Objectifs. L’objectif principal de cette étude est d’évaluer l’influence du groupe pronostique auquel le patient est attribué au moment du diagnostic et du protocole de traitement sur le développement d’anomalies dentaires et leur sévérité chez les enfants traités pour la leucémie aigüe lymphoblastique (LAL). L’étude comporte un objectif secondaire : confirmer les résultats des études précédentes ayant montré un nombre et une sévérité plus élevée d'anomalies dentaires chez le groupe 0-5 ans. Hypothèse. Chez des enfants ayant été traités pour la LAL, la prévalence et la sévérité des anomalies dentaires seront plus élevées chez ceux ayant fait partie du groupe pronostique de très haut risque, ayant reçu une combinaison de chimiothérapie, de radiothérapie et de greffe de moelle osseuse et ayant eu leur diagnostic avant l’âge de 6 ans. Méthodes. Des patients âgés entre 14 et 25 ans et ayant reçu un diagnostic de LAL avant l’âge de 11 ans ont été recrutés au Centre Hospitalier Universitaire Sainte-Justine. Un examen dentaire et radiologique ont été effectués. Des données concernant le diagnostic, le groupe pronostique et le type de traitement reçu ont été notées à partir du dossier médical des participants. Résultats. Des défauts dentaires ont été observés chez 26 (50,98%) des 51 sujets, la microdontie étant l’anomalie la plus prévalente (39,22%). Les participants des catégories haut risque et très haut risque ayant reçu de la chimiothérapie haute dose étaient significativement plus à risque de présenter une anomalie dentaire comparé à ceux de la catégorie risque standard ayant reçu la chimiothérapie conventionnelle (p=0.046). Un âge ≤ 5 ans au diagnostic augmentait significativement la prévalence et la sévérité des anomalies dentaires (p<0.001). Conclusion. Le traitement de la LAL pédiatrique affecte l’odontogénèse. Le groupe pronostique et le protocole de traitement ont augmenté le risque de développer au moins une anomalie dentaire. L’âge au diagnostic a affecté la prévalence et la sévérité des anomalies dentaires. / Objective. The main objective of this study is to assess the influence of the risk group to which the patient is assigned at diagnosis and the treatment protocol on the development and severity of dental anomalies in children treated for acute lymphoblastic leukemia (ALL). The secondary aim was to confirm the results of previous studies that showed an increased number and severity of dental defects in children aged 0 to 5 years old at diagnosis. Hypothesis. In children treated for ALL, the prevalence and severity of dental anomalies will be the highest in those who were in the very high risk prognostic group, who received a combination of chemotherapy, total body irradiation and hematopoietic stem cell transplantation and who were diagnosed before the age of 6 years old. Methods. Patients aged between 14 and 25 years old who received diagnosis of ALL before the age of 11 years were recruited at the Sainte-Justine Mother and Child University Hospital Center. Dental and radiographic examinations were performed. Data about the diagnosis, risk group and type of treatment received were collected from medical records. Results. Dental anomalies were recorded in 26 (50.98%) out of 51 subjects and microdontia was the most prevalent dental defect (39.22%). Participants in the high risk and very high risk categories receiving high-dose chemotherapy were significantly more likely to show a dental anomaly compared to those in the standard risk group receiving conventional chemotherapy (p=0.046). Age ≤5 years at diagnosis significantly increased the prevalence of dental anomalies and the severity rating (p<0.001). Conclusion. Therapy for childhood ALL affects the developing dentition. Risk group and treatment protocol influenced the odds of developing at least one dental anomaly. Age at diagnosis affected both the prevalence and severity of dental defects.

