OBJECTIVESTo explore whether PML/RAR alpha fusion gene presented in patients with typical clinical characteristics of acute promyelocytic leukemia (APL) but normal karyotype or atypical translocation of chromosomes 15 and 17 by conventional cytogenetic analysis (CCA), and to assess the application of fluorescence in situ hybridization (FISH) to diagnosis of APL.

METHODS193 newly diagnosed APL patients received CCA in our hospital, 32 cases of whom were carried out FISH analysis, and some of the patients received reverse transcriptase polymerase chain reaction (RT-PCR) detection.

RESULTS132 of 193 (68.4%) cases were identified to have t(15;17) (q22;q12) by CCA. The selected 32 patients were divided into three groups according to CAA results: group 1 included 14 cases with typical t(15;17), group 2 included 13 cases without t(15;17), and group 3 included five cases with complex karyotype involving chromosomes 15 and 17. As expected, all cases in group 1 were detected PML/RAR alpha fusion by FISH. In group 2, all patients presented the same molecular abnormality by FISH in spite of absence of t(15;17), and in group 3, FISH not only detected PML/RAR alpha fusion but also identified the fusion signals located on chromosomes, other than chromosome 15q.

CONCLUSIONAll the APL with typical clinical characteristics can be detected PML/RAR alpha fusion by FISH or RT-PCR regardless of classical t(15;17). FISH is more sensitive for molecularly diagnosis of APL, and can identify the precise location of the fusion signals in complex karyotype. It is necessary in clinically APL patients with no or atypical chromosomal abnormalities to perform FISH analysis.