Evaluation of ERG as a biomarker for immunohistochemical diagnosis of canine splenic hemangiosarcoma.

Hemangiosarcomas (HSAs), aggressive malignant neoplasms originating from endothelial cells lining blood vessels, are the most common splenic tumors in dogs. Immunohistochemical diagnosis of HSAs currently relies on endothelial markers such as CD31, which, while useful, have suboptimal sensitivity and specificity. In human pathology, E-26 transformation specific-related gene (ERG), a nuclear transcription factor expressed in endothelial cells, has demonstrated high diagnostic performance for vascular tumors. Therefore, this study aimed to evaluate the diagnostic utility of a human-specific anti-ERG antibody in canine splenic vascular tumors. Performance of this antibody was evaluated in three groups of canine splenic tumors: 64 benign and malignant blood vascular tumors (to assess sensitivity) and 117 stromal tumors and 10 hematopoietic or metastatic epithelial tumors (to assess specificity) and compared to that of CD31 in group one and three. All 64 blood vascular tumors (both benign and malignant) were ERG-positive, yielding a sensitivity of 100%, whereas only 87% of these tumors were CD31-positive. Among the 116 evaluable stromal tumors, 112 (97%) were ERG-negative, confirming their non-vascular origin. Four cases showed ERG expression, two of which were also CD31-positive and were subsequently reclassified as HSAs. ERG expression was variable in the hematopoietic and metastatic epithelial tumors. In conclusion, the anti-ERG antibody demonstrated superior sensitivity and comparable specificity to CD31 for diagnosing canine splenic vascular tumors. These findings support the use of ERG as a reliable immunohistochemical marker in veterinary pathology for the diagnosis of vascular tumors in dogs.