Since the landmark study published in 2000 by Dohner et al. [6] indicated that 80% of CLL cases could be risk stratified based on the presence of four recurrent chromosomal abnormalities (del(13q), trisomy 12, del(11q)/ATM, and del(17p)/TP53), which could be quickly detected even on non-dividing nuclei via FISH testing, a CLL FISH panel targeting these four loci has been developed and widely applied as the gold standard laboratory test for CLL cases. The gene discussed is ATM; the disease is B-cell chronic lymphocytic leukemia.