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Variant Ph1 translocations in CML and their incidence, including two cases with sequential lymphoid and myeloid
Abstract:
A serial cytogenetic study of 110 cases of chronic myelogenous leukemia (CML) has been performed with G- and/or Q-banding techniques with the following results. (1) Seven out of the 110 cases were karyotypically normal. (2) A variant Ph1 translocation was observed in three cases. In one case, the leukemic cells contained two reciprocal translocations, i.e., a t(3;9) (q21;q34) and a t(17;22)(q21;q11); therefore, a Ph1 chromosome was masked by a translocation of the deleted material from the 17q onto the band q11 of the long arm of a chromosome No. 22. In the second case, a variant Ph1 translocation involved chromosomes No. 9, 20, and 22, resulting in a karyotype interpreted as 46,XX,t(9q+;20q+;22q-); in this rearrangement, one of the segments, i.e., 9q31 or 9q33, seemed to be interstitially deleted and inserted into the interstitial region (q11) of a chromosome No. 20 and the 22q11 leads to qter was translocated onto the 9q. This is the first case in which chromosome No. 20 was involved in a variant Ph1 translocation. In the third case, the karyotype of leukemic cells was interpreted as 46,XX,t(5;9;22)(q13;q34;q11). (3) The frequency of Ph1-negative CML and that of Ph1-positive CML with various types of Ph1 translocation from 15 studies reported as series of 25 or more cases, including the present study, have been tabulated. The incidence of a variant Ph1 translocation was 4.1% (42/1027 cases of Ph1-positive CML); of the 42, 13 were of a simple type and 29 of a complex type. (4) In one case of the present study, a masked Ph1 by a translocation of material onto the short arm of the 22q- was observed in the blastic crisis but not in the chronic phase. From the present study and a review of the published cases, it appears that the incidence of such a "masked" Ph1, which cannot be detected by conventional Giemsa staining, is less than 0.6% in CML cases. (5) The first and the second cases with a variant Ph1 translocation mentioned above developed a myeloid blastic crisis after the induction of remission of a lymphoid blastic crisis. For the present, it is unclear whether the occurrence of such blast cells in the two cases and the cytogenetic findings are coincidental. However, the evidence supports the notion of "lymphoid-myeloid" multipotentiality of certain leukemic cells.