Variant Three-Way Translocation of Inversion 16 in AML-M4Eo Confirmed by Fluorescence In Situ Hybridization Analysis

The inv(16) and t(16;16) characterize a subgroup of acute myelomonocytic leukemia (AML) with distinct morphological features and a favorable prognosis. Both cytogenetic abnormalities result in a fusion of CBFβ at 16q22 and MYH11 gene at 16p13, whose detection by PCR and fluorescence in situ hybridization (FISH) is useful for diagnosis and monitoring of the disease. Variant translocations of inv(16)/t(16;16) are very rare and whether they are also associated with a favorable prognosis is unknown. We report a patient presenting with typical AML-M4Eo and a three-way translocation of inv(16) involving 16p13, 16q22, and 3q22. FISH studies on bone marrow (BM) chromosomes using CBFB and MYH11 DNA probes revealed a fusion of CBFB and MYH11 on 16q of the der(16), as well as a signal from MYH11 on 16p but not from CBFB; normal signals for both probes were present on the normal 16. Neither of these labeled probes was on the der(3), but the translocation between the der(3) and der(16) was confirmed by using a chromosome 16 painting probe. Molecular analysis of BM cells using RT-PCR identified a CBFB-MYH11 fusion transcript type D. After achieving complete remission, the patient relapsed. We conclude that FISH and PCR are feasible tools to distinguish cases with variant abnormalities of inv(16) from cases with other chromosome 16 abnormalities. Variant abnormaties of inv(16) may be not associated with favorable prognosis.