Problèmes de comportement à long terme chez les patients pédiatriques atteints de leucémie lymphoblastique aiguë

Recent improvements in pediatric cancers treatment have led to marked increases in patient survival rate. However, it has been well documented that pediatric cancer survivors are at elevated risk for various other health problems. With respect specifically to neuropsychological side effects, known predictors (mainly: age at diagnosis, patient gender, exposure to radiation therapy) remain insufficient so far to target, and prevent efficiently, long term sequelae in this population.   General objectives related to this thesis were: 1) characterization of individual trajectories of behavioral problems in pediatric patients with acute lymphoblastic leukemia; 2) the identification of genetic, medical and psychosocial determinants of behavioral problems in this population.   This research program was based on the following hypotheses: 1) there is an association between the trajectories of individual behavioral problems and a – familial well-being-related psychosocial factors, b – gene polymorphisms involved in the therapeutic responses to methotrexate and glucocorticoids, c – anti-cancer treatments-related variables. 2) Multilevel statistical modeling can be used to characterize patient groups according to their individual behavioral problem trajectories, and can also identify predictive factors.   138 pediatric patients (0-18 years old) who received an acute lymphoblastic leukemia diagnosis between 1993 and 1999 at CHU Ste-Justine participated in this 4 years-long longitudinal study. A standardized and validated instrument, the Child Behavior Checklist, was used to measure behavior problems, as reported by the mother, at diagnosis, and then 1, 2, 3 and 4 years post-diagnosis. Genetic, psychosocial and medical data were also collected during this longitudinal study; these data were exploited in the context of the statistical modeling performed.   Results obtained suggest that internalized and externalized behavioral problems have distinct trajectories and have different predictive factors. Internalized problems are affective issues presented by the patient, such as depressive or anxious symptoms. They are highly prevalent post-diagnosis and normalize over the following years, suggestive of temporary yet significant problems. Stress-enhancing medical variables such as a higher relapse risk at diagnosis and medical complications requiring a longer hospitalization slow down the normalization process. Externalized problems need interpersonal contact to occur; violence or aggressiveness manifestations are some examples. Compared to internalized problems, externalized problems are much more stable across time. However, pharmacological and genetic variables do contribute to individual differences in trajectories. In particular, administration of a more potent glucocorticoid (from pharmacological and toxicological perspectives) and being homozygous for NOS3 gene -786C844T haplotype are linked to modulation of externalized problems in time. Finally, the level of perceived family stress at time of diagnosis is positively correlated with initial externalized problems, while shortly after the induction period, the level of familial stress is linked with the initial internalized problems.     Together, these results support the idea that a holistic care strategy is essential to develop efficient, preventive interventions in this population, due to the multifactorial nature of these behavioral problems. The knowledge generated in the present studies could contribute to better quality of life for these patients.     This thesis also brings a more holistic contribution to our current knowledge of behavioral problems in this population, by highlighting the need for individual, multidisciplinary follow-ups, with particular emphasis on repeated measurements and appropriate statistical analyses. More than ever, knowledge de-compartmentalization appears essential in reaching a certain comprehension level of observed phenomena, rather than adhering to descriptive settings. It indicates that, despite obvious methodological and logistic challenges, this type of research is not only desirable in studying dynamic processes, but is certainly achievable with current analytical tools.

Keyphrases: NOS3, pediatric oncology, acute lymphoblastic leukemia, psychosocial factors, pharmacogenetics, glucocorticoids, multilevel statistical modeling