TREATMENT OF LEUKEMIA AND RELATED DISORDERS WITH 6‐MERCAPTOPURINE

Since February 1953, 48 patients d i c t e d with leukemia and allied disorders have received 6-mercaptopurine a t the University of Michigan Hospital and a t the Simpson Memorial Institute. Eight of the patients died within three weeks of the time of institution of therapy, most of them receiving the drug for less than one week. The remaining 40 serve as the clinical material for the analysis of our therapeutic results. It is recognized that for comparisons of antileukemia agents from the standpoint of survival, all cases should be included. However, such a comparison is not possible for our series because of previous or subsequent use of agents other than 6-mercaptopurine in many instances. I t is our purpose to evalute the nature of the response obtained with 6-mercaptopurine in those patients who received the drug alone for a sufficient time to permit observation of its effect. Our practice is largely confined to adults, and in the series of 40 cases only five patients were under 1.5 years of age. I t soon became evident that our better therapeutic responses were being obtained in younger adults, and that the most satisfactory dividing line appeared to be a t 35. This is an arbitrary separation, of course, but one cannot help being impressed with the inability of the middle-aged and elderly patient having acute leukemia to restore any degree of normal hemopoiesis, even though leukemic cell proliferation is suppressed. Factors which influence the responsiveness of a case of leukemia to specific medication, include, in addition to the age of the patient, the cell type, the proliferative activity, and the degree of dedifferentiation. Duration of the disease before institution of treatment bears a relation to the therapeutic response, but this variable cannot be controlled or readily defined, and it may be expected to affect more or less equally the several categories of acute leukemia. The most undifferentiated type is the stem cell or hemocytoblastic. Those showing some cellular differentiation are the lymphocytic, granulocytic, and monocytic. Less rapidly proliferating forms of leukemia are classed as subacute. Most subacute leukemias are granulocytic, and this type only is represented in the present series. Chronic leukemias show variable rates of cell proliferation and, until they become advanced, exhibit a relatively high degree of cell differentiation. In addition to these forms there are the disseminated lymphocytic sarcoma and reticulum cell sarcoma, both of which may be leukemic. Employing the criteria for good and partial remissions suggested for the conference on 6-mercaptopurine on which this monograph is based, our results may be summarized as follows: There were three cases of acute hemocytoblastic leukemia, all under 35 years of age. Two of these patients had good remissions, and one a partial remission. The rapidly proliferating leukemias are classed as acute.