 MicroRNA-MIRNA-34A is a key regulator of tumor suppression. It controls the expression of numerous genes involved in cell cycle, differentiation, and apoptosis, as well as antagonizing processes essential for basic cancer cell viability in cancer stemness, metastasis, and chemoresistance. Furthermore, it can affect the responsiveness of cancer cells to chemotherapy and can be regulated by phytochemicals. Therefore, MIRNA-34A has great potential as a therapeutic agent for treating various types of cancer. This article was authored by Gabriela Miso, Maria Teresa de Martino, Giuseppe de Rosa, and others.