Test Details: FISH is one of the most powerful and widely used prognostic tools in patients with CLL even though it evaluates a small number of genetic defects. A deletion of chromosome band 13q14 (13q-) detected by fluorescence in situ hybridization (FISH) analysis is the single most common cytogenetic abnormality in patients with chronic lymphocytic leukaemia (CLL) and has historically been associated with good prognosis. Deletion of 11q,13q,17p and trisomy 12 have a known prognostic value and play an important role in CLL pathogenesis and evolution, determining patient's outcome and therapeutic strategies. The presence of del(11q) implies clinically progressive disease in almost all cases. Patients with 17p deletion have always been included into the highest risk prognostic category, showing the shortest overall survival and disease free survival among all genetic aberrations.