THYMIC LYMPHOSARCOMA OF T-CELL LINEAGE IN A KOALA (PHASCOLARCTOS-CINEREUS)

Objective To diagnose and characterise thymic lymphosarcoma in a koala . Design A pathological case. Animal Seven-year-old female kaola. Proc edure The neoplastic process was investigated macroscopically, haemato logically, histologically and immunohistologically. Results The koala had difficulty swallowing because of a medial swelling in the lower ne ck. Biopsy of this mass and blood examination revealed lymphosarcoma w ith a leukaemic manifestation; necropsy and histopathological examinat ion showed the mass to be thymus. Palatine tonsils, cervical, axillary and mesenteric lymph nodes, spleen, liver, gut, bronchi, genitalia an d bone marrow were infiltrated by neoplastic cells. Immunohistological staining of the thymic mass, cervical and mesenteric lymph nodes, bon e marrow, spleen and gut revealed the neoplastic cells to be of T lymp hocyte origin (positive for both anti-human CD3 and CD5). Conclusions It is speculated that the neoplastic process originated in the thymus and was disseminated by blood-borne neoplastic cells. This first repor t of thymic lymphosarcoma in a marsupial confirms that antibodies rais ed originally to investigate human lymphoid neoplasia can cross-react with neoplastic lymphocytes in koalas.