This very interesting question has been explored in a paper, linked this Berkeley page : "Another perspective on cancer: Evolution within" (the paper is at the bottom of the page).
From the site:
If one of those mutations (or a series of mutations) allows its bearer to evade cell death and reproduce more prolifically than others, it will pass that mutation on to its daughter cells, and cells bearing that mutation will increase in frequency over time. Like organisms in an ecosystem, cell lineages within one's own body compete for resources. A cell lineage that gains an advantage in that competition, accumulating mutations that allow it to grab extra resources and escape the body's control mechanisms, will proliferate and may evolve into a cancerous tumor.
The researchers also state that looking at cancer through the 'lens' of cellular evolution could be a major reason why a 'cure' eludes us.
Further, in this article "Connection between cancer development and Darwinian evolution explored", the authors state that:
He believes that many of our genes are constructed such that they protect against cancer in the first part of our lives, but that they are programmed for destruction as we get older.
Essentially, the article asserts that as we get better at prolonging our lives, that cancer is a means to shut down the body over a period of time. My understanding is (and I could be wrong) is that the increase in cancer incidents are an evolutionary way to put the brakes on the increasing human life span.