A novel cryptic CBFB-MYH11 gene fusion present at birth leading to acute myeloid leukemia and allowing molecular monitoring for minimal residual disease

Acute myeloid leukemia (AML) with the inv(16)/t(16;16) karyotype is associated with a favourable prognosis, showing longer periods of complete remission and high overall survival rates. Here we report a four year old girl, who presented with pallor, a history of viral infections and pancytopenia, an abnormal karyotype, but initially no signs of leukemia. After one month, molecular diagnostics revealed a rare CBFB/MYH11 fusion variant transcript type S/I, leading to the diagnosis of CBF AML. Additional FISH confirmed the presence of a cryptic CBFB/MYH11 fusion. We developed a nested PCR test for the CBFB/MYH11 fusion gene transcript S/I to monitor this patient for minimal residual disease. Eleven months after complete remission this transcript was still absent in peripheral blood samples.