Lymphoid neoplasia in the koala

Objective Correlation of immunophenotype with history, anatomical and morphological features of lymphoid neoplasia in the koala. Methods Routine necropsies were performed on 51 koalas with suspected lymphoid neoplasia between 1986 and 1997 in New South Wales and Queensland. Immuno‐phenotyping was by an immunoperoxidase method utilising species cross‐reactive antibodies raised against human lymphocytes and an antibody raised against koala IgG. Cases were classified according to organs and tissues affected and the morphological features of neoplastic cells. Results Twenty‐six (51%) of the cases were of the T cell immunophenotype, 12 (24%) were of B cell immunopheno‐type and 13 (25%) did not stain. The age and sex of koalas did not correlate with immunophenotype (P = 0.686 and P = 1.000, respectively). Thirty‐two cases were leukaemic and 36 had multiple organ involvement, probably reflecting presenta tion of koalas at advanced stages of disease. Abdominal tissue involvement was most common (44 cases), followed by nodal (32), atypical (21) and cervicomediastinal (14). The T cell immunophenotype was over‐represented among the leukaemic cases (P = 0.013). Generally, the T cell immunophenotype predominated except for many affected atypical tissues. Neoplastic cells were mostly of medium nuclear size with round to oval nuclei. No correlations were found for cell morphology, mitotic index and immunopheno‐type. Conclusion The prognostic value of an immunopheno‐typic, anatomical and morphological basis for the classifica tion of lymphoid neoplasia in the koala currently is limited by the need to detect these neoplasms at an early age, the requirement for freshly fixed tissues and the restricted range of available cross‐reacting antibodies.