[Variant Philadelphia chromosome identified by interphase fluorescence in situ hybridization (FISH) without evidence on G-banded karyotyping and metaphase FISH].

A variant Philadelphia chromosome (Ph) is generated from translocation of one or more partner chromosomes in addition to chromosomes 9 and 22. We have described the cases of 2 patients bearing variant Ph detected by interphase FISH but not detected by G-banded karyotyping and metaphase FISH. FISH was performed using BCR/ABL dual color dual fusion translocation probes (Abbott Molecular, USA). A 52-year-old man was diagnosed with acute leukemia of mixed phenotype. G-banded karyotyping showed 46,XY,t(9;22)(q34;q11.2)[12]/47,idem,+der(22)t(9;22)[5]/46,XY[3]. Interphase FISH revealed nuc ish(ABL1,BCR) × 3(ABL1 con BCR × 2)[329/450]/(ABL1,BCR) × 4(ABL1 con BCR × 3)[5/450]/(AL1,BCR) × 3(ABL1 con BCR × 1)[44/450]. Metaphase FISH showed ish (9;22)(ABL1+,BCR1+;BCR+,ABL+)[22]/der(22)(BCR+,ABL1+)[3]. The other case was that of a 31-yr-old male patient diagnosed with CML in the blastic phase. G-banded karyotyping of all 20 metaphase cells showed 47,XYYc,dup(1)(q21q32),del(7)(p11.2),t(9;22)(q34;q11.2). Interphase FISH revealed nuc ish(ABL1,BCR) × 3(ABL1 con BCR × 2)[254/600]/(ABL1,BCR) × 3(ABL1 con BCR × 1)[191/600]. Metaphase FISH showed ish t(9;22)(ABL1+,BCR+;BCR+,ABL1+)[16]. These results suggest that typical t(9;22) and variant Ph may coexist in the same patient, and interphase FISH may facilitate the detection of the variant Ph that cannot be detected by G-banded karyotyping alone.