LYMPHOID NEOPLASIA IN THE KOALA (PHASCOLARCTOS-CINEREUS) - A REVIEW AND CLASSIFICATION OF 31 CASES

Lymphoid neoplasia is the most common form of neoplasia in the koala ( Phascolarctos cinereus), but limited clinical, hematologic, and bioche mical data have been recorded for this condition. A clinicopathologic survey was performed on 31 koalas with lymphoid neoplasia. Tumors were classified on the basis of anatomic distribution at necropsy, with th e majority (18) being multicentric. Organs commonly affected by the mu lticentric type included superficial lymph nodes (always involved), li ver, spleen, and bone marrow. Alimentary lymphosarcoma (six), primary lymphoid leukemia (three), and miscellaneous forms (four) were also fo und. Lymphoid neoplasia was most common in middle-aged animals, with n o sex predilection. At presentation, body condition ranged from very p oor to good, suggesting variability in either intensity of disease or duration of illness. Animals were often listless and appeared to have muscular weakness. Lymphadenomegaly was not always determined clinical ly in cases of multicentric lymphosarcoma. Abdominal pain was present in three of the six animals with alimentary lymphosarcoma. Concurrent disease was detected in six of the 31 animals. Based on blood smears o r bone marrow aspirates of 15 leukemic animals (and supported by histo logic examination), seven koalas in three anatomic categories had neop lastic cells with small to medium noncleaved nuclei. Four koalas had n eoplastic cells with large cleaved nuclei. Fourteen of 14 koalas analy zed with multicentric forms were leukemic, as were three of three with primary lymphoid leukemia, although none of the four with alimentary lymphosarcoma that were analyzed were leukemic. Anemia was present in 14 of 22 koalas analyzed and across all anatomic categories. In 18 ani mals analyzed biochemically, hypoalbuminemia was detected in 12, incre ased lactate dehydrogenase in eight, and azotemia in eight. There was no correlation with a particular anatomic group. Cytologic or histolog ic examination of bone marrow confirmed all cases of primary lymphoid leukemia and detected secondary leukemia associated with the other ana tomic forms. The anatomic classification used for lymphoid neoplasia i n domestic animals appears to have applicability to the koala. However , further delineation will require examination of additional animals a nd correlation with immunophenotyping.