Enabling Replicative Immortality

This natural limitation is due to two barriers to proliferation, namely, cell senescence and cell death. Unlike normal cells, tumor cells are capable of unlimited replication. Normally, cells exhibit a limited number of growth-and-division cycles. Several data document that telomeres and telomerase, which protect the free ends of chromosomes, are involved in the replicative immortality of cancer cells (Hanahan and Weinberg 2011).