A ribosome is the cellular machinery responsible for making proteins. The production of new ribosomes is necessary to increase the capacity of protein synthesis during cell growth, division and differentiation. An increase in ribosome biogenesis leads to unlimited growth and proliferation of cells, and numerous studies have shown that increased ribosome biogenesis rate leads to malignant transformation. On the other hand, heterozygous mutations of a large number of distinct ribosomal protein genes show the transition from early symptoms, caused by hypoproliferation of cells, to a hyperproliferation which is a characteristic of cancer cells. Errors in ribosome biogenesis are a key event during the malignant transformation of normal cells. Activation of the p53 tumor suppressor when an error in ribosome biogenesis is present may actually constitute an important barrier to tumorigenesis. It is unclear how loss of function of the p53 tumor suppressor contributes to malignant transformation by disrupting the function of the nucleolus, a key site of ribosome biogenesis. Understanding these mechanisms is necessary for the development of effective anticancer therapy. Today, selective inhibitors of Pol I transcription are being developed, which have an advantage over classical chemotherapeutics and are very effective in the treatment of cancer. Cancer cells are very sensitive to drugs that inhibit the transcription or maturation of rRNA, and their use is very important in cancer therapy.