Is trisomy 22 in acute myeloid leukemia a primary abnormality or only a secondary change associated with inversion 16?

Core-binding factor acute myeloid leukemia: Heterogeneity, monitoring, and therapy

Core binding factor acute myelogenous leukemia (CBF AML) constitutes 15% of adult AML and carries an overall good prognosis. CBF AML encodes two recurrent cytogentic abnormalities referred to as t(8;21) and inv (16). The two CBF AML entities are usually grouped together but there is a considerable clinical, pathologic and molecular heterogeneity within this group of diseases. Recent and ongoing studies are addressing the molecular heterogeneity, minimal residual disease and targeted therapies to improve the outcome of CBF AML. In this article, we present a comprehensive review about CBF AML with emphasis on molecular heterogeneity and new therapeutic options.

Prognosis and monitoring of core-binding factor acute myeloid leukemia: current and emerging factors

Core-binding factor acute myeloid leukemia (CBF-AML) - including AML with t(8;21) and AML with inv(16) - accounts for about 15% of adult AML and is associated with a relatively favorable prognosis. Nonetheless, relapse incidence may reach 40% in these patients. In this context, identification of prognostic markers is considered of great interest. Due to similarities between their molecular and prognostic features, t(8;21) and inv(16)-AML are usually grouped and reported together in clinical studies. However, considerable experimental evidences have highlighted that they represent two distinct entities and should be considered separately for further studies. This review summarizes recent laboratory and clinical findings in this particular subset of AML and how they could be used to improve management of patients in routine practice.

Concurrent acute myeloid leukemia with inv(16)(p13.1q22) and chronic lymphocytic leukemia: molecular evidence of two separate diseases

Acute myeloid leukemia (AML) occurring concurrently with or after untreated chronic lymphocytic leukemia (CLL) is rare. We report a case of a 59-year-old man who was evaluated for anemia, thrombocytopenia, and leukocytosis with circulating blasts. On the basis of the morphology and immunophenotyping results, a preliminary diagnosis of chronic myelomonocytic leukemia with concurrent CLL was considered. Subsequently, cytogenetic analysis of the leukemic blood specimen revealed inv(16)(p13.1q22) with secondary trisomy 22 in a sideline clone. Fluorescence in situ hybridization confirmed the CBFbeta rearrangement associated with inv(16) in myeloblasts and myelomonocytic cells, but not in CLL cells. Therefore, a final diagnosis of AML with inv(16) with concurrent CLL was made. After standard chemotherapy for AML, the patient achieved complete remission for both his AML and CLL. The unique aspects of this case include concomitant AML and CLL, which do not share clonality, complex cytogenetic abnormalities with trisomy 22 as a secondary abnormality associated with inv(16), and achievement of remission for both AML and CLL by AML chemotherapy regimen. This case also represents one of the rare instances where a diagnosis of AML can be established even when the blast percentage in the marrow and blood is less than 20%.

Acquired Robertsonian translocations are not rare events in acute leukemia and lymphoma

Robertsonian translocations are the most common constitutional structural abnormalities but are rarely reported as acquired aberrations in hematologic malignancies. The nonhomologous acrocentric rearrangements are designated as Robertsonian translocations, whereas the homologous acrocentric rearrangements are referred to as isochromosomes. Robertsonian rearrangements have the highest mutation rates of structural chromosome rearrangements based on surveys of newborns and spontaneous abortions. It would be expected that Robertsonian recombinations would be more common than suggested by the literature. A survey of the cytogenetics database from a single institution found 17 patients with acquired Robertsonian rearrangement and hematologic malignancies. This is combined with data from the literature for a total of 237 patients. All of the possible types of Robertsonian rearrangements have been reported in hematologic malignancies, with the i(13q), i(14q), and i(21q) accounting for nearly 60%. Complex karyotypic changes are seen in the majority of cases, corresponding with disease evolution. These karyotypes consistently show loss of chromosomes 5 and/or 7 in the myelocytic disorders, nonacrocentric isochromosomes, and centromeric breakage and reunion. However, nearly 25% of the acquired rearrangements were found as the sole abnormality or in addition to an established cytogenetic aberration. Most of these were the i(14q) with the myelodysplasia subtypes refractory anemia and chronic myelomonocytic leukemia.

Comparison of cytogenetic and molecular genetic detection of t(8;21) and inv(16) in a prospective series of adults with de novo acute myeloid leukemia: a Cancer and Leukemia Group B Study

PURPOSE

To prospectively compare cytogenetics and reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22), aberrations characteristic of core-binding factor (CBF) acute myeloid leukemia (AML), in 284 adults newly diagnosed with primary AML.

PATIENTS AND METHODS

Cytogenetic analyses were performed at local laboratories, with results reviewed centrally. RT-PCR for AML1/ETO and CBFbeta/MYH11 was performed centrally.

RESULTS

CBF AML was ultimately identified in 48 patients: 21 had t(8;21) or its variant and AML1/ETO, and 27 had inv(16)/t(16;16), CBFbeta/MYH11, or both. Initial cytogenetic and RT-PCR analyses correctly classified 95.7% and 96.1% of patients, respectively (P =.83). Initial cytogenetic results were considered to be false-negative in three AML1/ETO-positive patients with unique variants of t(8;21), and in three CBFbeta/MYH11-positive patients with, respectively, an isolated +22; del(16)(q22),+22; and a normal karyotype. The latter three patients were later confirmed to have inv(16)/t(16;16) cytogenetically. Only one of 124 patients reported initially as cytogenetically normal was ultimately RT-PCR-positive. There was no false-positive cytogenetic result. Initial RT-PCR was falsely negative in two patients with inv(16) and falsely positive for AML1/ETO in two and for CBFbeta/MYH11 in another two patients. Two patients with del(16)(q22) were found to be CBFbeta/MYH11-negative. M4Eo marrow morphology was a good predictor of the presence of inv(16)/t(16;16).

