Case Report of a Mare Diagnosed with a Metastatic Mammary Carcinoma after the Excision of a Recurrent Intraocular Neuroepithelial Tumor

SIMPLE SUMMARY: This case report describes the unusual presentation of two rare tumors in a mare diagnosed over a short period of time (9 months), affecting the eye and the mammary gland, with a relapse of the ocular tumor presenting histological features that cannot be attributed to any specific neoplastic entity. In the study, we describe the in vivo diagnosis and treatment of the neuroepithelial intraocular tumor and the post mortem detection of a metastatic malignant mammary carcinoma. ABSTRACT: A 24-year-old Irish Cob mare was presented with a peripheral iris mass, which was surgically resected and diagnosed as an undifferentiated neuroepithelial tumor. A few months later, a relapse occurred with histological features characterized by a more solid appearance and squamous differentiation. Subsequently, the mare was presented with rapidly spreading multiple subcutaneous masses and, at the onset of neurological signs, was humanely euthanized and subjected to a complete post mortem examination. The necropsy confirmed the presence of numerous widespread masses in the subcutaneous tissue, several internal organs, and mammary gland. Histological and immunohistochemical (IHC) examinations were performed on all masses, allowing the diagnosis of mammary carcinoma with several visceral and subcutaneous metastases. Considering the post mortem findings, the second intraocular mass was submitted to histological and IHC re-evaluation to differentiate it from an intraocular metastasis of the mammary carcinoma. The results of the histological and IHC analyses confirmed the diagnosis of neuroepithelial tumor relapse. This is the first case of a metastatic mammary carcinoma concurrent with a recurrent intraocular neuroepithelial tumor in a mare. This case was a challenge for both clinicians and pathologists involved and highlighted the importance of post mortem and IHC evaluations.