High incidence of t(7;12)(q36;p13) in infant AML but not in infant ALL, with a dismal outcome and ectopic expression of HLXB9

The t(7; 12)(q36;p13) is a recurrent translocation involving the ETV6/TEL gene (12p13) and a heterogeneous breakpoint at 7q36. A fusion transcript between HLXB9 and ETV6 in AML with t(7; 12) is occasionally found. To study the incidence of t(7; 12) in infant and childhood acute leukemia, we screened 320 cases < 36 months using FISH. Additionally, 28 pediatric cases > 36 months with cytogenetic breakpoints at 12p and 7q were investigated. We studied the presence of an HXLB9-ETV6 fusion transcript and quantified the expression of various genes located in the 7q36 breakpoint region. In total, six AML patients carried the t(7; 12) of which five were infants and one child of 18 months. Only one out of 99 infant ALL patients harbored the t(7; 12). No t(7;12) was found in older children with AML or ALL. AML patients carrying a t(7; 12) had a poor outcome with a 3-year EFS of 0%. A fusion of HLXB9 to ETV6 was found in four AML cases with t(7;12). The 7q36 genes NOM 1, LMBR1, RNF32, and SHH were equally expressed among t(7; 12)-positive AML versus t(7;12)-negative AML, t(7;12)-negative ALL, or normal bone marrow. However, the HLXB9 expression was highly increased in t(7;12)-positive cases, including those with an HLXB9-ETV6 fusion. We conclude that the t(7;12) is almost exclusively present in infant AML and covers 30% of infant AML, while it is extremely rare in infant ALL and older children. The t(7; 12) is associated with a poor outcome and an ectopic expression of HLXB9 is commonly involved in this genetic subtype of leukemia. (c) 2006 Wiley-Liss, Inc.