Malignant B-cell lymphoma with Mott cell differentiation in a ferret (Mustela putorius furo).

A 3.5-year-old, male, neutered ferret (Mustela putorius furo) was presented with a 3-day history of lethargy and anorexia. Splenic aspirates revealed high numbers of intermediate-sized lymphocytes and Mott cells interpreted as lymphoma with Mott cells. The ferret was euthanized because of a poor clinical prognosis. Postmortem examination revealed markedly enlarged spleen and lymph nodes, with multifocal white nodules in the liver parenchyma. Histologically, the spleen had multifocal large nodules composed of neoplastic lymphocytes with frequent Mott cells. Similar neoplastic cells were present in the sections of liver, lymph nodes, and bone marrow. These cells were cluster of differentiation (CD)3-negative, CD79alpha-positive, and lambda light-chain-positive. Electron microscopy revealed that the cytoplasm of the neoplastic Mott cells had increased, disorganized, dilated, rough endoplasmic reticulum containing electron-dense immunoglobulin. On the basis of cytologic, histopathologic, immunohistochemical, and electron microscopic findings, a malignant B-cell lymphoma with Mott cell differentiation was diagnosed.