Mammary carcinoma with ocular metastasis in a mare

Mammary neoplasias in mares are considered a rare event, usually documented via case reports [1,2,3] or in small case series [4], with a carcinoma prevalence rate of 0,11% [3]. An endo-ocular mass from a 24 years old nonpregnant sella italiano mare was conservatively removed and istologically and immunohistochemically diagnosed as a neuroepithelial benign tumor (adenoma of the ciliary body). A second eye mass was then surgically excised with a second histological outcome consistent with a solid carcinoma with squamous differentiation. Due to poor clinical conditions, the animal was euthanized and sent to the necropsy service of the Department of Comparative Biomedicine and Food Science. Necropsy findings showed a primary solid firm mass with a diameter of 15 cm, involving the right mammary gland, with a yellow-whitish cut surface with a central portion of necrosis. One to 6 cm in size, similar nodular masses were found in several tissues and organs including skin, lungs, lymph nodes at different sites, heart, liver, pancreas, parotid gland, intestinal wall (rectum and colon), adrenal glands, muscles and brain. Samples for histological and immunohistochemical examination were collected and routinely processed from all the grossly affected tissues. H&E sections from the primary mass showed multifocal necrosis and a primary neoplastic population of closely packed malignant epithelial cells organized in solid sheets, with foci of squamous differentiation and occasional tubule formation, admixed in abundant fibrovascular stroma and associated with a second population of benign myoepithelial cells. The latter were not detectable in most of the metastases analyzed. Selected sections of the primary tumors and metastases were then immunohistochemically stained for panCK, CK14, CK5-6, CK8-18, vimentin, p63 and calponin (avidin-biotin complex method with a BenchMark automatic immunostainer). As positive control, a dog mammary gland comprehensive of healthy skin and mammary gland was used. The antibody-panel showed: i) strong or mild positive staining in both the primary tumor and metastases for panCK (showing epithelial differentiation) and CK5-6 and CK14, consistent with a proliferation either of basal epithelial cells or myoepithelial cells; ii) occasional positivity for vimentin and p63, and positivity only in the metastases for calponin, consistent with a mild and focal myoepithelial proliferation; iii) inconsistent results for CK8-18, consistent with a low or insignificant proliferation of the luminal epithelium. The findings are compatible with an infiltrative solid carcinoma associated with hyperplasia of the myoepithelial cells. Our findings suggest that the second endo-ocular mass clinically detected was not a relapse of the adenoma of the ciliary body, but a metastasis of the undiagnosed mammary tumor. Despite the reported tendency to metastasize to multiple organs [1,2,4], this is (at the best of our knowledge) the first confirmed ocular metastasis of a mammary carcinoma in a mare