CONCLUSION

Patients with t(8;21) or inv(16) can be successfully identified in prospective multi-institutional clinical trials. Both cytogenetics and RT-PCR detect most such patients, although each method has limitations. RT-PCR is required when the cytogenetic study fails; it is also required to determine whether patients with suspected variants of t(8;21), del(16)(q22), or +22 represent CBF AML. RT-PCR should not replace cytogenetics and should not be used as the only diagnostic test for detection of CBF AML because of the possibility of obtaining false-positive or false-negative results.

Molecular and clinical advances in core binding factor primary acute myeloid leukemia: a paradigm for translational research in malignant hematology

Clonal chromosomal abnormalities are the most important prognostic indicators in acute myeloid leukemia (AML). Recent advances in molecular biology have allowed structural and functional characterization of many of these genomic rearrangements and have provided evidence for their primary role in leukemogenesis. Two of the most prevalent cytogenetic subtypes of adult primary or de novo AML, t(8;21)(q22;q22) and inv(16)(p13q22), are characterized by disruption of the AML1(CBF alpha 2) gene at 21q22 and the CBF beta gene at 16q22, respectively. Both genes encode a subunit of core binding factor (CBF), a regulator of normal hematopoiesis. At the molecular level, t(8;21)(q22;q22) and inv(16)(p13q22) result in the creation of novel fusion genes, AML1/ETO and CBF beta/MYH11, whose structures and functions are being successfully characterized by in vitro studies and transgenic animal models. Detection of t(8;21)(q22;q22) or inv(16)(p13q22) in adult patients with primary AML is a favorable independent prognostic indicator for achievement of cure after intensive chemotherapy or bone marrow transplantation and may serve as a paradigm for risk-adapted treatment in AML. The purpose of this review is to summarize the recent advances in the molecular biology and clinical management of t(8;21)(q22;q22) and inv(16)(p13q22) primary AML, collectively referred to here as CBF AML.

Typical CBFbeta/MYH11 fusion due to insertion of the 3'-MYH11 gene into 16q22 in acute monocytic leukemia with normal chromosomes 16 and trisomies 8 and 22

In a case of acute monocytic leukemia, M5a according to the FAB classification, with a 48,XY,+8,+22 karyotype, amplification of the CBFbeta/MYH11 fusion transcript type A was detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Fluorescence in situ hybridization (FISH) using an appropriate panel of DNA probes showed that insertion of the 3'-MYH11 within the CBFbeta gene on chromosome 16q22 was the mechanism producing the same molecular rearrangement as in typical inv(16)(p13q22)/t(16;16)(p13;q22).

CBFB/MYH11 fusion in a patient with AML-M4Eo and cytogenetically normal chromosomes 16

We present a unique case of acute myeloid leukemia M4Eo (AML-M4Eo) with a CBFB/MYH11 fusion transcript and a trisomy 22, but in whom cytogenetic analyses did not disclose an inv(16). Fluorescence in situ hybridization (FISH) analysis with chromosome arm-specific painting probes as well as with the c40 and c36 cosmids also revealed no evidence for an inv(16), whereas the application of locus-specific probes confirmed the presence of a masked inv(16). The results of our comprehensive FISH investigations indicate that the events leading to this masked inv(16) were complex and concurred with deletions on both the long and short arms. The most likely explanation for the formation of the relevant CBFB/MYH11 fusion is an insertion of parts of the MYH11 into the CBFB gene, although it is also possible that it was formed by a double inversion.

Trisomy 22 in acute myeloid leukemia: a marker for myeloid leukemia with monocytic features and cytogenetically cryptic inversion 16

Trisomy 22 is an uncommon chromosomal abnormality in acute myeloid leukemia. Recent studies, however, have shown an association between trisomy 22 and acute myeloid leukemia with a monocytic component, and in particular, acute myelomonocytic leukemia with marrow eosinophilia. Furthermore, it has also been suggested that trisomy 22 was in fact only a secondary chromosomal change occurring in acute myeloid leukemia with inv(16). In this report, we analyze the morphological, cytogenetic, and molecular findings of three cases of acute myeloid leukemia with trisomy 22 but without cytogenetic evidence of inv(16). The results indicate a consistent association between trisomy 22 and inv(16), the latter being cytogenetically cryptic in some cases. This finding is of potential diagnostic and therapeutic significance.

"Jumping translocation" in a 17-month-old child with mixed-lineage leukemia

A 17-month-old child with acute biphenotypic (pre B-ALL/myelomonocytic) leukemia is reported. Extensive cytogenetic analysis performed at various stages of the disease revealed a clonal evolution at the time of initial diagnosis with two types of abnormal clones, one with trisomy 22 and two other related clones with trisomy 22 plus partial trisomy of the long arm of chromosome 1 associated with the telomeric segment of either chromosome 20q or 21p. At the time of relapse the only abnormal clone involved trisomy 22 and partial trisomy of 1q, but this time in association with the telomeric segment of 14p. The unique feature of these translocations is discussed and the possibility of the correlation between the different chromosomal abnormalities and the expression of biphenotypic markers is raised.