According to a tendency of an increase of acute leukemia in the aged people, we have recently seen not a few patients with acute leukemia of an atypical variety. These cases "smolder along" with mild clinical features for a period of months to years. They were designated as "smoldering acute leukemia" by Rheingold in 1963. The author summarised the clinical and hematological features of one's own experienced cases of acute leukemia belonging to this category. The author intended further to find the possible causes inducing these atypical clinical courses through cytogenetic analysis of leukemic cells in the bone marrow, and obtained the following results. 1. Clinical Studies 1) Six of 7 cases were males and 5 cases were the aged patients over 50 years. Five of 7 cases did not reveal any typical signs and symptoms indicating acute leukemia, such as high grade fever, severe bleeding tendency, hepatosplenomegaly or lymphadenopathy. 2) In the peripheral blood, all of them were aleukemic, i.e., none did show leukocytosis, 0 to 10% at most of leukemic blasts were found. 3) In the bone marrow, 5 of them showed hypoplastic marrow and the other 2 cases normoplastic and hyperplastic. High percentage of leukemic myeloblasts or promyelocytes were observed in all cases. 4) No antileukemic agents except the minimum dose of steroid hormon and repeated intermittent blood transfusion were given to the patients. The patients survived over one year except one case that died of pneumonia at 8.5 months after treatment was started.
Ⅱ. Cytogenetic Studies Cytogenetic studies were done on bone marrow samples using a modification of the direct method of Tjio and Whang. 1) Four of 7 cases revealed a normal diploid mode with 46 chromosomes. Aneuploidy was however, found in the remaining three cases, one case of hypodiploidy with 45 chromosomes and 2 cases of hyperdiploidy with 47 chromosomes. 2) Four of 7 cases revealed a normal karyotype, wheras the other three cases revealed a remarkable changes of karyotype. 3) The chromosome anomaly common to all cases were not found. 4) No significant relationship was observed between the clinical features of these cases and their chromosome anomalies of the leukemic cells in the bone marrow. From these results it is concluded that the atypical clinical course of the smoldering acute leukemia is not controled solely by the cytogenetic factors of the leukemic cells.