AbstractWe report here a patient with de novo acute myelocytic leukemia with trilineage myelodysplasia (AML/TMDS) in whom cytogenetic analysis was normal at diagnosis and in whom Philadelphia chromosome (Ph1) with monosomy 7 emerged at the terminal stage of the disease. Reverse transcription polymerse chain reaction (RT‐PCTR) on the Ph1 positive specimen detected the mRNA encoding p190bcr/ab1 was not detected at diagnosis and or at relapse. These observations support the hypothesis that late‐appearing Phl and monosomy 7 might be the result of clonal evolution during the course of leukemia, and p190bcr/abl might play a role in the terminal transformation or progression of leukemia. © 1995 Wiley‐Liss, Inc.