Objective: Drosha is a protein that plays a key role in the biogenesis of microRNAs which are well known to be deranged in human breast cancer. The purpose of this study was to investigate the hypothesis that Drosha is significant in the development and progression of breast cancer and has clinical relevance as a potential predictive and prognostic target. Method: We have examined Drosha protein expression, using microarray and immunohistochemistry, in a well-characterised series of unselected invasive breast cancer patients (n=750) with long-term follow-up and documented expression characteristics for a large range of biomarkers of known relevance in breast cancer. Furthermore, a smaller cohort of selected breast cancer cases (n=24) was also investigated for differential Drosha protein expression in distinct stages of tumour progression, including in situ (DCIS), invasive and metastatic components. Results: Drosha cytoplasmic and nuclear expression was lost with cancer progression, and was associated with loss of BRCA1 expression. Multivariate statistical analyses showed that Drosha cytoplasmic expression was an independent predictor of breast cancer specific survival, tumour recurrence and metastases. Conclusion: Drosha cytoplasmic expression in breast cancer is an independent predictor of patient outcome, tumour recurrence and metastasis. These observations imply that alterations in mechanisms of miRNA regulation can influence tumour behaviour. Objective: Determination of proliferation in breast carcinomas is highly prognostic and can have treatment implications. However, there is no consensus on issues such as counting area or cut-off values. Our aim was to examine and compare Ki-67 counts in various tumor areas, the novel mitosis marker PHH3, and standard mitotic count. Method: We examined a nested case-control series (n= 190) as part of the population-based Norwegian Breast Cancer Screening Program. Mitotic count (mitosis per mm2) was assessed on H&E-sections. The percentage of Ki-67 positive nuclei among 500 tumor cells was recorded for both hot-spots (HS; highest proliferation) and cold-spots (CS; lowest proliferation). PHH3 counts (per mm2) were evaluated by immunohistochemistry. Results: The upper quartiles for Ki-67-HS, Ki-67-CS, PHH3 and mitotic count consistently showed the strongest associations with known unfavorable tumor features (high histologic grade, ER negativity, HER2 positivity, CK5/6+, P-cadherin+). Univariate survival analysis showed comparable prognostic strength of Ki-67-HS, PHH3 count and mitotic count. In multivariate analysis, mitotic count was the strongest prognostic factor among these. Conclusion: By upper quartile, Ki-67-HS, PHH3 and mitotic count all showed strong associations with various tumor features. In multivariate survival analysis, mitotic count was the strongest proliferation marker. Objective: Ki67 LI is a good marker of breast cancer prognosis. We aimed at comparison of performance of 5 Ki67 antibodies. Method: 283 breast cancer cases were retrieved. Immunohistochemical staining for 5 Ki67 clones (30-9, B56, MIB1, polyclonal, SP6) performed in TMA-s in automated immunostainer. Evaluation performed on digital slides utilizing linear 0-10 frequency score. Objective: In breast cancer, classification systems are used to assess pathological response to neoadjuvant chemotherapy. Biomarkers are still needed to better predict the efficiency of primary systemic therapy. Dysregulation of connexin (Cx) channels (gap junctions) is involved in carcinogenesis and tumor progression. Method: We have correlated Cx expression and the pathological response in neoadjuvant treated breast cancers. Fifteen of the 21 human Cx isotypes were pre-screened. Cx26, Cx32, Cx43 and Cx46 were found widespread and tested in tissue microarrays of 96 breast cancers prior to and after neoadjuvant chemotherapy. Pathological response was characterized according to the EWGBSP, CPS-EG, Miller-Payne, Sataloff, and NSABP classification systems. Results: Only the CPS-EG classification had prognostic relevance by score 1-2 cases presenting better overall survival (p=0.015) than those scoring 3-5. Cx43 levels prechemo correlated with hormone receptor status pre-and post-chemo and had inverse correlation with HER2 levels pre-chemo. Reduced Cx26 expression (<5 %) post-chemo correlated with better overall survival (p=0.011). Moderate or higher Cx46 expression (>20 %) pre-and post-chemo was also associated with better survival in the EWGBSP TR2b (ppre=0.006), Sataloff TB (ppre=0.005; ppost=0, 029) and Miller-Payne G3 (ppre=0.002; ppost=0.012) subgroups. Conclusion: Classifications combined with testing for Cx46 and Cx26 expression can improve prediction of neoadjuvant chemotherapy in breast cancer.