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Cancer is a medical condition which has a molecular basis. Proto-oncogenes are the first regulatory factors of this biological process. They act in transmitting signals, resulting as growth factors. Modifications of these genes, called oncogenes, lead to the appearance of cancer cells. The activation process leading to proto-oncogenes are chromosomal translocation, point mutation, and gene amplification. Concerning the clonal theory of oncogenesis, it is believed that a tumor starts from a cell. Furthermore, there is close association between tumor development and inhibition of apoptosis or programmed cell death, providing cell immortality. Angiogenesis and angiogenic factors found to be expressed in tumors and may play a key role in tumor formation and development. Tumor-suppressor genes block the growth of cancer and contribute to the normal development of cells. This article highlights the evidence that neoplasms develop as the after-effect of the increase of acquired and physical genetic variations in proto-oncogenes and tumor-suppressor genes; these form a target group in the cells of neoplasms. Tumor formation and development are characterized by individual processes, working synergistically, and an understanding of each individual process may provide a better basis for further anticancer research., (Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Aim: To provide a review considering microRNAs regulating oncogenes and tumor suppressor genes during the different stages of cell cycle, controlling carcinogenesis., Methods: The role of microRNAs involved as oncogenes' and tumor suppressor genes' regulators in cancer was searched in the relevant available literature in MEDLINE, including terms such as "microRNA", "oncogenes", "tumor suppressor genes", "metastasis", "cancer" and others., Results: MicroRNAs determine the expression levels of multiple cell cycle regulators, such as cyclins, cyclin dependent kinases and other major cell cycle activators including retinoblastoma 1 (RB- 1) and p53, resulting in alteration and promotion/inhibition of the cell cycle., Conclusion: MicroRNAs are proven to have a key role in cancer pathophysiology by altering the expression profile of different regulator proteins during cell division cycle and DNA replication. Thus, by acting as oncogenes and tumor suppressor genes, they can either promote or inhibit cancer development and formation, revealing their innovative role as biomarkers and therapeutic tools., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)