Thursday, June 7, 2012

Conquer cancer? Good luck with that

From the “misery loves company” file, here’s a statistic to ponder: About 40% of all Americans will develop cancer at some point in their lives. Half will be cured, and the other half will eventually succumb to it. Cancer claims more than a half-million lives in the U.S. every year—a number that seems horrendously high until you start parsing the data.

It turns out that a third of these cancer deaths are due to the use of tobacco products (mostly cigarettes). One-tenth are due to colorectal cancer, caused mostly by the wrong kind of diet (one high in meat and animal fat). By eating a low-fat, low-meat diet and ditching the ciggies,  you can cut your risk of dying from cancer nearly in half.

The remaining 1-in-10 risk of death by cancer might still seem intolerable until you consider another amazing statistic: During a lifetime of 80 or so years, the human body will produce about 10 million billion cells. On 10 million billion occasions, your cells go through their cycles of growth and division. Each division presents an opportunity for disaster—as occurred in one of my melanocytes years ago. The complexity of the cell cycle provides a lifetime of opportunity for something to go haywire in the DNA of the cell.

These numbers, taken together, lead to an interesting insight: While 10 people leading fairly virtuous lives will collectively experience 100 million billion cell divisions, cancer is likely to kill only one of them. One fatal malignancy per 100 million billion cell divisions doesn’t seem so bad—unless, of course, you happen to be the sole casualty. Our bodies place a formidable set of obstacles in the path of mutant cells, which holds fatal malignancies to a very low number.

These hurdles must be cleared one after another, forcing cells through a multistep process before they succeed in becoming truly malignant. For the few that do, our immune system usually kicks in to defend us against them. One class of white blood cell, the so-called natural killer cells, is able to recognize and annihilate these cancer cells. The potential anticancer role of these NK cells is an area of intense research, and of special interest to those working to develop therapies for advanced melanoma. This is the science that underlies the development of Yervoy and now anti-PD-1 immunotherapy (and other drugs in the pipeline). By boosting our immune system to more aggressively target cancer cells, these agents may help those of us with metastatic melanoma to live longer, possibly healthier lives.

A mutation occurs
when the genes in a cell
have been lost or damaged 
A major insight of cancer researchers over the last 20 years is that cancer is essentially a disease of damaged genes. We now know the identities of many of the culprit genes that control the behavior of cells in which they operate; more will give up their secrets in coming years. It’s an intensely complicated and expensive enterprise. Slow progress is being made in both targeted therapy, with melanoma drugs like Zelboraf, and in immunotherapy. Whether any of this has a significant effect on overall cancer death rates remains to be seen, but there’s reason to be hopeful.

Cancer’s ultimate causes lie far outside the individual cell—in our environment, in the food we eat and the smoke we inhale. These origins of cancer must be addressed before substantial reductions in cancer incidence can be expected. The big decreases in cancer deaths will come from preventing disease rather than discovering new cures. This isn’t to say that cancer research isn’t worthwhile, but simply that the cellular deck is stacked against us. The amazing complexity of the human body dictates cancer’s inevitability. All complex machinery breaks down sooner or later.

This is a good point to keep in mind while reading the latest scientific results coming out of the American Society of Clinical Oncology (ASCO) meeting this week. Keep the number 10 million billion in mind. Of course we’ll get better at devising ingenious methods of treating cancer, and of course investigators will speak optimistically of the prospect of “conquering cancer.” That’s what everyone wants to hear and it keeps the money flowing into research. But 10 million billion discrete cell divisions in a world filled with countless carcinogenic agents, many of them not even recognized, is an immutable fact of life. Cancer happens. We can do better at reducing its incidence, but it’s not going to zero—not now, and not likely ever.

Given what we know about cellular biology, we must make the avoidance of preventable cancers (which include most melanomas) a higher priority and afford it the respect we heap upon the often brilliant science showcased at meetings like ASCO. Prevention and cure are not mutually exclusive, but neither should “cure” be the basket into which most of our eggs are placed. In the case of melanoma, it’s far cheaper to inform and educate the public about the risks of overdosing on UV energy, and thus to prevent malignant skin disease in the first place, than it is to treat it once it’s been diagnosed. As your grandmother might have said, an ounce of prevention is worth a pound of cure.

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