Lack of Prognostic Significance of Absolute Lymphocyte Count After Intensive Induction Therapy in Childhood Acute Lymphoblastic Leukemia

Previous work has shown that the function and number of lymphocytes are vital for the patient's immune system to mount an effective response against cancer cells. Multiple recent studies have demonstrated the prognostic value of absolute lymphocyte count (ALC) in a wide range of malignancies. In children with acute lymphoblastic leukemia (ALL), ALC during induction chemotherapy have been shown to be an independent predictor of adverse outcome, even in the era of minimal residual disease (MRD). Most of the previous studies used Children Oncology Group (COG) based regimens with 3 or 4 drugs induction. We hypothesized that with more intensive induction regimens with 5 or 7 drugs, ALC would lose its prognostic value due to more intensive chemotherapy induced leukopenia.

We reviewed 136 Jordanian pediatric patients (Arabic ethnicity) with newly diagnosed ALL, age 1–18 years, from 2007 to 2009. The patients were treated at a single institution on modified St. Jude total XIII and VX protocols, with a median follow up of 35 months (range: 2–54 months). The induction phase was composed of 7 drugs regimen. Variables analyzed included ALC at diagnosis, day15, day 36 end of induction chemotherapy and at time of post induction marrow recovery, white blood cells at diagnosis, age at diagnosis, gender, immunophenotype, cytogenetics, risk group and MRD status at end of induction. ALC at each time-point was evaluated for prognostic ability by univariate and multivariate analysis.

We found that ALC at day15, day 36 end of induction chemotherapy and at time of post induction marrow recovery failed to have any prognostic effect on event-free survival (EFS) or overall survival (OS). We analyzed ALC as continuous and dichomatous variable, but without any prognostic significance. In contrast to our hypothesis, children with ALL intensive induction regimen did not have profound lymphopenia, with ALC day15 median of 1260 cells/ml (range: 0–9450), ALC day36 median of 866 (range: 100–3476), and ALC (post induction marrow recovery) median of 1145 cells/ml (range: 85–9676). Our cohort confirmed several known prognostic factors in childhhod ALL. For EFS outcome we found MRD35, age, phenotype and risk group to have a significant prognostic effect with P values of (0.016, 0.005, 0.006, 0.001) respectively. For OS outcome we found both age and phenotype to have a significant prognostic P value of (0.006 and <0.001) respectively.

In this study we failed to replicate the previous work that showed the independent prognostic value of ALC during induction therapy in childhood ALL. In contrast to our hypothesis, the reason for the lack of significance was not due to more profound lymphopenia. The lack of ALC prognostic significance in our cohort could be protocol related or patient population (ethnicity) related. Further studies are needed in children with ALL with different ethnic backgrounds to validate the previous work regarding ALC significance before its incorporation in ALL prognostic models, especially in middle or low income countries.

No relevant conflicts of interest to declare.