T-cell acute lymphoblastic leukaemia with late developing Philadelphia chromosome.

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.