Thursday, November 10, 2011

On cancer and heart disease

Way back when, I posted a somewhat disjointed rant about our nation's uneven progress in the war against cancer. I wrote then,
Unfortunately, any successes have been fleeting, as new carcinogens are introduced into our environment daily, and preventive behavior in general has made little progress. You can spend as many millions as you want trying to find a cure, but if the root of the problem is unchanged (or getting worse), you'll make little real progress. It's a harsh Sisyphean reality that any weed-picking gardener knows well.
In keeping with the theme of that rant, I was intrigued to see this post on the Freakonomics blog earlier this week. It adds a little bit of color (and, probably, fairness) to my earlier rant.
The age-adjusted mortality rate for cancer is essentially unchanged over the past half-century, at about 200 deaths per 100,000 people. This is despite President Nixon’s declaration of a “war on cancer” more than thirty years ago, which led to a dramatic increase in funding and public awareness.
Believe it or not, this flat mortality rate actually hides some good news. Over the same period, age-adjusted mortality from cardiovascular disease has plummeted, from nearly 600 people per 100,000 to well beneath 300. What does this mean?
Many people who in previous generations would have died from heart disease are now living long enough to die from cancer instead.
Indeed, nearly 90 percent of newly diagnosed lung-cancer victims are fifty-five or older; the median age is seventy-one. The flat cancer death rate obscures another hopeful trend. For people twenty and younger, mortality has fallen by more than 50 percent, while people aged twenty to forty have seen a decline of 20 percent. These gains are real and heartening — all the more so because the incidence of cancer among those age groups has been increasing. (The reasons for this increase aren’t yet clear, but among the suspects are diet, behaviors, and environmental factors.)
Fair point. Any time we look at a statistic like "cancer mortality rate", we need to make sure we place it in a larger context, like "overall life expectancy". It doesn't exactly mean that we've been doing a great job against cancer, it just means that we have been doing a great job against some other things, which makes our stagnation in the cancer area that much more visible and striking.

Until we as a society unlock the secret of infinite life, people are guaranteed to die from something. Even if we some day succeed in curing cancer, something else will surely show up to take its place as the leading cause of death (it might even be heart disease again). It's sad, but of course true. This dynamic is just another reminder that all statistics need context.


No comments:

Post a Comment