Decades ago some author said the average person gets cancer every day. Now, I'm the first to admit my knowledge of biology is sketchy. Even so, that statement is probably true. Normal cells of the human body will reproduce themselves a few dozen times during a person's lifetime. Part of that process of reproduction (all cells have to do it, or else there would be no life) involves the intricate workings of the DNA molecules. During all this "word processing," if you will, mistakes are inevitable. The cell has many was to repair damage. It's not perfect, but it catches a lot of of the errors. The point of this long-winded paragraph (Be patient, here it comes!) Cancer is due to an errant cell that reproduces out of control. The normal body is highly effective in nipping these problems in the bud. So in a sense, we probably get a seed of cancer everyday, but 99.9999999999% of the time the body catches and fixes the error in time.