O câncer e o processo de hospitalização comumente cursam com forte impacto psicológico sobre as crianças e adolescentes, gerando estresse e fadiga. Isto aplica-se especialmente, para àqueles sob quimioterapia, pois esta, constitui-se em uma das experiências mais estressantes e ameaçadoras que pode exacerbar os sintomas relacionados ao câncer e levar a uma diminuição da qualidade de vida (QV). O estresse associado ao desenvolvimento do câncer pode causar disrupturas no eixo hipotálamo-hipófise-adrenal, e suprimir importantes vias neuroimunoendócrinas. Assim, intervenções destinadas a atenuar as alterações fisiológicas relacionadas ao estresse podem favorecer a recuperação do sistema imune e induzir alterações neuroimunoendócrinas para potencializar a vigilância imunológica durante o tratamento oncológico. Com o aumento da incidência de câncer, é crucial que os profissionais de saúde desenvolvam intervenções eficazes para o manejo dos sintomas oncológicos, de modo a aliviar a sobrecarga do tratamento nesses pacientes durante o processo de hospitalização, de modo a contribuir para um melhor prognóstico da doença. Ademais, pacientes pediátricos oncológicos podem se beneficiar de intervenções não-farmacológicas, por exemplo, a intervenção dos clowns, para aliviar os sintomas relacionados ao câncer. Contudo, poucos estudos têm investigado os mecanismos moleculares envolvendo a intervenção dos clowns. Nosso objetivo principal foi investigar os efeitos da intervenção dos clowns sobre o estresse psicológico e a fadiga-relacionada ao câncer (FRC) em pacientes pediátricos oncológicos sob quimioterapia. Além disso, nós investigamos se alterações nos níveis de cortisol, ?-amilase (sAA), citocinas e metaloproteinases de matriz (MMP-9) estão associadas com estresse psicológico e com FRC de pacientes pediátricos com osteossarcoma submetidos à intervenção dos clowns. Trata-se de um estudo quase-experimental pré-teste/pós-teste. Foram colhidas oito amostras de saliva em momentos idênticos, isto é, no baseline (pré-intervenção) e no pós-intervenção (+ 1h, + 4h, + 9h e + 13h após o despertar). As concentrações de cortisol salivar, sAA, citocinas e MMP-9 foram mensuradas por ELISA. Dados sociodemográficos e clínicos foram coletados via prontuários médicos, além disso, foram aplicadas a Escala de Estresse Infantil-ESI(TM) e a Escala Multidimensional de Fadiga-PedsQL(TM). Os escores das escalas foram comparados entre o baseline e o pós-intervenção, e também, foram correlacionados com os níveis dos biomarcadores. Para análise dos dados, utilizou-se da estatística descritiva e estatística não paramétrica. Em comparação com as medidas do baseline, observamos que os níveis de estresse psicológico total, bem como os de fadiga geral dos pacientes pediátricos oncológicos, melhoraram significativamente após a intervenção dos clowns ( p= 0.003; p= 0.049, respectivamente). Não houve correlações significativas entre as Áreas sob Curva (AUC) da sAA e do cortisol no baseline e nem no pós-intervenção. Além disso, a intervenção dos clowns reduziu os níveis de IL-1? e de cortisol nos pacientes pediátricos com osteossarcoma. A AUC da IL-1? correlacionou-se positivamente com AUC do cortisol e com a AUC da sAA no pósintervenção. Inversamente, os níveis de IL-6, TNF-?, IL-12p70, IL-10, TGF-? e MMP-9 não mostraram diferenças significativas no pós-intervenção. Em síntese, nossos resultados sugerem que a intervenção dos clowns é uma boa intervenção não-farmacológica para reduzir o estresse psicológico e a FRC em pacientes pediátricos oncológicos sob quimioterapia / Cancer and the hospitalization process often have a psychological impact on the children and adolescents, usually leading to intense stress as well as fatigue. This especially applies to children and adolescents who have been submitted to chemotherapy, since it still constitutes a stressful and threatening experience for them and may exacerbate cancer symptom burden clusters, leading to a decrease in their health related quality of life (QoL). In addition, stress associated with cancer development leads to disturbances/disruption in the hypothalamicpituitary-adrenal (HPA) axis and suppresses important neuroimmunoendocrine pathways. Hence, interventions aimed at attenuating the physiological changes related to stress favor the recovery of the immune system and, consequently, induce alterations in neuroimmunoendocrine factors that increase immunological surveillance during cancer treatment. With the increase in cancer rates, it is crucial that healthcare professionals develop effective interventions to support pediatric cancer patients during the hospitalization process in order to relieve the burden of cancer treatment, which may contribute to a better prognosis of the disease. In an attempt to alleviate some of the cancer-related symptoms, pediatric oncology patients can take advantage of non-pharmacological interventions, including clown intervention, which can be a very advantageous approach to reduce unpleasant symptoms in pediatric cancer patients. However, few studies have investigated the molecular mechanisms that mediate health outcomes of clown intervention. The main purpose of this study was to investigate the effects of the clown intervention on psychological stress and cancer-related fatigue (CRF) in pediatric cancer inpatients undergoing chemotherapy. Also, we aimed to investigate whether changes in the levels of biomarkers, including cortisol, ?