Drug resistance remains a burden in cancer treatment. In the past few years molecular genetics brought a new hope with personalized therapy. This individual approach allows the identification of genetic profiles that will respond better to a given treatment and consequently get a better outcome. Recently, physicians received an extra aid with the approval of molecular tools based on gene expression signatures. With these tools, physicians have the capacity to identify the probability of disease recurrence in the first 5 years following diagnosis, a fact that is essential for a more effective adjuvant therapy administration. However, some patients still relapse and acquire drug resistance and aggressive tumors. For that reason, a comprehensive understanding of the molecular players in drug resistance is of extreme importance. Micro RNAs have been described as regulators of various cellular pathways and as predictive and prognostic factors. As broad regulators, microRNAs also interfere with drug metabolism and drug targets. Thus it is of paramount importance to understand which micro RNAs are deregulated in breast cancer and try to relate this mis expression with resistance to therapeutics, poor outcomes, and survival. Here, we describe a possible approach to study micro RNA expression and respective targets from formalin-fixed, paraffin-embedded (FFPE) breast cancer tissues. FFPE tissues are regularly archived for long periods in pathology departments, and microRNAs are well conserved in these tissues.