Low spontaneous apoptosis index at diagnosis predicts a high-risk phenotype in paediatric acute lymphoblastic leukaemia.

Background & objectives: Significance of apoptosis as a prognostic marker is less well studied in paediatric acute lymphoblastic leukaemia (ALL) cases. Hence, a prospective study, involving 30 paediatric ALL cases, was done to assess the clinical relevance of in vivo apoptosis.

Methods: Peripheral blood mononuclear cells from all patients were subjected to annexin V/propidium iodide staining to detect the degree of apoptosis [apoptotic index (AI)] at day 0 and day 35 post-induction chemotherapy. In addition, Bax and Bcl2 apoptotic protein expressions were studied at day 0 and their relative fluorescence mean intensity (RFMI) ratios were calculated.

Results: Mean age of patients was 5.1 years. Of the 30 cases, 21 (70%) were at standard-risk, five (17%) at intermediate and four (13%) at high risk. Majority (83%) were B-ALL. Day 8 absolute blast count was >1000/μl in seven (23%) and <1000/μl in 23 of 30 (77%) cases. Day 35 marrow was M1 in 23 (92%) and M2 in two of 25 (8%) cases. AI at day 0 and day 35 ranged from 0.9 to16.6 per cent and 1.4 to 62.8 per cent with a mean of 5.90 and 19.64 per cent, respectively. The Bax/Bcl2 ratio ranged from 0.2 to 3.5 with a mean of 0.83. The ratio was predominantly anti-apoptotic, i.e. <1 (77%). A significant association was noted between low AI at day 0 and high total leucocyte count (P=0.02), T-cell phenotype (P=0.043) and high-risk as per NCI category (P=0.025). Significant increase (>30%) in day 35 AI was seen in only six cases.

Interpretation & conclusions: Our study showed that low AI at day 0 was associated with a high-risk clinical phenotype in paediatric ALL. However, studies on larger group, especially with longer follow up or study of relapse cases, will help draw conclusions regarding apoptosis assessment in paediatric ALL.