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Over the eons, cells have developed complex mechanisms that identify and correct many of the glitches. But the process is not perfect, nor can it ever be. Mutations are the engine of evolution. Without them we never would have evolved. The trade-off is that every so often a certain combination will give an individual cell too much power. It begins to evolve independently of the rest of the body. Like a new species thriving in an ecosystem, it grows into a cancerous tumor. For that there can be no easy fix.
These microscopic rebellions have been happening for at least half a billion years, since the advent of complex multicellular life — collectives of cells that must work together, holding back, as best each can, the natural tendency to proliferate. Those that do not (the cancer cells) are doing, in a Darwinian sense, what they are supposed to do: mutating, evolving and increasing in fitness compared with their neighbors, the better behaved cells of the body. And these are left at a competitive disadvantage, shackled by a compulsion to obey the rules.
Mutations mostly to blame
As people age, their cells amass more potentially cancerous mutations. Given a long enough life, cancer will eventually kill you — unless you die first of something else. That would be true even in a world free from carcinogens and equipped with the most powerful medical technology.
Faced with this inevitability, there have been encouraging reductions in the death toll from childhood cancer, with mortality falling by more than half since 1975. For older people, some early-stage cancers can be cured with a combination of chemicals, radiation therapy and surgery. Others can be held in check for years, sometimes indefinitely. But the most virulent cancers have evolved such wily subterfuges (a survival instinct of their own) that they usually prevail. Progress is often measured in a few extra months of life.
Overall, the most encouraging gains are coming from prevention. Worldwide, 15 to 20 percent of cancers are believed to be caused by infectious agents. With improvements in refrigeration and public sanitation, stomach cancer, which is linked to Helicobacter pylori bacteria, has been significantly reduced, especially in more developed parts of the world. Vaccines against human papilloma virus have the potential of nearly eliminating cervical cancer.
Where anti-smoking campaigns are successful, lung cancer, which has accounted for almost 30 percent of cancer deaths in the United States, is steadily diminishing. More progress can be made with improvements in screening and by reducing the incidence of obesity, a metabolic imbalance that, along with diabetes, gives cancer an edge.
Surprisingly, only a small percentage of cancers have been traced to the thousands of synthetic chemicals that industry has added to the environment. As regulations are further tightened, cancer rates are being reduced a bit more.
Advances in the science will continue. For some cancers, new immune system therapies that bolster the body’s own defenses have shown glints of promise. Genomic scans determining a cancer’s precise genetic signature, nano robots that repair and reverse cellular damage — there are always new possibilities to explore.
Maybe someday some of us will live to be 200. But barring an elixir for immortality, a body will come to a point where it has outwitted every peril life has thrown at it. And for each added year, more mutations will have accumulated. If the heart holds out, then waiting at the end will be cancer.