Predictive Role of Flow Cytometry in Assessing Very Early Treatment Response in Childhood ALL.

Acute lymphoblastic leukaemia is the most common childhood malignancy. In the modern treatment of acute leukaemia, advances in supportive care have allowed the intensification of therapy, and survival rates have risen accordingly. Cure rates in childhood acute lymphoblastic leukaemia (ALL) have increased from 10% to 80% over the last four decades. Currently clinical parameters such as white blood cell count and age at diagnosis are used for treatment stratification. This stratification aims to maximise the efficacy and minimize the toxicity of treatment, with the intensity of treatment being adjusted according to the risk of relapse. Unfortunately, the clinical and biologic parameters most commonly used for risk classification fail to identify all patients who relapse, with most patients who relapse falling into the ‘low risk’ group. In addition other patients who are actually at low risk of relapse may receive more intensive treatment than is necessary. Morphology is used to assess very early response at day 8/15, but lacks specificity and sensitivity. Many publications have reported marked variability in indivual reports of morphological blast %. Better techniques of assessing very early response are therefore needed. Detection of minimal residual disease (MRD) allows better estimation of the leukaemic burden and can help selection of appropriate therapeutic strategies. Flow cytometric (FC) detection of MRD is based on the identification of immunophenotypic combinations expressed on leukaemic cells but not on normal hematopoietic cells - leukaemia associated immunophenotypes (LAIPs). FC analysis is an attractive option as it is quick and more specific. We prospectively analysed bone marrow samples from 70 patients who presented with ALL to our unit between 1999–2003 and attained morphological remission. These patients were treated on a standard protocol. Multiparameter FC identification of LAIPs was performed at various time points, as dictated by the treatment protocol. We looked at the predictive value of FC at d8/15 on treatment, at different levels of MRD. Our results showed that amongst children with flow MRD< 0.01% (n=5) on day 8/15 of chemotherapy, there were no relapses. Perhaps this cohort of patients could receive less intensive chemotherapy to minimise long-term side effects. The second group was children with flow MRD between 0.01%– 1%(n=33). In this group we saw 14% relapses. The third group was children with flow MRD between 1–10% (n=20), in which we observed 25% relapses. The fourth group was children with flow MRD > 10%, (n=12). 40% of this group suffered relapses. It appears that as early as day 8/15 of treatment, we can identify patients who are at very high risk of relapse, and perhaps these children need intensification of chemotherapy early on or some other novel intervention eg stem cell transplantation. FC appears to offer the ability to identify very early in treatment those at high risk of relapse and those with a high chance of cure. Treatment may therefore be stratified according to these risks with the aim of improving cure rates. These results need to be confirmed in a larger cohort of patients but these preliminary results are very promising in the risk stratification of childhood ALL.