Acute promyelocytic leukaemia in patients originating in Latin America is associated with an increased frequency of the bcr1 subtype of the PML/RARα fusion gene

Summary. The PML/RARα fusion gene in acute promyelocytic leukaemia (APL) has three subtypes based on the breakpoint site of the PML gene: long (bcr1), short (bcr3) and variable (bcr2) subtypes. The PML/RARα fusion protein is involved in the pathogenesis of APL and the breakpoint site of the PML gene might be associated with aetiological factor(s). Because APL is over‐represented in patients that originate in Latin America (Latinos), we evaluated whether the distribution of the PML/RARα fusion mRNA in this population is different to that reported in non‐Latinos. Among 52 APL patients (28 from Mexico and Central America diagnosed in Los Angeles and 24 from Peru, South America), bcr1, bcr2 and bcr3 expression was 75%, 10% and 15% respectively. However, bcr1 breakpoints were significantly higher compared with non‐Latino patients (340/654, 52%) reported in four studies. Often bcr1 and bcr2 are reported together; 862 (60%) of 1429 non‐Latino APL patients reported in nine studies were either bcr1 or bcr2, compared with 44 (85%) in our 52 Latino patients. This difference was also statistically significant when our patients were compared to each of the individual studies from USA and Europe, but not for a small series from China and Japan. These results suggest that the overrepresentation of APL among Latin American patients can be accounted for by an increase of a single subtype – bcr1, and the breakage sites in the PML gene may not be random but possibly influenced by genetic and/or environmental factor(s).