Acute Lymphocytic Leukemia in the Latin American Population

Introduction: An interesting epidemiological aspect of ALL is the variation between ethnic groups. Among all subtypes of leukemia Latinos have lower incidence rates. However, in remarkable contrast, ALL has a higher incidence rate in the Latino population and also carries a more dismal prognosis (Barrington-Trimis J, et al Blood 2015).

The majority of reported data among Latinos either exclusively looks at B cell precursor (BCP) ALL or does not distinguish between subtypes. In this study we used the National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) database to delineate the differences in incidence rates of B-ALL and T-ALL across ethnic groups in the United States.

Epidemiologically, highest rates of ALL worldwide have been reported in both adult and pediatric Latino patients. However, determining who is to be considered Latino is not always straightforward. Many studies utilize self reported ethnicity and databases such as the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute (NCI) employ complex algorithms to determine ethnicity. Of note, the North American Association of Central Cancer Registries (NAACCR) Hispanic Identification Algorithm (NHIA) used by SEER includes European Spaniards but excludes South American Brazilians. This is a point of special interest due to the fact that although the overall incidence of ALL in the Brazilian population is low, the regional distribution is strikingly heterogeneous, with higher rates in regions with higher indigenous ancestry.

Methods: Data from the SEER-18 database was used compare incidence rates of T-ALL and B-ALL. Patients in which ethnicity was reported were included. Due to the utilization of cytogenetics and subsequent changes in ICD coding over the years we chose to look at the most recent data reported in 2014. We compared rates in non-Hispanic Whites, Latinos (Hispanic), Blacks and Asian-Pacific Islanders (API). Age-adjusted incidence rates per 100,000 person-years were calculated.

Results: AAIR of B-ALL in the Hispanic population is consistently higher than that of Non-Hispanic Whites throughout the years, ranging from 1.0-2.4 per 100,000. Blacks had the lowest incidence overall, with rates approximately one third of those found in Latinos.

The distribution of ALL throughout the Americas can perhaps shed some epidemiological light on the genetic origins of ALL in Latinos. The ancestry across Latin America is mixed but historical idiosyncrasies can perhaps explain the distribution of ALL in the Americas. We reviewed the available literature and found that throughout the Americas, higher incidence rates are seen in areas of higher Native American ancestry (Fig 1).

Discussion:

Our finding shows that the increase of ALL among Latinos is accounted for by the high rate of B cell origin. The increased incidence of ALL in the Latino population has been linked to polymorphisms in genes such as the transcription factor GATA3 (Perez-Andreu V, Nat Genet 2013). The underlying mechanism of disease has yet to be elucidated and is likely related to BCP- ALL and, more specifically, Ph-Like ALL. This variation appears to be related to Native American ancestry. Understanding the molecular mechanism and epidemiological origins of this subset of patients with aggressive features will lead to improved treatment and overall survival in this minority healthcare disparity.

Figure 1.

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Figure 1.

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