-amylase (sAA), cytokines, and matrix metalloproteinase-9 (MMP-9) are associated with psychological stress and CRF levels in pediatric osteosarcoma inpatients following clown intervention. A pretestposttest quasi-experimental study was undertaken with pediatric cancer inpatients. Eight nonfasting saliva samples were collected at identical times upon clown intervention, i.e., at baseline (pre-intervention) and post-intervention (+ 1h, + 4h, + 9h, and + 13h post awakening). Salivary cortisol, sAA, cytokines and MMP-9 concentrations were measured using high sensitivity Enzyme-Linked Immuno Sorbent Assay. Sociodemographic and clinical data, and Child Stress Scale-ESI(TM) and PedsQL(TM) Multidimensional Fatigue Scale were applied and the results were compared at baseline and after the clown intervention, and also correlated with biomarker trajectories. Data analysis was performed using nonparametric statistical tests. In comparison with baseline measurements, the overall psychological stress for pediatric cancer inpatients as well as their perception of fatigue improved upon clown intervention (p= 0.003; p= 0.049, respectively). There were no significant correlations between sAA and cortisol for both Areas Under Curve (AUC) at baseline or at post-intervention. Also, clown intervention reduced IL1? and salivary cortisol levels in pediatric osteosarcoma inpatients. Additionally, AUC for IL1? positively correlated with AUC for cortisol as well as with AUC for sAA at postintervention. In contrast, levels of IL-6, TNF-?, IL-12p70, IL-10, TGF-? and MMP-9 did not show significant differences upon clown intervention. Overall, our results suggest that clown intervention is a good non-pharmacological intervention to reduce psychological stress and CRF in pediatric cancer inpatients undergoing chemotherapy

With the increase in survival for children with cancer, part of the focus of current research is aimed towards evaluating how these children are adapting psychosocially. Neurocognitive deficits have been well established. However, there are multiple facets encompassing quality of life, including general mental health, lifestyles and health behaviors, and academic and cognitive functioning. The relationship between neurocognitive and psychosocial functioning has yet to be thoroughly evaluated. The purpose of this study was to investigate the relationship between neurocognitive and psychosocial functioning in survivors of brain tumors and acute lymphoblastic leukemia. Data was collected from existing archival database comprised of patients of the at Cook Children's Medical Center in Texas. The sample consisted of 177 patients between the ages of 3 and 12 who were at least two years post-diagnosis. Measures used included the NEPSY and the Behavioral Assessment for Children. Statistical analyses included a several one-way analysis of variances, an independent samples t-test, a univariate analysis of variance, a hierarchical multiple regression, and odds ratio analyses. Results indicated survivors treated with neurosurgery alone appear to be less at risk for developing behavior problems than other treatment modalities. Also, brain tumor survivors demonstrate more problematic behaviors than survivors of acute lymphoblastic leukemia. Visuospatial functioning, diagnosis, and type of treatment were found to be predictive variables of behavior problems. Attention, and perhaps language, deficits may predispose children to more problems in their behavior. It is concluded that there are other factors affecting behavior in this population that were not accounted for in this analysis. It is recommended for future studies to research the individual clinical scales of the Behavior Assessment System for Children, obtain information from multiple informants, study this relationship longitudinally, and research additional factors that may be influencing the relationship between neurocognitive and psychosocial functioning. This provides evidence of risk factors that should be monitored as the child returns home and to school.

