The relative effectiveness of 6-MP and busulfan for the achievement and maintenance of control of chronic granulocytic leukemia over a period of 12 weeks has been studied. In a randomized study, 15 patients received 6-MP and 9 busulfan. In addition, results of a similar study in which 31 patients were treated with busulfan were combined with the current study. Sequential studies in which patients received more than one course of study were made in 11 patients so that altogether 62 studies were completed in 49 patients.

6-MP produced "good" or "excellent" responses in only 5 (33 per cent) of 15 trials, whereas, 42 (89 per cent) of 47 trials using busulfan responded to this degree.

Busulfan is superior to 6-MP for the over-all control of chronic granulocytic leukemia during a 12-week course of study. Not only are the results obtainable with 6-MP inferior to those with busulfan, but 6-MP is also more difficult to use.

Busulfan in the dosage used reduces the granulocyte count somewhat more slowly than does 6-MP, but the effect is more prolonged. The escape of the granulocytes from depression by 6-MP is very rapid.

The reduction of platelet counts from abnormally high levels to normal is more effectively achieved with busulfan than with 6-MP since, in doses sufficient to reduce the granulocyte count, the latter drug is less likely to affect the level of platelet counts than is busulfan.

It may be possible to exploit these differences occasionally. If a patient becomes difficult to control with busulfan because of thrombocytopenia, 6-MP may offer control with greater safety. In patients whose marrow function is especially susceptible to depression with busulfan, 6-MP may offer the safety valve of a more rapid escape from overtreatment.

In general, 6-MP is not recommended for the routine management of chronic granulocytic leukemia prior to the development of the blast stage.

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© 1963 by American Society of Hematology, Inc.
1963
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