An animal model for human melanoma

Malignant skin neoplasms in goats in Sicily, Italy: clinical, virological and pathological investigations

Neoplasms in small ruminants are considered uncommon and their reported incidence is variable. The aims of this investigation were to characterize malignant skin neoplasms in adult goats reared in Sicily, Italy, and to evaluate potential correlations between gross and histopathology features of the tumours and signalment, tumour location and/or viral infections. A total of 75 malignant skin masses were examined. In selected animals with perineal masses (n = 28) virological and serological investigations on tissues and blood were also conducted. According to the histological features, the lesions were classified as 67 squamous cell carcinomas (SCCs) (of which 65 were located in the perineum), six melanomas and two fibrosarcomas. In three cases, neoplasms at the base of the horn were associated with nasal polyps. Among the selected perineal SCCs, papillomaviruses (PVs), caprine herpesvirus 1 and parapoxvirus were not detected on polymerase chain reaction or on serological examination. However, further investigation on a larger sample size is required to evaluate the potential role of PVs in the pathogenesis of skin tumours in goats.

Research Relevant Background Lesions and Conditions: Ferrets, Dogs, Swine, Sheep, and Goats

Animal models provide a valuable tool and resource for biomedical researchers as they investigate biological processes, disease pathogenesis, novel therapies, and toxicologic studies. Interpretation of animal model data requires knowledge not only of the processes/diseases being studied but also awareness of spontaneous conditions and background lesions in the model that can influence or even confound the study results. Species, breed/stock, sex, age, anatomy, physiology, diseases (noninfectious and infectious), and neoplastic processes are model features that can impact the results as well as study interpretation. Here, we review these features in several common laboratory animal species, including ferret, dog (beagle), pig, sheep, and goats.

One hundred two tumors in 100 goats (1987-2011)

Of 1146 caprine necropsy or biopsy specimens submitted from 1987 through 2011 to the Veterinary Diagnostic Laboratory at Oregon State University, 100 goats (8.7%) had 102 tumors. Detailed records were available for 89 cases. Fifty-five goats were female, 17 were castrated males, and 12 were intact males. Breeds included 21 Nubian, 16 Pygmy, 10 Pygora, 8 Alpine, 4 Angora, 4 Saanen, 2 Toggenburg, and 9 crossbred goats. Dwarf, Nubian, and Saanen goats were overrepresented and Alpine and Boer goats underrepresented among cases with neoplastic disease in comparison to submissions overall. Age ranged from 7 months to 19 years (median, 7 years). Histopathology was performed on 97 tumors. Lymphoma (n = 17) was the most common tumor, followed by cutaneous squamous cell carcinoma (n = 10) and thymoma (n = 9). Most lymphomas were multicentric. All 7 mammary neoplasms were adenocarcinomas. Five of 7 vascular proliferations were hemangiosarcomas. All 4 melanocytic tumors were classified as (malignant) melanoma. Rarely reported caprine tumors included a choroid plexus carcinoma, 2 rhabdomyosarcomas, and 3 pheochromocytomas. Cutaneous round cell tumors were provisionally diagnosed as 2 histiocytomas and 5 mast cell tumors. Single cases of previously unreported caprine tumors included amyloid-producing odontogenic tumor, myxosarcoma, sebaceous carcinoma, apocrine sweat gland adenoma, and thyroid carcinoma. Nonneoplastic entities included 2 cases of mammary fibroadenomatous hyperplasia and single cases of vascular hamartoma, cervical adenomatous hyperplasia, and cervical leiomyofibromatosis. The results of this 25-year retrospective study indicate that lymphoma in particular and tumors in general are common in goats.

Immunohistochemical characterization of perineal melanoma in Kilis goats

We describe the clinical, histopathological and immunohistochemical features of the malignant melanomas in the perineal regions of Kilis goats from Sanliurfa province in Turkey. We studied 13 female Kilis goats between 3 and 8 years old that were brought to Harran University Veterinary School, Department of Surgery, between 2002 and 2010. By macroscopic examination, the masses were determined to have elastic consistency, dark brown-black color, necrotic surfaces and ulceration. Microscopically, pleomorphic cells were observed under the basal layer and these advanced toward the dermis. These cells were polyhedral, round or spindle-shaped, anaplastic, and their cytoplasm contained varying amounts of dark brown-black pigments. Immunohistochemical staining was obtained with anti-melan A, vimentin and S100 antibodies.

