Tuesday, August 26, 2014

What causes pancreatic cancer?

While it is virtually impossible to tell what caused a specific person to develop pancreatic cancer, there are some important principles of cancer biology that can help us understand why pancreatic cancer develops, and large population-based studies help us understand the many risk factors for this disease.

Pancreatic cancer is fundamentally a disease caused by damage to the DNA (mutations). These mutations can be inherited from mom or dad, or they can be acquired as we age. First, let us look at the inherited mutations. Remember that we have two copies of each gene - one copy we inherit from mom, the other copy we inherit from dad. Most individuals with an inherited cancer syndrome inherit one mutant copy (let us say from dad) and one intact (normal) copy (let us say from mom) of a cancer associated gene. As they age, some of these people will damage the good copy of the gene (the copy they got from mom) in a cell in their pancreas. That cell will have two bad copies of the gene, and, as a result, that cell in the pancreas will grow into a cancer. It doesn’t mean that everyone with an inherited predisposition will get cancer, it means that since they only have one copy of the gene, they are more likely to get cancer. I like to think of it using the analogy of the space shuttle, with the shuttle standing in for a person, and computers on the space shuttle standing in for genes. Normally the shuttle goes into space with a computer and a back-up for that computer. Only if both computers break is there a problem. For people with a genetic predisposition to pancreatic cancer, it is like going up into space with one good computer and one bad computer. If something goes wrong with the one good computer, they are in trouble.

The second way we can damage our DNA is with our behavior. The carcinogens in cigarette smoke can damage our DNA. If the carcinogens damage a key cancer-associated gene in a cell in the pancreas, then that cell may grow into a cancer. Simply put, don’t smoke! The third way our DNA gets damaged is by chance. This is probably the least satisfying explanation, but it is true. Every cell in our body (and there are trillions of them!) contains a 23 chromosomes and these 23 chromosomes contain 3 billion base-pairs of DNA. Every time a cell divides it has to copy all of that DNA (so that it can make a daughter cell with a full complement of DNA). The DNA copying machinery in cells is pretty darn good, but it is not perfect. Occasionally mistakes are made. On one hand, this is good from a population or species perspective, because these mistakes allow for evolution to occur (if we copied our DNA perfectly we would not evolve!). If one of these chance errors in copying (DNA mutations) damage a key cancer-associated gene in a cell in the pancreas, then that cell may grow into a cancer.

To summarize, pancreatic cancer is caused by DNA mutations, and there are three ways that we can damage our DNA. We can be born with a DNA mutation inherited from mom or dad, we can do something, like smoke, that damages our DNA, or our DNA can be damaged by chance.

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