ‘models’ of melanoma and discuss their relevance to the different types of melanoma found in humans. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland..

Pathological features of 78 metastatic or multicentric neoplasms involving the central nervous system in dogs

ABSTRACT: Secondary neoplasms affecting the central nervous system (CNS) may occur through blood flow or direct extension. This condition occurrence has increased both due to a longer life expectancy of dogs, as well as with the employment of chemotherapeutics, which may increase the survival period and, thus, the odds of the occurrence of metastasis. The aim of this study was to analyze the epidemiological features, such as the age, breed and sex of the animals affected, as well as the gross and microscopic findings of the metastasis from neoplasms involving the CNS of 78 dogs, and, based on the data, estimate the occurrence and frequency of the metastatic or multicentric neoplasms. Females (71.79%) were most affected than males, with an average age of 9.5-years-old and a median of 10-years-old. Most of the cases had a multifocal distribution (73.07%), and epithelial neoplasms (50%) were the most common. Telencephalon was the most affected neuroanatomical region (61.1%). Mammary neoplasms were the most frequent (47.44%), followed by hemangiosarcoma (19.23%), lymphoma (10.26%) and melanoma (6.41%). Less common neoplasms included osteosarcoma, histiocytic sarcoma and lung carcinoma (2.56%). Mammary neoplasms were mainly composed of anaplastic and micropapillary carcinomas, of which only multifocal microscopic lesions were observed.

Amelanotic melanoma in a New Zealand White Rabbit (Oryctolagus cuniculus)

A 3.5-year-old intact male double-transgenic New Zealand white rabbit (Oryctolagus cuniculus), apoA-I and LCAT (apolipoprotein and lecithin:cholesterol acyltransferase), was presented with a discrete, raised facial mass (0.5 x 1.0 x 1.0 cm). The mass was surgically excised, with reoccurrence to the same site 88 days later. A second surgical excision was performed, and the rabbit died 3 weeks later from respiratory distress. At necropsy, multiple varying-sized masses were observed in the ventral mandibular region and throughout the lungs, pleura, and diaphragm. On histopathology, the masses were composed of moderately anisocytotic and anisokaryotic polygonal to spindloid cells with moderate finely granular, lightly eosinophilic cytoplasm, having round to oval nuclei with one to several nucleoli and finely stippled chromatin. Mitotic figures were frequent. Lymphatic and venous invasion were noted with neoplastic cells metastasized to the submandibular lymph nodes, lungs, liver, and adventitial surface of the aorta. Fontana-Masson stain was negative for melanin, thereby necessitating immunohistochemistry and transmission electron microscopy. Positive staining with MART-1 (a melanocyte protein marker) combined with transmission electron microscopy revealing type II melanosomes confirmed the diagnosis of an amelanotic melanoma.