T‐cell acute lymphoblastic leukaemia with late developing Philadelphia chromosome

Summary A case of childhood T‐cell acute lymphoblastic leukaemia (ALL) is presented in which the only chromosome abnormality at diagnosis was a deletion of part of the short arm of one chromosome 9 (9p⁻). Cytogenetic studies at relapse showed, in addition to 9p⁻, a partial deletion of the long arm of one chromosome 6 (6q⁻) and the Philadelphia chromosome (Ph¹) produced as a result of the classical translocation t(9q⁺;22q⁻). All metaphases from haemopoietic colonies grown from a cryopreserved specimen of this patient's marrow at relapse were normal, in contrast to haemopoietic colonies cultured from patients with chronic myelogenous leukaemia (CML) which contained the Ph¹. A hypothesis which incorporates T‐cell ALL with late development of the Ph¹ into the overall family of Ph¹ positive diseases is suggested.