The translocation t(1;19)(q23;p13) (TCF3/PBX1 fusion) is the most common recurrent genetic abnormality detected amongst patients with B-cell lymphoblastic leukaemia in Johannesburg, South Africa

Background: B-cell lymphoblastic leukaemia (B-ALL) is a malignancy of immature B-cells with several described recurrent genetic abnormalities. These have distinct clinico-pathological associations and show regional variation in prevalence. In all previously reported series, the translocation t(1;19) is uncommon, comprising < 10% of all cases. The genetic composition of B-ALL in Africa is unknown. Aim: The aim of this study was to assess the genetic landscape of B-ALL in Johannesburg, South Africa. Setting: The Johannesburg state-sector. Methods: All cases of B-ALL diagnosed by flow cytometry in the state-sector hospitals of Johannesburg over 36 months between 2016 and 2019 were identified and pertinent data were recorded from the laboratory information system. Results: A total of 108 patients with B-ALL were identified, 82 (75.9%) of whom were children or adolescents. The translocation t(1;19)(q23;p13) was the most common genetic abnormality identified (23.7% of cases), predominating in young patients. The translocation t(9;22)(q34;q11) was the next most common aberration (17.5%) occurring predominantly in adults > 40 years of age, but also in 8.1% of children. Crude survival rates were overall poor (44.6% overall and 57.4% in patients < 18 years of age). On survival analysis, older age, KMT2A-rearrangement and t(1;19) were independently associated with relapse-related death. The t(9;22) was not associated with mortality independently from age. Conclusion: B-ALL shows a distinct pattern of lymphoblastic leukaemia-associated chromosomal translocations in Johannesburg.