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Some patients present borderline features between acute myeloid leukemia (AML) and typical myelodysplastic syndromes (MDS): an excess of blasts insufficient to conclusively diagnose AML, yet above the figures usually compatible with MDS or the presence of Auer rods associated with a moderate excess of blasts. This presents considerable difficulties in diagnosis and management. The authors studied 28 such cases using the French-American-British Co-operative Group (FAB) classification, which groups them into a separate category termed "refractory anemia with excess of blasts in transformation" (RAEB-T). This was found to be a heterogenous group. Certain patients (4/28) had a previously established myelodysplasia, but most presented directly as RAEB-T. Two very different pictures emerged: a few patients (4/28) were young, with presentation and evolution similar to classic AML, for whom combination chemotherapy was effective; the majority (20/28) were older, with more varied clinical and cytologic presentation, for whom chemotherapy was of little effect and who presented a picture resembling classic RAEB with a median survival of 10 months.

Twelve cases of pure acute monocytic leukemia in adults were studied. They were selected on the basis of the morphology of the blast cells on Romanowsky-stained smears of blood and bone marrow, as well as positivity of the cells for the naphthol ASD acetate esterase reaction specifically inhibited by sodium fluoride. There was no sex predominance. Neoplastic involvement of the skin and/or gingiva was very frequent. The leukemic proliferation in blood and bone marrow consisted of monoblasts, promonocytes and monocytes. The peroxidase reaction was negative or only faintly positive. Serum and urinary lysozyme levels were increased. The blast cells retained their ability to stimulate, in vitro , colony formation by normal bone marrow cells used as targets. All of these characteristics permit specific identification of this type of acute leukemia. The prognosis is grim: only five of 12 patients achieved complete remission, and four of these five had relapses in less than 14 months; the median survival was five months.

The use of in-vitro culture methods for studying human haemopoietic cells has advanced greatly since 1970. These methods have contributed to our understanding of the mechanisms controlling granulopoiesis though the physiological role of colony-stimulating factor needs further clarification. In leukaemia they offer an approach to the study of possible causal factors and to the characterisation of leukaemiccell defects. Results already obtained support the concept that the bone-marrow in acute myeloid leukaemia consists of coexisting populations of normal and leukaemic cells, with a leukaemic clone predominating in relapse and normal clones regenerating in remission. For the individual patient, in-vitro methods may prove useful in assessing prognosis and in confirming the completeness of remission, the detection of early relapse may then indicate the need for changing or re-instituting therapy. Further studies may aid the classification of the "preleukaemic" states and may help in the identification of the various causes of neutropenia.

Serum cobalamin (vitamin B12) and unsaturated B12 binding capacity (UBBC) have been measured in 24 cases of hypereosinophilia: 16 were cases of hypereosinophilic syndrome (HES) and 8 of secondary eosinophilia. The two groups were similar with respect to absolute eosinophil counts. Serum cobalamin and UBBC were found to be markedly increased in most cases of HES and normal in secondary eosinophilia. This elevation of UBBC was mainly related to the increase of R binders (transcobalamins I and III). The elevated serum cobalamin and R binders in HES were due neither to a higher intracellular content of R binders nor to an increased release of these binders from eosinophils of HES. Pure fractions of eosinophils obtained from HES and secondary eosinophilia did not exhibit any difference in vitamin B12 binders. On the other hand, neutrophil-rich fractions from the same patients showed a higher content of intracellular B12 binding proteins than pure eosinophil fractions, irrespective of the cause of eosinophilia. These findings suggest that the increased serum vitamin B12 and UBBC could reflect an expanded pool of both eosinophils and neutrophils in HES and, thus, provide an additional argument for the inclusion of this syndrome in the group of myeloproliferative disorders.