Rearrangements of the RAR-alpha gene in acute promyelocytic leukaemia: correlations with morphology and immunophenotype.

We have used genomic probes which specifically recognize DNA rearrangements of the RAR-alpha locus on chromosome 17q21 in patients with acute promyelocytic leukaemia (APL) and acute myeloid leukaemia (AML) subtypes. Molecular data were examined in comparison with morphological and immunophenotypic characterization at diagnosis in 20 hypergranular FAB M3 cases, five microgranular APL (M3v), 51 non-M3 AML and 12 myeloid CML blast crises. Rearrangements of the RAR-alpha locus were only detected in 23/25 APL cases and in none of the other FAB subtypes analysed. Surface marker characterization showed a consistent immunophenotypic profile--HLADR negative, CD9 and CD13/33 positive--in all M3 and M3v cases. Neither HLADR negativity nor CD9 positivity were associated with RAR-alpha rearrangements in non M3 AML. Our data indicate that RAR-alpha gene rearrangements are relevant diagnostic features of both M3 and M3v, and may prove useful molecular marker for follow-up analysis in APL patients.