The inv(16) cytogenetic subtype of acute myeloid leukemia (AML) has a relatively good prognosis. Many patients achieve complete remission (CR). The prognostic uncertainty of negative qualitative reverse transcription-polymerase chain reaction (RT-PCR) assays suggests the need to identify prognostically significant critical thresholds by real-time RT-PCR. A reliable and sensitive (10 ؊5 ) real-time RT-PCR assay was set up for the evaluation of relevant CBF-MYH11/ABL transcript ratios and was applied to the 21 patients with inv(16) AML routinely referred for cytogenetic and molecular monitoring in Serà gnoli Institute (Bologna, Italy) since 1990. Among the 18 patients who underwent ablative chemotherapy, all achieved CR with a 3-year disease-free survival probability of 63% (95% CI, 40%-87%) and no recorded events after 26 months. Five patients had relapses; 2 died of disease and 3 entered second CR. Analysis of the 125 bone marrow (or peripheral blood) samples studied by real-time RT-PCR showed that transcript ratios of samples taken during CR at any time before a relapse were always greater than 0.12%, whereas those of samples taken during first or second CR from patients who did not subsequently have relapses were always less than 0.25%. This suggests that transcript ratios greater than 0.25% may correspond to high risk for relapse, whereas ratios below 0.12% might indicate the patient is in a curable state.
IntroductionInversion of chromosome 16, inv(16)(p13q22), and its related translocation, t(16;16)(p13;q22), are recurrent rearrangements found in a subset of patients with acute myeloid leukemia (AML), particularly the M4Eo subtype. [1][2][3][4] Inv(16) is associated with relatively good long-term, disease-free survival (DFS). 5,6 It generates a chimeric mRNA transcript, CBF-MYH11, by fusing the CBF gene located on band q22 of chromosome 16 7,8 and the MYH11 gene, which encodes a heavy chain of the smooth-muscle myosin protein, located at the p13 breakpoint. 9,10 Messenger RNA analysis by reverse transcription-polymerase chain reaction (RT-PCR) can help define leukemic subsets and provide potentially valuable diagnostic and prognostic information. 11 Qualitative RT-PCR reveals the presence of detectable levels of minimal residual disease (MRD) in patients in complete clinical remission (CR) after induction chemotherapy. 12 Introduction of real-time RT-PCR 13 should allow routine quantitation of the transcript. The 5Ј-3Ј nuclease activity of the Taq polymerase cleaves an internal fluorogenic probe specific for the target sequence, causing the emission of a fluorescent signal that can be detected during amplification. This allows rapid quantitation of specific RT-PCR products with a dynamic detection range of more than 5 orders of magnitude. Several groups have used real-time RT-PCR with TaqMan technology to quantitate MRD with leukemia-specific chromosome aberrations such as t(9;22), t(l5;17), and t(8;21). [14][15][16] Most patients with inv(16) AML treated in our institute achieved long-term CR. 17,18 Ho...