APL is a monoclonal or oligoclonal disease.

Genomic DNA was prepared from leukemic mice (L1-L4, lanes 1, 3, 5, and 6) or from mice with secondary leukemias derived from reinjection of spleen cells from L1-L2 mice (lanes 2, 4). Samples were digested withHindIII, and then analyzed by Southern blot assay using the PML-RAR cDNA as a probe. (B) FISH analysis (using the proviral sequence as a probe) of metaphase-enriched nuclei of cells derived from the case “L1.” Arrowheads highlight the hybridization signals. Original magnification × 630.