FISH IDENTIFIES INV(16)(P13Q22) MASKED BY TRANSLOCATIONS IN 3 CASES OF ACUTE MYELOID-LEUKEMIA

The inv(lb)(p13q22) masked by different translocations was detected by fluorescence in situ hybridization (FISH) and confirmed by molecular analysis in three adult patients presenting with acute myeloid leukemi a (AML)-M2 (cases I and 3) and M4Eo (case 2). Cytogenetic analysis rev ealed 47,XX,t(9;16)(p23;p13),+22 (case I); 46,XX,t(1;16)(p32;p13) (cas e 2); and 46,XY,?del(16)(q22) (case 3). Using a panel of probes for ch romosomes 1, 9, 16, and 20 as well as probes to detect inv(16), i.e., two cosmid contigs hybridizing proximally and distally to the 16p13 br eakpoint, FISH demonstrated inv(16) involving the derivative 16 as wel l as reciprocal translocations between 16q22-qter and 9p24 (case I), 1 p32 (case 2), and 20q13 (case 3). In addition, a small interstitial de l(16)(p13p13) proximal to the MYH11 breakpoint was detected in case I. Reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot analysis showed a CBFB-MYH11 fusion transcript and MYH11 rearran gement, respectively, in all three cases. We conclude that: I) inv(16) can be masked by other structural abnormalities involving chromosome 16; 2) some of the so-called variant translocations not explored at th e molecular level may in fact represent a masked inv(16); and 3) FISH, RT-PCR, and Southern blot analyses are reliable tools to detect maske d inv(16) and should be applied in all AML cases with structural chang es of chromosome 16. (C) 1998 Wiley-Liss, Inc.