Cancer is a group of diseases in which cells are aggressive (grow and divide without respect to normal limits), invasive (invade and destroy adjacent tissues), and sometimes metastatic (spread to other locations in the body). It is used to describe any malignant growth or tumor caused by abnormal and uncontrolled cell division. Cancer is closely associated with cells that fail to follow the normal script for cell death and instead just keep reproducing. It is a failure of multicellular life and related to the breakdown of the mechanisms a multicellular organism uses to protect itself from evolution. Multicelluar life requires the loss of cell autonomy, which means lack of self-reproduction and programmed cell death (or Apoptosis) for the majority of cells.
- a rocket is a based on self-propulsion, which means controlled flow of fuels and propellants which leads to explosion (i.e. controlled explosion)
- a living being is based on self-replication, which means controlled flow of nutrients which leads to growth (i.e. controlled growth)
- a software is based on self-control, which means controlled flow of instructions which leads to features/bugs (a bug is sometimes called an undocumented feature)
One mechanism of self-rejuvenation is telomerase, an enzyme that prevents wear and tear damage in chromosomes, the giant molecules of DNA that embody the genetic information. The tips of chromosomes wear down and telomerase helps to replenish them, keeping them at a proper length. It produces tiny units of DNA which seal off the tips of chromosomes. These DNA units, known as telomeres, act like the plastic caps at the ends of a shoelace, keeping the chromosomes from fraying and the genes inside them from unraveling. Telomerase is usually active only in stem cells or at the beginning of life, then the telomeres get shorter each time a cell divides. Therefore they serve as a kind of clock that counts off the cell’s allotted span of life. If they get too short, a cell cannot divide again. Among others, tumors somehow turn on the telomerase gene, providing a cell with an unlimited life span. If cancer cells do not reactivate the telomerase gene, then their telomeres would get steadily shorter, forcing them into senescence and death.
Self-rejuvenation seems to be so dangerous that bodies use a fine-tuned trade-off between rejuvenation and aging in form of stem cells. Switching off telomerase everywhere in the body is problematic because it would lead to aging and impair the abilities of self-regeneration and self-reproduction. Switching it on everywhere in the body would help to treat aging, but it would be problematic too, because it would lead unintended consequences in form of cancer. Life has found a trade-off in form of a limited number of very powerful and dangerous stem cells, which possess the ability of self-reproduction.