CLINICAL ASPECTS OF EXPRESSION OF INVERSION-16 CHROMOSOMAL FUSION TRANSCRIPT CBFB MYH11 IN ACUTE MYELOGENOUS LEUKEMIA SUBTYPE M1 WITH ABNORMAL BONE-MARROW EOSINOPHILIA/

The pericentric inversion of chromosome 16 (inv(16)(p12q22)) is a char acteristic karyotypic abnormality associated with acute myeloid leukem ia, most commonly of the M4Eo subtype. It is increasingly appreciated as both a favorable prognostic factor and important guide to therapy. The breakpoints of the inversion have been cloned and a fusion transcr ipt can be identified by RT-PCR. We expand upon our prior abstract of a case of AML subtype MI with abnormal eosinophils that expressed the inversion 16 fusion transcript CBFB/MYH11. During remission, the trans cript could not be detected. The patient relapsed twice during the fir st year after attaining a complete remission. Morphologically, the rel apsed specimens were identical to the appearance of his diagnostic spe cimen. However, the CBFB/MYH11 fusion transcript was not detected in t he relapsed specimen. We conclude that CBFB/MYH11 fusion transcript de tection, as a surrogate for the favorable prognosis and treatment plan ning implied by inv(16) in AML M4Eo, should not be exclusively relied upon in AML M1 in the absence of prospective study of this specific (M 1) category of AML. RT-PCR analysis should be correlated with cytogene tics when available and if used alone should be interpreted cautiously in cases of AML with atypical morphological features.