Melanocytic tumour in a black sheep never exposed to ultraviolet radiation

A slow growing skin tumour was identified on the head of a 6-year-old male Serra da Estrela black sheep. The animal had no previous history of exposure to ultraviolet radiation or illness. The tumour consisted of an irregular mass subdivided into two polypoid regions and there were small alternating pigmented and non-pigmented areas in the surrounding epidermis. Microscopical and immunohistochemical features were consistent with a melanocytic tumour of the melanocytoma type, without signs of vascular or perineural invasion. The tumour cells contained pigment stained by the Masson Fontana reaction, expressed S100 protein and vimentin and displayed a low proliferative rate (Ki67 labelling <1%). No metastases were found at the time of gross necropsy examination. Analyses of the homologous regions of the hot spot mutational exons of BRAF and NRAS (the genes that are most often mutated in human melanocytic tumours) did not reveal alterations, but there were silent polymorphic variations in these genes. No such variation was observed in the GNAQ gene sequence that is mutated in human melanocytomas.

Malignant melanoma of the horn base in a Pygora goat

A case of malignant melanoma, originating at the base of the left horn, was diagnosed in a white 11-year-old Pygora doe. At necropsy, the goat had an ulcerated, black-pigmented, 2.5-cm mass at the base of the left horn. Firm masses diffusely black on the cut surface were present at the left horn base, subcutaneously over the frontal bones, and infiltrating into the frontal sinuses, the submandibular lymph node, and left parotid salivary gland. The left maxillary premolars and molars were loosened from the periodontia. Multiple black foci of metastasis were observed in the liver. Histologically, the masses consisted predominantly of moderately pleomorphic, polyhedral to spindle cells that contained variable amounts of dark brown intracytoplasmic pigment granules. The tumor cells were positive for Melan A by immunohistochemical staining.

A comparative review of melanocytic neoplasms

Melanoma is a devastating disease frequently encountered within both veterinary and human medicine. Molecular changes linked with neoplastic transformation of melanocytes include mutations in genes that encode proteins intrinsic to the regulatory pathways of two tumor suppressor proteins (retinoblastoma protein and p53), proto-oncogene mutation to oncogenes, altered expression of epithelial cadherin and CD44 adhesion molecules, and upregulation of angiogenic factors and other growth factors. Histologic evaluation of the primary mass is the most common means of diagnosis, with cytology used more frequently to document metastasis. Melanoma's highly variable histologic and cytologic patterns can make diagnosis by either method problematic. Adherent epithelioid morphology, including signet ring forms, and nonadherent round and spindle forms are recognized, with pigmentation an inconsistent finding. The site of the tumor, the thickness of the primary tumor or depth of invasion, and the number of mitotic figures per high-power field or per millimeter are used histologically to predict biologic behavior, whereas site and degree of pleomorphism are typically used for cytologic preparations. Diagnosis of amelanotic melanoma can be aided by ancillary diagnostic techniques. Tumor cells are usually positive for vimentin, S100, neuron-specific enolase, and Melan-A, and negative for cytokeratin. Melan-A as a positive marker is not as sensitive as the others are but is likely more specific. Monoclonal antibodies to human melanosome-specific antigens 1 and 5 cross-react with canine antigens for a combined sensitivity rate of 83%. Mouse monoclonal antibody IBF9 specifically recognizes canine melanoma antigen and also has good sensitivity. Serologic markers, including cytokines, cell adhesion molecules, and melanoma-inhibitory activity, are being investigated as potential sentinels of melanoma. Currently, there is no single diagnostic technique capable of differentiating benign from malignant melanocytic neoplasms or predicting survival time.

Photobiology and genetics of malignant melanoma

The current state of knowledge of melanoma genetics is reviewed. Mutations in the tumour suppressor gene CDKN2A and in the oncogenes N-ras and H-ras seem to play the most important roles in the development and progression of malignant melanoma. Experimental studies to determine the role of ultraviolet (UV) light in the induction of melanoma have been hampered by a lack of suitable animal models. The commonly used laboratory animals are not susceptible to the induction of melanoma upon exposure to UV radiation (UVR) alone. Recent observations with four different animals have suggested, however, that UVR may be involved in the induction of melanoma. The most recent model consists of human skin grafted onto immunodeficient mice. To date, using this model, only the combination of UVB (280-320 nm) exposure and topical promoter treatment has led to the development of malignant melanoma. The wavelength dependency of the induction of melanoma has been established in the fish model Xiphophorus. The application of such an action spectrum to humans looks possible.