Le neuroblastome à haut risque est caractérisé par un faible taux de survie (~30%) et des récidives fréquentes, malgré les traitements multimodaux existants. Généralement, les études d’évaluation des médicaments utilisent la culture cellulaire en 2D, mais elle ne reflète pas la biologie tumorale du neuroblastome in situ, incluant les caractéristiques associées à l’hypoxie et la densité cellulaire. En comparaison aux patients, la culture cellulaire conventionnelle semble altérer le phénotype cellulaire du neuroblastome, le transcriptome et l’épigénome qui affecteront, à leur tour, les résultats des études pharmacologiques. Ainsi, un nouveau modèle de culture cellulaire en 3D a été développé avec plusieurs lignées cellulaires de neuroblastome afin d’atteindre une culture de sphéroïdes à long terme (un mois) avec un taux de viabilité convenable. L’hypothèse de recherche est que les changements épigénétiques et transcriptionnels seront induits par l’adaptation en 3D et vont s’amplifier dans le temps lors de la culture en 3D. Ces changements ont été mesurés en 3D dans le temps pour identifier le moment où l’épigénome des sphéroïdes ressemble le plus à celui des patient à haut risque. Le changement de l’expression des régulateurs épigénétiques survient 24 jours après la mise en sphéroïde, ce qui se traduit par une différence dans la sensibilité aux médicaments épigénétiques par rapport à la culture 2D. En conclusion, notre étude nous a permis de dériver des nouveaux modèles de neuroblastome qui sont plus représentatifs des patients d’un point de vue épigénétique et pharmacologique. / High-risk neuroblastoma is characterized by a low survival rate (~30%) and frequent recurrences, despite all the multimodal treatments available to date. Typically, drug evaluation studies use 2D cell culture which does not reflect well the tumor biology of neuroblastoma in situ, including features associated with hypoxia and cell density. Thus, compared to patients data, the conventional 2D cell culture seems to alter the neuroblastoma cell phenotype, transcriptome and epigenome which in turn will affect the results of pharmacological studies. A new 3D cell culture model was developed with several neuroblastoma cell lines to achieve long term spheroid culture (up to one month) with a suitable viability rate. We hypothesized that transcriptional and epigenetic changes will be induced by 3D adaptation and will amplify over time in the cells cultured in 3D. All these changes were measured by Western Blot in 2D, in short term 3D and in long term 3D to identify the timepoint when the epigenome of the spheroids most closely resembles that of the patient. We found that the occurrence of changes in epigenetic regulator expression occurs after 24 days of spheroid culture, resulting in a difference in a drug sensitivity compared to 2D culture. In summary, we developed new neuroblastoma models that are more representative of patient’s epigenome and pharmacological sensitivity.

No description available.

La leucémie aiguë lymphoblastique (LAL) est le cancer pédiatrique le plus fréquent. Plusieurs réarrangements chromosomiques ont été associés à cette maladie, dont la translocation t(12;21), qui est observée dans 25% des cas de LAL de type pré-B. Cette translocation engendre l’expression de la protéine de fusion ETV6-AML1. Toutefois, celle-ci n’est pas suffisante pour initier seule une leucémie, ce qui suggère que des mutations additionnelles sont nécessaires à la transformation oncogénique. Or, on observe que l’allèle non-réarrangé d’ETV6 est perdu dans 75% des cas de t(12;21). Cette délétion entraîne l’inactivation complète du facteur de transcription ETV6 et l’abolition de sa fonction biologique. Puisqu’ETV6 semble jouer un rôle de suppresseur de tumeurs, nous croyons que son inactivation favoriserait le développement de la leucémie via la dérégulation de ses gènes cibles. Ce projet visait donc à identifier de nouvelles cibles transcriptionnelles d’ETV6, afin d’élucider son implication dans la leucémie. Une expérience de RNA-Seq a permis d’identifier plus de 200 gènes dont l’expression est corrélée avec celle d’ETV6 dans des cellules souches hématopoïétiques CD34+. Parmi ceux-ci, plusieurs gènes sont impliqués dans la réponse immunitaire et inflammatoire, la migration cellulaire, l’homéostasie ionique et la signalisation intracellulaire. Nous avons également mis en place une approche d’immunoprécipitation de la chromatine afin d’identifier les régions auxquelles le facteur de transcription ETV6 peut se lier. À l’aide de cette méthode, nous avons démontré une interaction entre ETV6 et SLCO2B1, un gène dont l’expression est également co-régulée avec ETV6. Finalement, notre étude suggère qu’ETV6 contribuerait à la leucémogenèse en dérégulant l’expression de