Therapy-related myelodysplastic syndrome with inv(16)(p13q22) and I type CBFbeta/MYH11 after autologous transplantation: undetectable fusion transcript in pretransplant progenitor cells

Rare type I CBFβ/MYH11 fusion transcript in primary acute myeloid leukemia with inv(16)(p13.1q22): a case report

Inv(16)(p13.1q22) in acute myeloid leukemia (AML) is a common chromosomal abnormality. It leads to the core-binding factor ß-subunit (CBFβ)/smooth muscle myosin heavy chain 11 (MYH11) fusion gene. Different breakpoints were observed in the CBFβ gene at 16q22 and the MYH11 gene at 16p13.1. For this reason, different CBFβ/MYH11 fusion genes are generated, with more than 13 types having been reported to date. Type I CBFβ/MYH11 fusion transcripts are very rare, with only 10 cases being reported to date. This case report describes a primary AML patient with inv(16)(p13.1q22) and a rare type I CBFβ/MYH11 fusion gene. The morphological analysis did not conform to the typical M4eo. Abnormal eosinophils were less than 5%, and there was obvious dysgranulopoiesis. The patient was in hematological and genetic remission for 487 days after the initial chemotherapy cycles. However, the CBFβ/MYH11 fusion had been constantly positive. Moreover, the presence of non-type A fusions may affect its biology and clinical prognosis. Therefore, further studies on understanding its biological and prognostic significance are essential.

Accelerated leukemogenesis by truncated CBF beta-SMMHC defective in high-affinity binding with RUNX1

Dominant RUNX1 inhibition has been proposed as a common pathway for CBF leukemia. CBF beta-SMMHC, a fusion protein in human acute myeloid leukemia (AML), dominantly inhibits RUNX1 largely through its RUNX1 high-affinity binding domain (HABD). However, the type I CBF beta-SMMHC fusion in AML patients lacks HABD. Here, we report that the type I CBF beta-SMMHC protein binds RUNX1 inefficiently. Knockin mice expressing CBF beta-SMMHC with a HABD deletion developed leukemia quickly, even though hematopoietic defects associated with Runx1-inhibition were partially rescued. A larger pool of leukemia-initiating cells, increased MN1 expression, and retention of RUNX1 phosphorylation are potential mechanisms for accelerated leukemia development in these mice. Our data suggest that RUNX1 dominant inhibition may not be a critical step for leukemogenesis by CBF beta-SMMHC.

Detection of the CBFB/MYH11 fusion gene in de novo acute myeloid leukemia (AML): A single-institution study of 224 Japanese AML patients

The cytogenetic findings in acute myeloid leukemia (AML) are a powerful prognostic indicator. Among these abnormalities, the World Health Organization has classified inv(16)(p13q22), which is closely associated with the M4E classification in the French-American-British system, as indicating a good-risk AML. However, this chromosomal abnormality can often be difficult to detect. In this study, we used RT-PCR and FISH analysis to examine 224 Japanese adult de novo AML patients for the presence of the CBFB/MYH11 fusion transcript at the time of diagnosis. The CBFB/MYH11 fusion gene was detected in 17 patients (7.6%): eight patients had the inv(16) chromosome and in all of them it was M4E; nine patients did not have abnormalities in chromosome 16. AML with the CBFB/MYH11 fusion gene but without inv(16) was found in M2, M4, and M5, but not in M4E patients. There were no statistically significant differences in the clinical features of patients with the inv(16) and those with the cryptic inv(16) chromosome. These results indicate that even if eosinophilia is not found, molecular screening for CBFB/MYH11 fusion gene should be performed in all AML patients at the time of diagnosis to help guide disease management.