Disseminated histiocytic sarcoma in 2 FeLV-positive cats in Brazil.

Histiocytic sarcomas (HSs) are uncommon malignant neoplasms in cats, typically affecting older animals and not previously associated with feline leukemia virus (FeLV). Here, we describe 2 cases of disseminated HS in young FeLV-positive domestic shorthair cats that clinically and grossly mimicked lymphoma. Case 1, a 1-y-old female cat, was presented with hemiplegia and dysuria and was euthanized because of the clinical suspicion of spinal lymphoma. Case 2, a 4-y-old male cat, had hyporexia, ocular abnormalities, and bilateral renal enlargement and was euthanized because of the clinical suspicion of renal and ocular lymphoma. Both cases tested positive for feline leukemia virus (FeLV) infection with a SNAP test. At autopsy, case 1 had a white, irregular, intradural spinal cord mass at the C6-C7 segment, and case 2 had coalescing, unencapsulated, white nodules that effaced both renal cortices, along with uveal thickening in the left eye with hyphema. Both cases had highly pleomorphic neoplastic round-cell proliferation in neoplastic masses, with strong cytoplasmic labeling for vimentin and IBA1 on immunohistochemistry and no CD20 or CD3 labeling, confirming disseminated HS. The neoplastic cells also had strong cytoplasmic immunolabeling for FeLV, suggesting a possible oncogenic role of FeLV in feline HSs.