certains gènes ayant des propriétés oncogéniques. / Acute lymphoblastic leukemia (ALL) is the most common childhood cancer. Many chromosomal rearrangements have been identified in leukemia, including the translocation t(12;21), which is observed in approximately 25% of children diagnosed with pre-B ALL. This translocation results in the expression of the ETV6-AML1 chimera. However, the fusion protein ETV6-AML1 is not sufficient to initiate leukemia by itself, suggesting that additional mutations are required to promote oncogenic transformation. Accordingly, the expression of the non-rearranged ETV6 allele is lost in 75% of the t(12;21) cases. This deletion leads to the complete inactivation of ETV6 transcription factor and the abolition of its biological function. Because ETV6 seems to be a tumor suppressor, we believe that its inactivation could promote the development of leukemia through the deregulation of its downstream target genes. This project aimed to identify new transcriptional targets of ETV6, in order to elucidate its role in leukemogenesis. A RNA-Seq experiment has led to the identification of more than 200 genes whose expression is correlated with ETV6 mRNA levels in CD34 + hematopoietic stem cells. Among these, several genes are involved in immune and inflammatory responses, cell migration, ion homeostasis and intracellular signaling. We also implemented a chromatin immunoprecipitation approach to identify the binding sites of ETV6. This approach confirmed an interaction between ETV6 and SLCO2B1 gene, whose expression is also co-regulated with ETV6. This study suggests that ETV6 may contribute to leukemogenesis by deregulating the expression levels of several oncogenes.

L’annonce d’un diagnostic de cancer provoque souvent une forte réaction émotionnelle et un stress important tant chez les adultes que chez les adolescents et leurs parents. Certains d’entre eux cherchant à soulager cette détresse se tournent vers des méthodes alternatives positives de gestion de stress, dans le but d’atténuer les effets psychologiques indésirables du cancer. Les thérapies ciblant à la fois le corps et l’esprit gagnent en popularité dans ces populations. Une avenue prometteuse est la méditation de pleine conscience (MPC), inspirée de la philosophie bouddhiste et adaptée dans le cadre d’interventions thérapeutiques pour améliorer la qualité de vie des patients souffrant de maladies chroniques. À ce jour, des études dans le domaine de la santé ont suggéré que la MPC pouvait avoir des effets bénéfiques sur les symptômes et la gestion de plusieurs maladies chroniques dont le cancer, faisant d’elle une avenue thérapeutique intéressante dans le traitement des effets psychologiques indésirables liés à ces maladies. La recherche émergente en pédiatrie suggère des effets comparables chez les enfants et adolescents. L’objectif de la présente thèse a été de développer un essai clinique randomisé visant à évaluer les effets de la MPC sur la qualité de vie, le sommeil et l’humeur chez des adolescents atteints de cancer, en documentant les étapes d’implantation du projet, les embuches qui ont été rencontrées durant son implantation et les résultats obtenus. La thèse est présentée sous la forme de deux articles scientifiques. Le premier article présente la méthodologie qui avait été planifiée pour ce projet mais qui n’a pu être réalisée en raison d’embuches rencontrées dans la complétion de ce pilote. Ainsi, les étapes préliminaires du développement de ce projet de recherche, en accordant une place prépondérante au manuel d’intervention rédigé à cette fin. La mise en place et la structure de ce projet, nommément le devis méthodologique employé, la taille d’échantillon visée, les méthodes de recrutement mises en place et les stratégies de randomisation prévues, sont décrites en détail dans cet article. Pour les fins de ce projet, un manuel d’intervention de MPC a été rédigé. L’intervention en MPC, menée par deux instructeurs formés en MPC, s’est échelonnée sur une durée de huit semaines, à raison d’une séance d’une heure trente par semaine. Une description détaillée de chaque séance est incluse dans cet article, dans un but de dissémination du protocole de recherche. Des analyses intragroupe serviront à évaluer l’impact de l’intervention en méditation de pleine conscience sur la qualité de vie, le sommeil et l’humeur pré-à-post intervention et au suivi à six mois. Des analyses intergroupes prévues sont décrites afin de comparer les effets de l’intervention entre les participants du groupe contrôle et du groupe expérimental. Les limites potentielles de ce projet, notamment la participation volontaire, le risque d’attrition et la petite taille d’échantillon sont décrites en détail dans cet article. Le deuxième article présente, dans un premier temps, le déroulement du projet de recherche, en mettant en lumière les embuches rencontrées dans son implantation. Ainsi, les leçons à tirer de l’implantation d’un tel essai clinique en milieu hospitalier au Québec sont décrites selon trois axes : 1) les défis liés au recrutement et à la rétention des participants; 2) l’acceptabilité et la compréhensibilité de l’intervention en pleine conscience; et 3) le moment où l’intervention s’est déroulée (timing) et l’impact sur l’engagement requis des participants dans le projet. Durant une période de recrutement de neuf mois, 481 participants potentiels ont été filtrés. 