Trisomy 8 in acute promyelocytic leukaemia: an interphase study by fluorescence in situ hybridization


Dr Y. L. Kwong, University Department of Medicine, Professorial Block, Queen Mary Hospital, Pokfulam Road, Hong Kong.


Summary. Acute promyelocytic leukaemia (APL) is characterized by t(15;17)(q24;q21). Trisomy 8 is the commonest accompanying karyotypic aberration. We investigated 14 APL patients for trisomy 8 using fluorescence in situ hybridization (FISH). Conventional cytogenetic analysis showed trisomy 8 in two of nine successfully karyotyped cases. With FISH, a possible third case showing a subclone (1-2-5%) with trisomy 8 was found. The trisomy 8 clone size defined by karyotyping and FISH was concordant in one case and discordant in another, in which trisomy 8 was found in 100% of metaphases but only in 48% of leukaemic prbmyelocytes by FISH. Therefore trisomy 8 was mosaic in all the cases, suggesting that it had arisen from clonal evolution. AU-trans-retinoic acid successfully induced morphologic remission in both cases with trisomy 8.