Acute Childhood Leukemia in Johannesburg: Ethnic Differences in Incidence, Cell Type, and Survival

Acute childhood leukemia was found to be less common in black children than in white children in the Johannesburg area of South Africa. Of 195 consecutive patients, 78 were black and 117 white. The annual incidence was 0.8/100,000 black children and 3.3/100,000 white. The low incidence in black children was due to the very low incidence of acute lymphoblastic leukemia (ALL), which was 0.41/100,000 black children compared with 2.73/100,000 white children. The incidence of acute non-lymphoblastic leukemia (ANLL) was approximately the same for both ethnic groups; 0.38/100,000 black children and 0.57/100,000 white children. Remission rates for black children with ALL were lower than for white children and the cumulative proportion of black patients surviving at 60 months was only 32% compared with 72% of white patients (p = 0.0001). The most significant poor prognostic factors in ALL were ethnic group and age (p = 0.0006), CNS disease at onset (p = 0.006), FAB L2 and L3 morphology (p = 0.05), and irregular clinic attendance during maintenance therapy (p = 0.05). In ANLL, remission and survival rates were less favorable than in ALL but there were no significant differences between black and white patients. Black patients exhibited certain clinical features rarely seen in white patients, including chloromata, oropharyngeal lesions, and CNS involvement at onset. Karyotypic abnormalities were common. The most significant poor prognostic factors in ANLL were CNS disease at onset (p = 0.03), generalized lymphadenopathy (p = 0.0001), and FAB morphology classification M3-M6 (p = 0.05). Certain patients with FAB M1 and M2 morphology appeared to have the potential for long-term survival. The possible significance of these findings in relationship to ethnic and environmental factors is discussed.