418 (86,9 %) d’entre eux ont été exclus. 63 participants potentiels, vivant à moins d’une heure de Montréal, ont été approchés pour prendre part à ce projet. De ce nombre, seulement 7 participants (1,4%) ont accepté de participer aux rencontres de MPC et de compléter les mesures pré-post intervention. Un bassin d’éligibilité réduit, ainsi que des taux de refus élevés et des conflits d’horaire avec les activités scolaires ont eu un impact considérable sur la taille d’échantillon de ce projet et sur l’absentéisme des participants. Malgré l’intérêt manifeste des équipes médicales pour la recherche psychosociale, les ressources requises pour mener à terme de tels essais cliniques sont trop souvent sous- estimées. Les stratégies de recrutement et de rétention des participants méritent une attention spéciale des chercheurs dans ce domaine. Dans un deuxième temps, le deuxième article de cette thèse a pour objectif de présenter les résultats de l’intervention en MPC chez des jeunes ayant le cancer, en examinant spécifiquement l’impact de l’intervention sur la qualité de vie, le sommeil et l’humeur des jeunes pré-post intervention et lors du suivi à six mois. Faisant écho aux embuches décrites préalablement décrites, les analyses statistiques n’ont permis de déceler aucun effet statistiquement significatif de notre intervention. Aucune différence significative n’est notée entre les participants du groupe expérimental et les participants du groupe contrôle. Les difficultés rencontrées dans de la complétion des devoirs et de la pratique de techniques de méditation entre les séances, décrites en détail cet article, expliquent en partie ces résultats. Globalement, le contexte développemental spécifique à l’adolescence, ayant possiblement eu un impact sur l’adhérence des participants à la thérapie proposée et à leur motivation à prendre part aux rencontres, les scores sous-cliniques lors du premier temps de mesure, l’impact du soutien social inhérent au contexte de thérapie de groupe, ainsi que les caractéristiques personnelles des thérapeutes, pourraient avoir influencé les résultats de ce pilote. Les résultats de ce projet pilote nous laissent croire que la prudence est de mise dans la généralisation des bienfaits et de l’efficacité de la pleine conscience observés chez les adultes atteints de cancer dans son application aux adolescents en oncologie. En conclusion, la présente thèse contribue à enrichir la recherche dans le domaine de la MPC chez les jeunes en questionnant néanmoins la pertinence d’une telle intervention auprès d’une population d’adolescents souffrant de cancer. Ainsi, il convient d’analyser les résultats obtenus en tenant compte des limites méthodologiques de ce projet et de poser un regard critique sur la faisabilité et la reproductibilité d’un projet d’une telle envergure auprès d’une même population. Les leçons tirées de l’implantation d’un tel projet en milieu hospitalier pédiatrique se sont avérées d’une importance centrale dans sa complétion et feront partie intégrante de toute tentative de réplication. D’autres essais cliniques de cette nature seront inévitablement requis afin de statuer sur l’efficacité de la MPC chez des adolescents atteints cancer et sur la faisabilité de l’implantation de cette méthode d’intervention auprès d’une population pédiatrique hospitalière. / News of a cancer diagnosis often elicits a strong emotional reaction in teenagers and their parents. To address these emotional challenges, various psychosocial approaches have been developed, including mind-body therapies. Mindfulness-based meditation, inspired from the Buddhist tradition, and adapted to improve quality of life in patients suffering from chronic illnesses, constitutes a promising option. Altogether, authors have suggested that mindfulness meditation could have beneficial effects on physical and psychological symptoms among adults with different chronic illnesses, namely cancer, and could hence be an interesting therapeutic avenue in the treatment of these conditions. The emerging research in pediatrics is suggesting similar effects in children and adolescents. The goal of this thesis was to develop a randomized clinical