Oral extramedullary plasmacytomas (EMP) are locally aggressive tumors in the dog that rarely metastasize. They represent 5.2% of all canine oral tumors and 22.0 to 28.0% of all EMPs diagnosed are in the oral cavity. EMPs consist of neoplastic plasma cells that do not arise from the bone marrow. No relationship between EMP and the development of multiple myeloma has been determined in dogs. Complete surgical excision is the primary treatment for this neoplasm and is usually curative. Multiple oral EMPs within the same patient have been rarely reported with tumors arising in the same location in the mouth. To the authors' knowledge, multicentric oral EMP, as described in the following cases, has not been reported in the dog.

Mouse bone marrow forms colonies of granulocytes and monocytic phagocytes when cultured in the presence of human plasma, urine or "feeder layers" prepared from human leukocytes. By contrast, human marrow produces colonies i n the presence of leukocyte feeder layers but not in the presence of plasma or urine. It has been tacitly assumed that the response of mouse marrow to human blood leukocyte feeder layers is a measure of physiological substances released by those leukocytes which might control human granulopoiesis. This assumption however, has never been put to the test by comparing the response of mouse and human marrow to stimulation by leukocytes from the same individual. This has been done in the present study by using leukocytes from normal and leukemic subjects. Different human marrows responded similarly to stimulation by the same normal feeder layers, but there was no quantitative or qualitative correlation between the response of human and mouse marrows. Feeder layers from patients with acute granulocytic leukemia did not stimulate colony growth in normal human marrow but were as potent in stimulating mouse marrow colony growth as were feeder layers of normal leukocytes.We conclude that different factors may stimulate human and mouse marrows and that assays of granulopoietic factors of human origin should in future be carried out in human rather than mouse marrows.

Culture of bone marrow and/or blood cells in a semisolid agar system from 43 adults with acute nonlymphoblastic leukemia at first presentation showed two distinct growth patterns at 14 days. In 53% of patients cells failed to grow (type O), while in the remainder an abnormal growth pattern (type B) with small numbers of diffuse colonies and excessive numbers of cell clusters was seen. The response following chemotherapy was significantly better in the patients whose cells failed to grow. Serial culture studies, performed in 9 patients throughout remissions of 100–1112 days, which had been maintained by intermittent chemotherapy, showed wide fluctuations in proliferative activity. These ranged from no growth to marked proliferation with predominance of clusters and small numbers of diffuse colonies, indistinguishable from the type B pattern seen in 47% of patients at first presentation. The possibility is discussed that the periods of failure to grow, and/or those in which a type B pattern emerged, represented sporadic reactivation of leukemic cells.