CD9 as a Potential Prognostic Biomarker in Paediatric B-Cell Acute Lymphoblastic Leukaemia.

Objective: To evaluate the role of CD9 for predicting ETV6::RUNX1, BCR::ABL1, and KMT2A fusion genes with prognostic significance in B-cell acute lymphoblastic leukaemia (B-ALL).

Study design: An observational study. Place and Duration of the Study: Indus Hospital and Health Network, Karachi, Pakistan, from May 2020 to August 2022.

Methodology: Data of 488 paediatric (B-ALL) children diagnosed by flow cytometry were retrieved. Recurrent genetic abnormalities for BCR::ABL1, ETV6::RUNX1, and KMT2A fusion genes were retrospectively monitored. Fisher's Exact, Pearson's Chi-Square, and Mann-Whitney U tests along with univariate and multivariate analyses were performed.

Results: The frequency of BCR::ABL1 was 9.01% [p = 0.097]. The ETV6::RUNX1 gene rearrangement was observed in 37.0% vs. 52.6% (p = 0.168), and KMT2A gene rearrangement in 8.52% vs. 10.5% (p = 0.690) in CD9+ and CD9- groups, respectively. The potential significance of BCR::ABL1 suggests CD9's role in indicating the presence of this unfavourable genetic marker, while for ETV6::RUNX1, CD9 expression may be linked to a less positive genetic profile. Lymphadenopathy was significant in CD9+ group, while bone marrow blast counts were notable in CD9- group. The survival rates did not significantly differ between the two groups.

Conclusion: CD9 can be used as a surrogate biomarker in predicting disease prognosis by recognising the patients with high-risk factors i.e., lymphadenopathy, elevated white blood cells, possible occurrence of BCR::ABL1, and the scarcity of ETV6::RUNX1 within the CD9+ group.

Key words: Immunophenotyping, Cytogenetics, Gene rearrangement, CD9 expression, Prognostic marker.