Marked basophilia in acute promyelocytic leukaemia treated with all-trans retinoic acid: molecular analysis of the cell origin of the basophils.

We report a patient with acute promyelocytic leukaemia who developed marked basophilia during all-trans retinoic acid treatment. We studied genomic DNA and RNA extracted from the patient's peripheral leucocytes in order to determine the origin of the basophils. The RAR alpha rearranged band in the Southern blot analysis and a chimaeric product of PML-RAR alpha by polymerase chain reaction were strongly visible before ATRA treatment, but at the time of maximal basophilia both of them were markedly diminished. These findings suggest that the basophils which appeared during the ATRA treatment are reactive in nature rather than a leukaemic clone.