Molecular biology of cancer cell is a domain of medical science that is rapidly growing in our days. Knowing the ways and paths that cancer cells follow is crucial to the prevention of cancer itself. Central role to these paths, concerning the cell cycle and the process of apoptosis, has the protein p53. The whole mechanism of the cell cycle is activated by the action of various mitogens, such as growth factors, hormones and cytokines. Carcinogenesis involves alterations of genes (proto-oncogenes and tumor suppressor genes), which encode proteins of the signal transduction. Many of the damages that lead to carcinogenesis may be due to the lack of repressive signals for cell division, but also to the absence of the sensitivity of cells to repressive signals. The cell has mechanisms of receiving apoptotic-antitumor signals and mechanisms of execution of these instructions. A percentage of cancers (4-8%) are etiologically linked to germ (stem) cells mutations and occur at an increased frequency in families (hereditary cancers). Substantial progress in understanding the mechanisms of carcinogenesis, filtration and metastasis of cancer has highlighted the key role of specific genes, primarily oncogenes and tumor suppressor genes.