A new minimal deleted region at 11q22.3 reveals the importance of interpretation of diminished FISH signals and the choice of probe for ATM deletion screening in chronic lymphocytic leukemia.

Deletion of ATM detected by fluorescent in situ hybridization (FISH) in chronic lymphocytic leukemia predicts short treatment free survival and poor outcome following alkylator/purine analogue therapy. We describe five cases, with a diminished ATM FISH signal, investigated by TP53 mutation/dysfunction studies and single nucleotide polymorphism (SNP) array. The diminished signal represented loss of the ATM gene, which could have been missed were the cases not further investigated. These rare cases highlight the need for careful consideration of the choice of probe and interpretation of unusual signal patterns in FISH screening. We define a new minimal region of deletion at 11q22.3. Crown