Cutaneous melanocytomas in a cow

Objectives: To describe the clinical and histopathological aspects of a cutaneous melanocytoma observed in a 3 and half-year old Holstein cow. Methods: The surgical extirpation of the tumor was performed directly at the farm. The cow was restrained in standing and a paravertebral anaesthesia with 2% Lidocaine was performed. An infiltrative subcutaneous anaesthesia was additionally performed around the pedunculous of the neoplasia. The neoplasm was totally extirpated; ligature of blood vessels was necessary to prevent excessive bleeding. Representative samples from the mass were collected, fixed in 10% buffered formalin, embedded in paraffin, and routinely processed for histologic examination. Five micron sections were stained with haematoxylin and eosin. The postoperative follow up lasted one month: the cow had no further problems and the site of surgery healed as expected. Results: The extirpated tumour was a 32 x 32 x 16 cm pedunculated and irregularly rounded mass, covered by dark, thick skin, that protruded from the right lateral/dorsal region. The total weight of the mass was 10.5 kg. Cut section of the neoplasm was bright and blackish and it had a compact consistency with scattered areas of fine white streaks. The sections stained with haematoxylin and eosin revealed a normal epidermis with focal slight hyperkeratosis while in the dermis, within an extensive, dense an pinkish collagenous matrix, there were many rounded to polygonal cells, sometimes fusiform, full of dark-brownish and granular pigments (melanin) within the cytoplasm and poorly visible nuclei. The cells were often arranged around small blood vessels. In other fields it was possible to observe elongated and fusiform cell, arranged in whorls. Numerous cells of other fields showed totally lack of melanin granules. Anisocytosis and anisokaryosis were moderate. Mitotic activity was low with 1 mitosis per 10 high-power fields. On the basis of these findings diagnosis was coherent with a benign dermal melanocytoma, a rare form in cattle, arising from the dermal melanocytes. Conclusions: The term melanocytoma encompasses the benign forms of melanocytic neoplasms, whereas the term melanoma is used for the malignant forms. However, the literatures clearly emphasizes the difficulties in definitely differentiating the benign from the malignant forms. With this in mind, the described tumour was considered benign on the base of the following findings: no other metastatic masses were clinically founded, the extirpated tumour did not infiltrate the upper epidermis and surrounding tissues, mitotic activity was very low and there was no evidence of lymphovascular invasion. This is also in accordance with literature that indicates that the majority of melanocytic neoplasms in cattle are benign in nature. Despite the fact that such kind of neoplasia are quite rare in cattle, more investigation may be worth of being carried out, eventually as model for human medicine.