Trisomy 8 is relatively specific for myeloid disorders and is rarely observed in lymphoid disease. It is found in 10-15% of patients with acute myeloid leukemia (AML), 15-20% of patients with myelodysplastic syndromes (MDS), as a secondary abnormality in Philadelphia chromosome positive CML, and in other myeloproliferative disorders. Trisomy 8 occurs as the sole chromosome abnormality in about 40% of AML cases, occurs in combination with simple chromosome changes in 35% of cases, and as part of a complex karyotype in 25% of AML patients.