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Histological, enzyme histochemical and ultrastructural findings in three cases of feline bone marrow neoplasia are described. The following changes were observed: in myelodysplastic syndrome (MDS), a low medullary blast count, strongly atypical (micromegakaryocytic) proliferative megakaryocytopoiesis, hypoplastic erythrocytopoiesis with impairment of differentiation, multifocal extravasation and lymphoid aggregates; in acute myeloid leukaemia (AML), medullary proliferation of undifferentiated cell types; in chronic myeloIproliferative disorder (CMPD), trilinear medullary proliferation with complete cellular maturation, osteomyelosclerosis and extramedullary haemopoiesis. In two cases (MDS, AML), ultrastructural demonstration of C-type virus particles (feline leukaemia virus) suggested a viral aetiology., (Copyright 1999 Harcourt Publishers Ltd.)

A myeloproliferative disease was found in a 128-day-old Holstein female calf. The tumour consisted chiefly of primitive cells, and more mature cells, many of which were positive for haemoglobin, were admixed with them. Binucleated cells at various stages of maturation were occasionally seen, and siderosomes were confirmed in both primitive cells and more mature cells by electron microscopy. The primitive cells resembled proerythroblasts, and this tumour, thought to be an acute type neoplasm of the erythroid system, was distinguishable from chronic erythremic myelosis and polycythemia vera.

A cat with feline leukaemia virus-associated malignant disease was treated by ex vivo immunoadsorption using staphylococcal protein A coated filters. During the 12-week course of treatment, the morphological manifestations of the haematopoietic disease showed a progressive transition from erythroid to myeloerythroid to myeloid predominance, and the disease was preceded by and associated initially and terminally with a blast transformation of lymphoblastic morphology. Necropsy revealed massive meningo-cerebral, as well as hepatic, renal, myeloid, lymphoid, peritoneal and pelvic infiltrations largely consisting of lymphoblastic cells. Evidence of myeloid and erythroid differentiation was present in all the infiltrates. The several possible bases for this shift of morphological expression are considered.

A case of granulocytic myeloproliferative disease with hypercalcaemia of malignancy in a 6-year-old Golden Retriever dog is described. Numerous retrovirus-like budding particles were observed at the cell surface of the neoplastic granulocytes, suggesting the presence of a new oncogenic virus. Several attempts by other workers to demonstrate the presence of an oncogenic retrovirus in canine lymphosarcoma have produced minimal results. This study suggests that non-lymphoid canine myeloproliferative disorders warrant further investigation.

Light, electron, and immunofluorescence microscopy on tissues from 63 domestic cats revealed that glomerulonephritis occurred in almost one third of cats with hematopoietic neoplasms of the type linked with feline leukemia virus (FeLV). Glomerular lesions were of the immune complex type with subepithelial, subendothelial, and mesangial dense deposits and reticular aggregates, similar to the nephropathy associated with systemic lupus erythematosus in humans. Evidence that the glomerular lesions may be viral-induced raises the possibility of similar pathogenetic mechanisms in human disease.