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• Breast cancer (BC) is the most common cancer among women worldwide. • miR-21 is an oncogene that has a crucial role in the regulation of drug resistance. • Overexpression of miR-21 is linked with the development and progression of MDR in BC. Breast cancer (BC) is the most common cancer among women that is responsible for the most of the cancer-related death in worldwide. Drug resistance is remaining as a significant clinical obstacle to treat BC patients effectively. Therefore, to help overcome this problem, it is necessary to understand the mechanisms of drug resistance. microRNAs classify as highly conserved non-coding RNAs (~22 nucleotides) and interact with mRNAs-coding genes for direct post-transcriptional repression. It has been reported that miR-21 is overexpressed and also acts as oncomiR in many human malignancies by targeting of several tumor suppressor genes–associated with apoptosis, proliferation and metastasis. Specifically, it has been reported that miR-21 is responsible for the drug resistance and its overexpression is related to the development of Multi Drug Resistance (MDR) in breast cancer. In this review, we discussed about the role of miR-21 on the drug resistance of breast cancer. [ABSTRACT FROM AUTHOR]

• OSCC is the eighth most common cancer in humans worldwide. • A general finding in OSCC tumorigenesis is a variation in miRNA expression pattern. • microRNA signature has been revealed as a diagnostic tool for OSCC patients. • The modulation of miRNAs makes them as the potential tools for OSCC treatment. Oral squamous cell carcinoma (OSCC) accounts for nearly 90 percent of oral cavity malignancies and is one of the most widespread oral cancers in the world. The microRNAs (miRNAs or miRs) have an important role in cellular processes comprising cell cycle, differentiation, and also apoptosis. MiRNAs are also implicated in the progression of cancers, including OSCC, through a variety of signaling pathways. One of the most significant signaling pathways in OSCC is the PI3K / Akt pathway that has been illustrated to be under the tight regulation of miRNAs. Deregulation or activation of the PI3K / Akt pathway due to mutations has been revealed to be implicated in the development of oral cancer. According to studies, more than 47% of HNSCC and around 38% of OSCC samples indicate at least one molecular alteration in this signaling pathway. The potential of miRNAs for their use as therapeutic tools in the diagnosis as well as treatment of numerous diseases have been confirmed. In the current review, we summarize miRNAs and their possible mechanisms as well as their functions in OSCC advancement and progression. [ABSTRACT FROM AUTHOR]