trial with the aim to evaluate the effects of a mindfulness- based intervention on quality of life, sleep and mood in adolescents with cancer, while documenting lessons learned from this experience and obtained results. This thesis is comprised of two scientific articles. The first article presents the initial study protocol that was planned for this study, although this could not be implemented because of multiple feasibility challenges that were met along the way. Preliminary steps in developing this research project, giving prominence to its intervention manual. The structure of the project, namely the choice of design and participant flow, the targeted sample size, along with recruitment and randomization strategies, are described in this article. For the purposes of this project, an intervention manual was written. The mindfulness-based intervention, given by two trained instructors, comprised of eight weekly sessions, lasting 90 minutes each. A detailed description of each weekly session was included in this article, in order to foster the dissemination of our research protocol. The second article is firstly based on our experience of carrying out a mindfulness- based clinical trial with a group of teenagers treated for cancer. While the initial goal of the trial was to expand the field of mindfulness research of youth with cancer, it became clear that much was to be learned from the challenges we met along the way. The goal of this article was therefore to document lessons learned from completing this trial to improve feasibility of future similar trials. Our findings are described in terms of the challenges encountered according to the following three categories: 1) recruitment and retention challenges; 2) treatment acceptability; 3) timing and commitment. Over 9 months of recruitment, 481 youth were screened for participation in the present project. Of these, 418 (86,9 %) were excluded. Of the 63 that were approached, only 7 (1,4%) agreed to participate in the project, gave consent and provided a complete dataset. A narrow pool of eligible participants, along with high refusal rates, scheduling conflicts with school and absenteeism had a significant impact on sample size in this project. Although there is manifest interest from the medical care community and scientific merit to conducting clinical trials, the resources needed for implementing these types of projects are often underestimated. Effective recruitment and retention merits particular attention. Secondly, this article presents results of our mindfulness-based intervention in adolescents with cancer, specifically in terms of quality of life, sleep and mood. Participants from the experimental group completed follow-up measures. Testing revealed no significant differences on any variable between participants from the experimental group and participants from the control group pre-to-post assessment. This could be explained by a lack of exposure to mindfulness techniques following the eight weeks program, limiting the generalization potential beyond therapy sessions. Moreover, encountered difficulties with homework, previously mentioned, could explain the absence of a mindfulness skills acquisition. Globally, our results could be explained by the inherent developmental changes of adolescence, impacting participants’ openness and adherence to mindfulness. Sub-clinical psychological symptoms could also strongly impact the usefulness of mindfulness meditation in youth with cancer. Data from this pilot study suggests that caution is required in generalizing the results used to determine the effectiveness of mindfulness interventions in adults with cancer, as they are not a guarantee of success and effectiveness for adolescent oncology populations. In conclusion, the present thesis helps advance the state of knowledge in mindfulness and youth research, namely by presenting data that questions the relevance of mindfulness interventions for teenagers with cancer. It is necessary to be cautious in analysing results from this thesis, especially when taking into consideration the methodological limitations that were faced in its completion and their impact on feasibility and reproducibility of such a project on a larger scale. Thus, lessons learned from the implementation of a mindfulness intervention project in pediatric oncology were of crucial importance in the completion of this project and will be an essential part of any attempt to replicate a project of this nature. Further research in this field will be necessary to conclude whether mindfulness interventions are beneficial for teenagers with cancer and whether they are feasible with pediatric populations.

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No description available.

No description available.