[Philadelphia chromosome-positive acute lymphoblastic leukemia showing normal karyotype at presentation]

21-year-old male was diagnosed as having acute lymphoblastic leukemia (ALL) in March 2001. Standard G-banding analysis revealed normal karyotype. He achieved complete remission after the first course of induction therapy and underwent allogeneic PBSCT in August 2001. However, leukemic cells appeared in the peripheral blood demonstrating complex chromosomal abnormalities with Philadelphia chromosome (Ph1) and expressing minor BCR/ABL transcripts. We thus retrospectively examined the bone marrow sample at presentation with both interphase FISH and RT-PCR methods. Surprisingly, almost all leukemic blasts at presentation turned out to possess the minor type of BCR/ABL fusion gene. In spite of the second allogeneic PBSCT, the patient died of pneumonia and graft-versus-host disease in the liver in September 2002. This case is rare in that cytogenetic analysis failed to detect Ph1 due to leukemic cells dormancy. The application of both FISH and RT-PCR studies would appear to be essential to avoid overlooking Ph1-positive ALL.