Association Between Matrix Metalloproteinase-9 (MMP-9) Immunohistochemical Expression and Clinicopathological Features in Equine Melanoma.

BACKGROUND

Equine melanoma is one of the most important oncological diseases in horses and exhibits a distinct biological behavior compared with melanoma in other species. Matrix metalloproteinase-9 (MMP-9) has been associated with tumor aggressiveness and metastasis in human and canine melanoma, but its expression in equine melanoma remains unknown.

AIMS/

OBJECTIVES

Evaluate the immunohistochemical expression of MMP-9 in equine melanomas and investigate its association with clinicopathological features.

METHODS

68 formalin-fixed, paraffin-embedded equine melanomas from 48 gray horses were evaluated immunohistochemically for MMP-9 expression. Associations between MMP-9 expression and clinicopathological variables were assessed, including histological classification, tumor size, excision interval, ulceration, circumscription, tumor localization, and stromal immunolabeling. Statistical significance was considered when p < 0.05.

RESULTS

Overall, 69.1% of melanomas exhibited low MMP-9 expression, 27.9% high expression, and 2.9% were negative. Malignant melanomas exhibited significantly higher MMP-9 expression than benign tumors (p = 0.04). Medium-sized tumors showed significantly higher MMP-9 expression than small tumors (p = 0.02). MMP-9 immunolabeling was positively correlated with excision interval (p = 0.03), and longer excision intervals were associated with histological malignancy (p < 0.001). No significant associations were identified between MMP-9 expression and ulceration, tumor circumscription, horse age, tumor localization, or number of tumors.

CONCLUSION

This study provides the first immunohistochemical characterization of MMP-9 expression in equine melanoma. MMP-9 expression was predominantly low, but was significantly associated with histological malignancy, medium tumor size, and longer excision intervals. These findings may help to expand the current clinicopathological characterization of equine melanoma.