Les résultats des projets actuels apportent une information, sur différents aspects des rôles de la voie PI3K, dans le développement du cancer du sein, et la réponse au traitement. Les projets particuliers couvrent des sujets liés à la voie aux niveaux concernant les récepteurs de la famille HER, activant la voie PI3K, ainsi que PI3K et les effecteurs en découlant. Les effets pronostic et prédictif de la dérégulation de PI3K sont les sujets centraux de la recherche décrite ici. Une baisse d’expression de PI3KR1 est associée à une survie réduite dans notre cohorte de patients. Une attention particulière a été portée aux mutations de PIK3CA communes dans le cancer du sein. Tandis que les mutations de PIK3CA agissent comme des marqueurs de bon pronostic chez les patients anti-HER2-naïfs, ces mutations agissent au contraire comme prédicteurs négatifs de la réponse au traitement par trastuzumab. Les résultats décrits mènent un peu plus vers l’implication de plusieurs voies moléculaires altérées, en particulier la voie de signalisation Wnt, dans la tumorigénèse des cancers du sein PIK3CA mutés. De plus, nous avons testé les taux de lapatinib plasmatique montrant une augmentation pertinente dans les périodes d’état d’équilibre du traitement. Par ailleurs, nous avons démontré des incohérences dans l’évaluation de l’EGFR et proposé des approches pour l’interprétation des comptages d’immunohistochimie et de FISH. Tous ces sujets sont connectés par la 170 voie PI3K, et le besoin d’approfondir les connaissances actuelles, et d’apporter de nouvelles informations utiles applicables dans le futur dans les pratiques cliniques / Results of the presented research projects bring information about several aspects of the PI3K signaling pathway roles in breast cancer development and treatment response. The particular projects covered the subjects connected with the signaling pathway, ranging from the HER family receptors activating the pathway, and PI3K to the downstream levels of signalisation. The prognostic and predictive effect of PI3K deregulation was the central subject of the described research. The decreased expression of PIK3R1 associated with reduced survival of our patients. A special focus was put on the PIK3CA mutations which are common in breast cancer. Whereas the PIK3CA mutations act as a good prognostic marker in patients non-treated with the HER2 inhibitors, these mutations predict a negative response to trastuzumab treatment. The described results, furthermore, draw attention to the role of several altered molecular signaling pathways in breast cancer development, especially to the Wnt signaling pathway. The lapatinib plasma levels showing the relevant increase in comparison with the already described efficient steady-state levels were also described in one of the projects. Moreover, various modifications to EGFR status assessment were compared and showed that EGFR FISH and IHC count interpretation depended significantly on method and thresholds used. All these subjects are connected by the PI3K pathway, the need to deepen current knowledge and bring new useful information applicable in future clinical practice.

Stroke is a common disorder of later life with a complex etiology, including both environmental and genetic risk factors. The inherited predisposition is challenging to study due to the complexity of the stroke phenotype. Genetic studies in an isolated population have successfully identified a positional candidate gene for stroke, phosphodiesterase 4D (PDE4D). The aim of this thesis was to identify stroke susceptibility loci and positional candidate genes, taking advantage of low genetic variation in the northern Sweden population. All stroke cases were identified in a population-based stroke registry at the northern Sweden MONICA Centre. 56 families containing multiple cases of stroke and a follow up set of an additional 53 families were used for linkage studies. For association studies, 275 cases of first ever stroke together with 550 matched community controls were included. In paper I, we used a candidate region approach to investigate the PDE4D region on chromosome 5q. Linkage was obtained with a maximum allele-sharing LOD score of 2.06; P = 0.001. However, no significant association of ischemic stroke to the previously defined at-risk allele in PDE4D was observed. We next performed a genome wide linkage scan to explore new susceptibility loci for common forms of stroke (paper II). Non-parametric multipoint linkage analysis yielded allele-sharing LOD scores > 1.2 at nine locations; 1p34, 5q13, 7q35, 9q22, 9q34, 13q32, 14q32, 18p11, 20q13. The highest allele-sharing LOD score was obtained on chromosome 18p (LOD = 2.14). Fine mapping resulted in increased allele-sharing LOD scores for chromosome 5q13 and 9q22. In the follow up analysis of the nine regions, including all 109 families, the highest allele-sharing LOD scores were obtained on chromosomes 5q, 13q and 18p although none reached the initial genome wide values. In paper III, we focused on the chromosome 5q region, and further mapping and haplotype analysis in the families was performed. A common 1 cM haplotype was found to be shared among affected members of five families. In this region only the regulatory subunit 1 of phosphatidylinositol 3-kinase (PIK3R1) gene was located. Association of three single nucleotide polymorphisms in the PIK3R1 gene to common stroke was obtained in the case-control material. Finally, in paper IV, an extended pedigree containing seven families connected to common founders eight generations back was identified by genealogical analysis, and submitted to a separate genome wide scan analysis. A significant allele-sharing LOD score of 4.66 (genome wide P < 0.001) at chromosome 9q31-33 was obtained. Haplotype analysis identified a minimal common region of 3.2 cM, which was shared by four of the seven families. These four families contained all of the primary intracerebral hemorrhagic cases present in the extended pedigree. In conclusion we have replicated linkage of stroke susceptibility to the PDE4D region on chromosome 5q, but no significant association of ischemic stroke to PDE4D was observed. Linkage analysis of stroke did not identify any new major stroke loci, indicating that multiple minor susceptibility loci in addition to the previously known locus on chromosome 5q could contribute to the disease. In the chromosome 5q region a novel positional candidate gene for stroke was identified, the PIK3R1 gene. The PIK3R1 protein has several biological actions with potential roles in stroke susceptibility. Also a novel susceptibility locus for common forms of stroke at chromosome 9q was identified in a large pedigree, which may be of special importance for susceptibility to hemorrhagic stroke.