Overview of clinical and genetic features of CML patients with variant Philadelphia translocations involving chromosome 7: A case series

Variant Philadelphia (Ph) translocations involving chromosome 7 are rarely seen in Chronic Myeloid Leukemia (CML) patients. It is aimed to contribute new cases to the literature by reviewing the cases in our archive and shed light into the understanding of the role of chromosome 7 in CML. This study was carried out in 237 newly diagnosed CML patients with variant Ph translocations. Among the patients, those with variant Ph translocation involving chromosome 7 were evaluated in terms of clinical and genetic characteristics. Chromosome analysis was performed on 24 and 48 h of bone marrow cultures. FISH analysis was performed with BCR-ABL1 dual color dual fusion translocation probes. BCR-ABL1 transcript levels were analysed by QRT-PCR and results were reported as BCR-ABL1/ABL1 (BCR-ABL1 (IS) %) according to international scale. Four of the patients had variant Ph translocations including chromosome 7. The karyotypes were 46,XX,t(7;9;22)(p13;q34;q11); 46,XX,t(7;9;22)(p21;q34;q11); 46,XX,t(7;9;22)(q22;q34;q11) and 46,XY,t(7;9;22)(q22;q34;q11). The breakpoints demonstrated by cytogenetic analysis were confirmed by FISH analysis. Monitoring by QRT-PCR showed that patients with variant Ph translocation including 7p13 and 7p21 had a dramatic decrease in BCR-ABL1 levels resulting in complete hematological, complete cytogenetic and deep molecular responses. Despite achieving complete hematological, complete cytogenetic response in two patients with variant Philadelphia translocation, including 7q22, no major molecular response was achieved and both patients are still in the warning category. Response to tyrosine kinase inhibitor therapy may be associated with both the variant translocation mechanism and new gene interactions that occur due to the breakpoints of additional chromosomes involved in translocation.