1. A method of determining whether a solid tumor has an ALL-1 gene rearrangement comprising the steps of: obtaining a sample of a solid tumor; contacting a probe or primer which comprises from at least 20 nucleotides to the full length of ALL-1 cDNA or genomic sequence with nucleic acid from a cell in said sample: and detecting the presence of an ALL-1 gene rearrangement in a cell in said sample.