Variant three-way translocation of inversion 16 in AML-M4Eo confirmed by fluorescence in situ hybridization analysis

Spectral karyotyping and fluorescence in situ hybridization analyses identified a novel three-way translocation involving inversion 16 in therapy-related acute myeloid leukemia M4eo

We report a novel three-way translocation involving inversion 16 and chromosome 12 at bands 16p13, 16q22, and 12q24 in a patient with therapy-related acute myeloid leukemia (AML)-M4eo. Conventional G-banding of bone marrow cells at diagnosis was suggestive of inv(16)(p13q22) and a translocation of chromosomes 12 and 16. The presence of inv(16) was confirmed by reverse-transcription polymerase chain reaction (RT-PCR) analysis, which corresponded to the type A CBFB-MYH11 chimeric transcript. Spectral karyotyping (SKY) analysis clearly identified a reciprocal translocation between chromosomes 12 and 16. In addition, dual-color fluorescence in situ hybridization (FISH) analysis revealed a fusion signal for the CBFB and MYH11 probes and a signal for the MYH11 probe on the der(16) chromosome, as well as a signal for the CBFB probe on the der(12) chromosome. Thus, the karyotype was refined to 46,XX,der(12)t(12;16)(q24;q22),der(16)inv(16)(p13q22)t(12;16). Although we could not establish that this complex chromosomal aberration occurred either as a one-step, three-way event, or a sequential event with inv(16)(p13q22) followed by t(12;16)(q24;q22), SKY in combination with FISH and RT-PCR analyses successfully detected this complex chromosome abnormality in the patient.

Mitoxantrone therapy in multiple sclerosis and acute leukaemia: a case report out of 644 treated patients

As a rare complication of mitoxantrone (MITOX) therapy in multiple sclerosis (MS), a therapy-related acute leukaemia (TRAL) may develop. The incidence is difficult to estimate, as frequently single cases are reported, up to now a total of eight MS patients. Here we report a new case out of 644 patients. This is a 45-year-old female patient with secondary progressive MS who developed TRAL after a total dose of 48 mg/m2 MITOX. The TRAL was classified as acute myeloblastic leukaemia (AML) M4eo and showed an inversion of chromosome 16 and a partial trisomy 11. Her TRAL was treated with chemotherapy followed by allogeneic bone marrow transplantation. It responded well to the transplantation, whereas the MS symptoms initially worsened but have nearly returned to the pretransplantation level. This report brings the currently published frequency of MITOX-associated TRAL in MS therapy to five in a total of 2336 treated MS patients, representing an incidence of 0.21%.

Fluorescence in situ hybridization identifies cryptic t(16;16)(p13;q22) masked by del(16)(q22) in a case of AML-M4 Eo

We report a patient presenting with acute myeloid leukemia (AML)-M4 Eo, in whom conventional cytogenetic analysis revealed a 46, XY, del(16)(q22) karyotype. Molecular analysis of the bone marrow cells using reverse transcriptase polymerase chain reaction (RT-PCR) identified a CBFbeta-MYH11, "type A" fusion transcript. However, despite a thorough reevaluation, a balanced chromosome 16 abnormality could not be definitively identified by cytogenetics. Since there exists a small possibility of obtaining a false-positive PCR result, fluorescence in situ hybridization (FISH) analysis using dual-color, break-apart probes for CBFbeta was performed to elucidate the mechanism of fusion gene formation and thus confirm the RT-PCR results. FISH analysis clearly revealed a cryptic t(16;16), which was probably masked by the del(16)(q22). FISH is the preferred diagnostic procedure to elucidate the CBFbeta-MYH11 fusion in this situation, and resolves the possibility of both false-positive and false-negative results with RT-PCR technique. Due to the improved prognosis of AML associated with the CBFbeta-MYH11 fusion compared to AML generally, we recommend the use of FISH for detection of inv(16)/t(16;16)/CBFbeta-MYH11 in patients with failed, complex, or apparently normal cytogenetics, and in whom the cell morphology indicates the strong possibility of this gene fusion.

Pathogenesis of acute myeloid leukaemia and inv(16)(p13;q22): a paradigm for understanding leukaemogenesis?

Acute myeloid leukaemia (AML) has been proposed to arise from the collaboration between two classes of mutation, a class I, or proliferative, mutation and a class II, or blocking, mutation. A limitation of this so-called 'two-hit' hypothesis has been the lack of identifiable proliferative and blocking mutations in most AML cases. However, it is now known that the CBFbeta-MYH11 fusion gene in AML and inv(16), by disrupting the normal transcription factor activity of core binding factor (CBF), functions as a class II mutation. In addition, nearly 70% of patients with AML and inv(16) are known to possess mutually exclusive mutations of the receptor tyrosine kinases (RTKs), c-KIT and FLT3, as well as RAS genes, that provide a class I, or proliferative, signal. AML and inv(16), therefore, is one of the best understood of the acute leukaemias at the genetic level and so provides a paradigm for the 'two-hit' hypothesis of leukaemogenesis. This paper reviews the recent advances in the molecular pathology of AML and inv(16) and discusses possible therapeutic implications of the current pathogenetic model.

A novel variant three-way translocation of inversion 16 in a case of AML-M4eo following low dose methotrexate therapy

We report a case of acute myelomonocytic leukemia with eosinophilia (AML-M4eo) in a 65-year-old man following low dose methotrexate treatment for pemphigus vulgaris. Cytogenetic studies at diagnosis revealed a complex karyotype including a reciprocal translocation between 11q14.2 and 16q22, an inversion of chromosome 16(p13.1q22), and an apparently terminal deletion of 7q31. The presence of inv(16) was confirmed by reverse transcription-polymerase chain reaction which demonstrated a Type A fusion transcript derived from the core binding factor (CBF) beta and the smooth muscle myosin heavy chain (MYH11) genes. The patient was in complete hematologic and cytogenetic remission 6 months following intensive chemotherapy. Because AML-M4eo with inv(16) has a favorable prognosis, molecular studies should be performed in case the identification of inv(16) by conventional cytogenetics is difficult due to a complex karyotype.