Cancers and the concept of cell senescence.

The post-mitotic cell reached by normal cell populations after serial divisions has been regarded as the hallmark of cell senescence. It was proposed that this non-dividing cell is a mechanism of protection against malignant transformation and different approaches have been used to induce the post-mitotic state. There are contradictions and paradoxes between the concepts and the data, which are described herein. There are also contradictions between data from different laboratories that attempted to identify the mechanisms leading to the post-mitotic cell. The contradictions are bypassed with the claim that there are different pathways to cell senescence. The contradictions and the differences between the data should be explained before these phenomena can be understood.