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Introduction MicroRNA-21 (miRNA-21) has been described as one of the most significantly upregulated miRNAs in human breast cancer. However, limited knowledge exists on miRNA-21 expression in breast cancer tissue after neoadjuvant chemotherapy (NAC). Purpose The aim of this study was to assess miRNA-21 expression in the tumor tissues of Brazilian patients with breast cancer who underwent NAC and its correlation with clinicopathological variables. Patients and Methods Utilizing qRT-PCR, miRNA-21 expression in tumor tissue was measured in a cohort of female patients with breast cancer who underwent NAC. The correlation of miRNA-21 expression with breast cancer molecular subtypes and other clinicopathological variables was also assessed. Results A total of 55 patients were included in the study, and 28 (50.9%) underwent NAC. miRNA-21 was upregulated in patients with breast cancer, regardless of previous exposure to chemotherapy, molecular subtypes, tumor-node-metastasis (TNM) staging and lymph node status of the axilla. miRNA-21 expression did not differ between patients with breast cancer who achieved a pathologic complete response after NAC and healthy controls. Conclusion miRNA-21 was upregulated in the tumor tissue of Brazilian patients with breast cancer regardless of NAC treatment, which reinforces its role as an “oncomiR” and a potential biomarker.

Breast Cancer is a complex disease characterized by the occurrence of multiple molecular alterations. Currently, some molecular markers are in use for breast cancer diagnostic, prognostic, and predictive purposes. Thus, genetic signatures are available for improving the decision-making. The biomarkers are also essential as therapeutic approaches, but many questions remain due to the lack of efficacy on breast cancer treatment, mainly for triple-negative breast cancer subtype. Since the genetic profile of breast cancer can also be related to different ethnic groups and geographic areas, the reference populations of the genetic assays and clinical trials need to include a broader population beyond the European and North American patients. In this review, we analyzed the current and potential molecular markers that could help to improve the strategies for breast cancer therapy.

CYP2D6 is a high polymorphic enzyme from P450, responsible for metabolizing almost 25% of drugs. The distribution of different mutations among CYP2D6 alleles has been associated with poor, intermediate, extensive and ultra-metabolizers. Aim: To evaluate how missenses mutations in CYP2D6*7 and CYP2D6*14A poor metabolizer alleles affect CYP2D6 stability and function. Materials & methods: CYPalleles database was used to collect polymorphisms data present in 105 alleles. We selected only poor metabolizers alleles that presented exclusively missenses mutations. They were analyzed through seven algorithms to predict the impact on CYP2D6 structure and function. Results: H324P, the unique mutation in CYP2D6*7, has high impact in enzyme function due to its occurrence between two alpha-helixes involved in active site dynamics. G169R, a mutation that occurs only in CYP2D6*14A, leads to the gain of solvent accessibility and severe protein destabilization. Conclusion: Our in silico analysis showed that missenses mutations in CYP2D6*7 and CYP2D6*14A cause CYP2D6 dysfunction.