The significance of the Philadelphia chromosome in acute lymphoblastic leukaemia: a report of two cases.

Two cases of Philadelphia chromosome (Ph1) positive acute lymphoblastic leukaemia are reported, both of which lost the Philadelphia chromosome during remission. In one patient remission of the acute lymphoblastic leukaemia continued but classical Ph1 positive chronic granulocytic leukaemia developed. In the other patient relapse of the acute lymphoblastic leukaemia occurred associated with the return of the Ph1 chromosome. The evidence suggests that the chromosome aberration occurred in a pluripotential stem cell, which in one case proliferated along both a lymphoid cell line and a myeloid cell line. Both cases responded well to conventional therapy for acute lymphoblastic leukaemia.