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Background Human Epidermal Growth Factor Receptor 2 (HER2)-positive breast cancer is notable for its aggressive behavior, however with the introduction of trastuzumab in the early 2000’s, prognosis has improved. This thesis investigates the efficacy of trastuzumab in real-world settings after its introduction and evaluates the prognostic value of molecular biomarkers, aiming to optimize treatment approaches and improve patient outcomes. Material and Methods HER2-positive patients treated in the advanced and early stages of breast cancer were retrospectively identified using Swedish patient registries and through the review of medical records. Study I included 46 patients with advanced breast cancer treated with trastuzumab between 2000 and 2007. Immunohistochemical analysis of several proteins hypothesized to be involved in trastuzumab resistance were evaluated. Additionally, gene copy number variations were analyzed using droplet digital PCR. Study II include 599 patients who received adjuvant trastuzumab between 2006 and 2014 in the Southeastern health care region, in order to evaluate the implementation of trastuzumab after its approval and to evaluate patient outcomes with regard to clinicopathological variables. Study III conducted quantitative analyses of stromal tumor-infiltrating lymphocytes (sTILs) in patients with available tumor material from the same cohort identified in study II. Additionally, a case-control study of 21 cases with 21 matched controls treated with trastuzumab were analyzed with RNA-sequencing in order to identify important differentially expressed genes. Results Study I demonstrated that trastuzumab treatment in a real-world setting had similar survival as in pivotal clinical trials. Additionally, high amplification of HER2 correlated with improved progression-free survival (PFS) and overall survival (OS) in advanced breast cancer patients and PTPN2 gain was correlated with reduced PFS and OS. Study II confirmed trastuzumab's efficacy in

IntroductionSince its introduction in standard of care, trastuzumab has revolutionized the treatment of patients with early and late stages of HER2-positive breast cancer. While the initial clinical trials were convincing and lead to major changes in practice, more knowledge on the long-term outcome and tolerability is needed. The present study was designed to assess the survival, prognostic factors and relapse patterns after the implementation of trastuzumab in a real-world cohort. MethodsAll cases of HER2-positive breast cancer diagnosed between 2006 and 2014 in the Southeast Healthcare Region of Sweden were retrospectively identified. Medical records were thoroughly reviewed with regard to clinicopathological parameters, treatments, relapse pattern and adverse events. Results643 patients were identified and 599 were eligible for analysis. Breast cancer specific survival, distant recurrence free survival and local recurrence free survival were 93.4%, 89.7% and 98.0% for trastuzumab treated patients and 87.4%, 81.6% and 87.4% in patients not treated with trastuzumab, respectively. ER status, nodal status and trastuzumab treatment were all independent prognostic factors in multivariable analysis. No new safety concerns were discovered. ConclusionThe real-world outcome of trastuzumab-treated patients with early HER2-positive breast cancer is similar to what has been previously reported in long-term follow up of prospective clinical trials. ER status, nodal status and trastuzumab treatment are independent prognostic factors for breast cancer specific mortality rate, distant recurrence rate and locoregional recurrence rate in HER2-positive patients in the trastuzumab era., Funding Agencies|Swedish Cancer Society [17-0479]; Medical research council of South-Eastern Sweden (FORSS) [RO966444]; ALF Grants Region Ostergotland [LIO795201]; Stiftelsen Onkologiska Klinikernas Forskningsfond i Linkoping [2018-12-19]

The role of the epithelial-mesenchymal transition (EMT) in cancer has been studied extensively in vitro, but involvement of the EMT in tumorigenesis in vivo is largely unknown. We investigated the potential of microRNAs as clinical markers and analyzed participation of the EMT-associated microRNA-200 ZEB E-cadherin pathway in cancer progression. Expression of the microRNA-200 family was quantified by real-time RT-PCR analysis of fresh-frozen and microdissected formalin-fixed paraffin-embedded primary colorectal tumors, normal colon mucosa, and matched liver metastases. MicroRNA expression was validated by in situ hybridization and after in vitro culture of the malignant cells. To assess EMT as a predictive marker, factors considered relevant in colorectal cancer were investigated in 98 primary breast tumors from a treatment-randomized study. Associations between the studied EMTmarkers were found in primary breast tumors and in colorectal liver metastases. MicroRNA-200 expression in epithelial cells was lower in malignant mucosa than in normal mucosa, and was also decreased in metastatic compared to non-metastatic colorectal cancer. Low microRNA-200 expression in colorectal liver metastases was associated with bad prognosis. In breast cancer, low levels of microRNA-200 were related to reduced survival and high expression of microRNA-200 was predictive of benefit from radiotheraphy. MicroRNA-200 was associated with ER positive status, and inversely correlated to HER2 and overactivation of the PI3K/AKT pathway, that was associated with high ZEB1 mRNA expression. Our findings suggest that the stability of microRNAs makes them suitable as clinical markers and that the EMT-related microRNA-200 - ZEB - E-cadherin signaling pathway is connected to established clinical characteristics and can give useful prognostic and treatment-predictive information in progressive breast and colorectal cancers.