Primary sinonasal malignant melanoma with systemic metastasis in a non-gray horse.

This research article details the case of a 27-year-old Anglo-Arabian horse with a malignant melanoma tumor in its left maxillary sinus, which also metastasized to other parts of its body. This is notable due to the rarity of this type of tumor in horses, and the fact that the horse did not possess the genetic “gray” factor commonly associated with such tumors in this species.

Research Details and Findings

• The study centred on a 27-year-old Anglo-Arabian gelding that had presented with swelling in the left maxillary region. The exploration of this unusual swelling led to the discovery of a black-red tissue filling the left maxillary sinus.
• A biopsy of the abnormal tissue was conducted and led to the diagnosis of malignant melanoma, a type of highly aggressive cancer in horses.
• DNA testing was undertaken to detect a genetic predisposition to melanomas. The researchers focused on the gene responsible for gray coat color, known to be correlated with such cancers, but found that this horse did not carry this factor. This was a significant finding, as the horse did not possess the genetic trait commonly linked to this type of cancer.
• Unfortunately, despite the intervention and research undertaken, the condition of the horse deteriorated and it was euthanized approximately three months after diagnosis. An autopsy showed that the cancer had spread from the original site to other organs in the body, including the lymph nodes, spleen, liver, kidney, and adrenal glands. However, no tumors were found in the skin or pelvic regions.
• The pathology of the metastasized tumors was identical to that of the original tumor in the maxillary sinus, confirming they were all malignant melanomas. Importantly, this included the discovery of tumor emboli in the kidney.

Implications and Conclusions

• The case highlights sinonasal mucosal melanoma as a rare but serious disease in horses. It’s importance lies not only in its rarity but also in the discovery that this specific horse did not carry the “gray” gene factor, generally considered a predisposing trait for melanomas in horses. This raises questions about possible different etiological factors involved in the development of such cancers in non-gray horses.
• Furthermore, the autopsy officials observed that the tumor spread aggressively throughout the body, suggesting that this form of cancer can be particularly invasive and fast-spreading, increasing the urgency for early detection and intervention.
• In conclusion, the findings of this case report suggest that more research is needed into the causes and progression of sinonasal mucosal melanoma in horses, particularly those that do not possess the typical genetic markers linked to this form of cancer.