Prognostic significance of p16INK4a immunocytochemistry in adult ALL with standard risk karyotype.

The p16INK4a gene is frequently inactivated in acute lymphoblastic leukemia (ALL), by homozygous deletion. However, p16INK4a protein expression also varies widely in ALL blasts. We investigated the p16INK4a protein expression by immunocytochemistry (ICC) analysis in 76 cases adult ALL. We observed a great variation of the percentage of ICC-positive leukemic cells between samples even in which FISH analysis did not find p16INK4a gene deletion. All patients carrying a p16INK4a gene homozygous deletion were also negative by ICC. ALL with negative p16INK4a ICC were more frequently of T lineage, but no significant differences for white blood cell count, presence of bulky disease, karyotype, hemoglobin level, complete remission rate, overall and event-free survival (EFS) were found. However overall survival and EFS were significantly lower in patients negative by ICC, when analysis was performed in ALL with standard risk karyotype. We also analyzed sequentially at diagnosis and relapse nine cases and observed that one case lost p16INK4a expression between diagnosis and relapse, but that on the contrary three other samples showed increased expression at relapse. These findings suggest that p16INK4a ICC and deletion analysis provide distinct information about ALL cells and that the simple ICC method may be of prognostic value in standard risk adult ALL.