Test Details: 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). 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. Deletion of 13q14 region, found in more than 50% of the CLL patients, is the most common cytogenetic abnormality detected by FISH and has historically been associated with good prognosis. Trisomy 12 has been considered as an immediate risk marker. 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.