Oxidative stress and immunomarkers in equine dermal melanomatosis: single-case comparison with healthy individual.

Dermal melanomatosis is a common tumor in grey horses, characterized by cutaneous/subcutaneous lesions with metastatic potential. While clinically well-described, oxidative stress involvement remains poorly understood. This case report compared oxidative stress markers and antioxidant enzymes' activities in total protein extracts from melanomatosis lesions (grey horse) versus healthy control skin (black horse), alongside histopathology and immunohistochemistry, to correlate oxidative imbalance and tumor behavior. Melanomatosis tissue exhibited decreased antioxidant defenses confirmed by catalase (CAT) and superoxide dismutase (SOD) reduced activities, with 29% lower glutathione (GSH) levels. Oxidative damage markers increased in melanomatosis tissue: malondialdehyde (MDA) rising by 73% and advanced oxidation protein products (AOPP) by 56%. Histology confirmed melanocytic proliferation, supported by moderate positive S100 (highly sensitive melanocytic marker) and low proliferation rate (8% positive to proliferation marker Ki-67). These findings suggest oxidative stress was involved in melanomatosis pathophysiology in this case, highlighting the potential relevance of these markers for further investigation.