T-cell lymphoma in a Himalayan black bear in China.

A 12-y-old Himalayan black bear suddenly developed depression, anorexia, cough, and dyspnea and died at the Ordos Zoo, China. At autopsy, the mesenteric and cranial mediastinal lymph nodes (LNs) were enlarged; the largest cranial mediastinal LN was ~13 cm in diameter. Scattered-to-diffuse, rounded-or-oval, gray, firm 1-6-mm nodules were observed on the surfaces of the spleen, liver, lungs, and small intestine. Histologically, the enlarged cranial mediastinal and mesenteric LNs, spleen, small intestine, lungs, and liver contained dense populations of neoplastic lymphoid cells (NLCs). The NLCs were round-or-oval with small amounts of mildly eosinophilic cytoplasm and round-or-oval hyperchromatic nuclei with indistinct nucleoli; the mitotic count was 55 in 2.37 mm2. Immunohistochemically, cell membranes and the cytoplasm of NLCs were CD3+, CD79a-, CD20-, CD15-, CD30-, and CD45RA-; hence, the NLCs were derived from T lymphocytes. To our knowledge, T-cell lymphoma has not been reported previously in a Himalayan black bear.