This past Thursday I wrote a post that generated quite a bit of back and forth in the comments section, about the supposed vaccine/autism connection. An issue that’s somewhat related to that discussion is how to decide whether an observed increase in a disease or syndrome is just a coincidence, or a meaningful pattern—and, if the latter, how to determine the cause of the uptick.
These questions are also vital in the case of the phenomenon known as the cancer cluster. One was recently in the news, a dreadful grouping of cancer cases in children residing in the smallish town of Clyde, Ohio. One family even had two children with leukemia; what are the chances of that, and what could be the cause?
The answer comes not in the mind and heart gripped with understandable fear, but in the math which says every that, every now and then, statistically speaking, there will be such an increased incidence, a cluster occurring by sheer chance. It is very difficult not to act emotionally, from the gut, and insist that where there’s smoke, there must be fire.
Cancer clusters such as the one in a 12-mile radius around Clyde are reported and investigated, as well they should be. Cancer most definitely can have an environmental cause, and if that’s the case it needs to be uncovered. But the vast majority of cancer clusters are statistical glitches, although the people involved can find that very difficult to accept. Human beings want and almost need to find a cause for horrible events (or even good ones); it’s just our nature.
But true cancer clusters that have an environmental cause have certain defining characteristics. One of the best articles I’ve ever read on the issue appeared over ten years ago in the New Yorker. Written by Atul Gawande, and entitled “The Cancer Cluster Myth,” it offers this sobering quote:
“The reality is that [cancer cluster investigations are] an absolute, total, and complete waste of taxpayer dollars,” says Alan Bender, an epidemiologist with the Minnesota Department of Health, which investigated more than a thousand cancer clusters in the state between 1984 and 1995. The problem of perception and politics, however, remains. If you’re a public health official, try explaining why a dozen children with cancer in one neighborhood doesn’t warrant investigation.
Note that statistic: more than a thousand cancer clusters in Minnesota alone in a single decade, none of them found to be anything more than statistical bumps. No doubt many people would conclude that wasn’t because some environmental problem isn’t causing them, it must be because the investigations were inadequate in some way and/or even corrupt and compromised. But I would not be among those making that claim.
What are the characteristics of meaningful cancer clusters? Red flags are rare cancers rather than common ones, the same exact type of cancer rather than ones in a generally similar category, a particular cancer in an age group or other population that doesn’t usually exhibit it, or an extraordinarily high rate (for example, one environmentally caused cluster in Turkey featured a rate 7,000 times higher than usual, although the rate needn’t be quite that high to be significant). Most neighborhood clusters almost never feature any of these characteristics.
Note that in the situation in Clyde, the involved children have many different kinds of cancer, and mostly leukemia, which is (unfortunately) the most commonly-occurring childhood cancer. And even then, the two children suffering in a single family have two different types of leukemia. The childhood cancer cluster in Clyde also involves brain tumors and lymphoma, two other of the most common forms of childhood cancer. This is highly unlikely to be a meaningful cancer cluster—although it’s completely understandable that the parents there are frightened out of their wits. But exhaustive investigations have produced no smoking gun.
That’s because there probably is none. But tell that to the parents of Clyde.
