HOXA-based subclustering of t(4;11)-positive infant ALL samples. (A) Heatmap visualizing 2 clusters among t(4;11)-positive infant ALL samples (n = 29) based on the present or absent of HOXA9, HOXA10, HOXA7, HOXA5, and HOXA3 expression (upper panel). Apart from the 6 probe sets initially separating both patient groups, and additional 31 probe sets (lower panel) appeared to be significantly (FDR < 0.01) differentially expressed between HOXA-negative (n = 16) and HOXA-positive (n = 13) t(4;11)-positive infant ALL. (B) HOXA9, HOXA10, HOXA7, HOXA5, and HOXA3 expression as determined by quantitative reverse-transcribed PCR analyses in t(4;11)-positive infant ALL samples characterized by high (n = 5) or low (n = 5) HOXA expression according to the microarray data. (C) Relapse-free survival curves for HOXA-negative (n = 12) and HOXA-positive (n = 11) t(4;11)-positive infant ALL patients, demonstrating a significantly higher relapse incidence in t(4;11)-positive infant ALL patients lacking HOXA expression (P = .034). Because of a lack of data availability or exclusion of patients who died before entering the INTERFANT-99 treatment protocol, relapse-free survival could only be plotted for 23 of the 29 t(4;11)-positive infant ALL cases.