Test Details: Acute lymphoblastic leukaemia (ALL) is the most common malignancy of childhood. The presence or absence of a characteristic genetic abnormality usually observed in childhood ALL plays a very important role in determining the prognosis and stratification for treatment. Intrachromosomal amplification of chromosome 21 (iAMP21) is an uncommon high-risk chromosomal abnormality that can occur only in 2% of childhood B-cell precursor lymphoblastic leukaemia. Fluorescence In Situ Hybridization (FISH) analysis using the ETV6/RUNX1 probe allows the identification of a rare chromosome abnormality with important prognostic impact, the iAMP21. iAMP21 has been associated with poor prognosis.