Cancer and cell phones - I meant to blog about this for some time, since it has long trended among the most read articles at the Times website.
To be charitable, the article did make me go and look up the literature, so that's not a bad thing. In short, however, the Times treatment is irresponsible and fear-mongering.
First, let me remark that the Times article mentions by name a refereed study of cellphones in humans only in the 14th paragraph. And it neglects to mention the multiple studies which have shown no connection.
Now, let's consider the INTERPHONE study referred to in the Times piece (it's one of these with the fake acronyms). It showed no connection between cell phone use and cancers, when all brain cancers are taken together. Now, it's reasonable for them to analyze different cancers separately, since they are of different severity and prevalence. It's not questionable in itself that they looked at an effect on gliomas. However, this effect was not significant. Only when they looked at cell phone use for 10 years or longer did they find an association with gliomas.
Several caveats - screaming sumo-size caveats - were not mentioned in the Times piece. (A science reporter presumably would have read the article.)
1. As far as I can figure out from reading the article, it's a secondary analysis. There was no a priori hypothesis that cell phone use for 10 years would be associated with glioma. Post hoc analyses are suspect - as you know - since data mining is biased. How many associations were fished through and discarded before this positive one was found? There is always a probability of a false positive, so if there were twenty post-hoc associations (properly consigned to an on-line appendix, pace the Times's conspiratorial mutterings), the chance of one positive finding is 5% - just by probability.
2. The association itself is not statistically significant! This is mentioned nowhere in the Times article, but the authors of the study themselves make haste to note this up front, in the abstract - which makes them responsible. I would not call this a hook to hang anyone's hat on.
3. The INTERPHONE study is a case-control study. A big question in any study of this kind is how we are to judge the accuracy of the cases' self reporting. People with cancer are understandably eager to find a cause, and might recall cell phone use out of proportion to the controls. Such recall bias is hard to control for.
4. Even if recall bias is controlled for, the correlation between recollected number of cell phone calls and the actual number of cell calls is not perfect. Heavier cell phone users tend to overestimate the number of calls they have made. In addition, the correlation between subject recall and their actual exposure to electromagnetic frequency is not airtight either.
5. Let's say the effect is real (which I very much doubt by reason of the sumo caveats just mentioned). (This would contradict another case-control study done on the very relationship between gliomas and cell phone use, in 2005, which was negative.) How high should this putative danger even rank on our public-health agenda? Gliomas are rare.
To quote a 2004 study in the journal Cancer (first thing I could Google): "The incidence rate of central nervous system (CNS) tumors in 2000 was 6.7 per 100,000 persons as reported from the Surveillance, Epidemiology, and End Results (SEER) registry and gliomas account for approximately 51% of all CNS tumors.". Let's say then 3.5 per 100,000 people. or 10,000 cases a year, more or less. Horrible cases to be sure. If cell phone use increased this number to 20,000 cases a year that would be a tragedy, but a tragedy comparable to the million deaths caused yearly by malaria?
6. In toto: bullshit.
Update: but see some second thoughts here.
Showing posts with label cancer. Show all posts
Showing posts with label cancer. Show all posts
9/21/04
Pollution and cancer in China
The recent article in the Times is harrowing, starting from its title. But the scientific questions it raises are just as important as the sympathy and disquiet it evokes. There are two issues here. First, what is the relationship between the recent increased pollution in rural China and cancer rates (or death rates due to cancer) in those regions? Secondly, apart from the epidemiologic facts, why are the people interviewed in the article so sure that they have cancer?
A brief, incomplete survey of the epidemiologic literature (oh, let me come clean here: I just went to Medline, typed in "China+epidemiology+pollution," and read a bunch of abstracts. It's Google for epidemiologists!) indicates both rather more and less than is pointed to in the Times. The rural residents complain of gastric and other GI cancers, and the available literature (much of which is, not surprisingly, available only in translated abstracts of Chinese-language articles) points to increased rates of esophageal cancer after exposure to polluted water. (I should note that the tricky part of epidemiology is figuring out the contribution of many different factors. "Correlation does not imply causation" might be tattooed on the body of every epidemiologist.)But there are also a number of articles which point to a broader array of deleterious effects, from nasopharyngeal cancer to hepatitis B infection (which can lead to primary liver cancer). A few studies, as well as the Times article, mention what would seem to be a more acute endpoint: frank toxicity due to astronomical levels of various toxins, effluents, and general nasty chemicals in well- and riverwater.
The Times article implies that the rise in cancer rates due to pollution is a recent phenomenon, of the past couple of decades. I think this is true in a sense, but the sense was corrupted due to necessary abridgment for journalistic purposes. The course of events probably goes something like this: over the past few decades, maybe since the economic liberalization that was allowed during the 70s and 80s (my Chinese history is weak, but I think this is right), industrial activity has produced and allowed widespread pollution. This pollution has indeed led to increased cancer among rural Chinese -- but only because rural Chinese are living longer (due to improved nutrition and hygiene) and are thus able to develop cancer during their additional lifespan. In these polluted rural areas, it's only over the past decade or so that these cancer cases have reached a critical mass that can't be ignored.
Another possibility is that these diseases among rural Chinese, though probably to be laid at the feet of polluters (and the Chinese public-health establishment, necessarily weakened by totalitarianism -- cf. the recent SARS mess), are also caused by simple toxicity due to the ingestion of a high concentration of pollutants.
This is just rank speculation, of course, but it's speculation that I would bet Chinese public-health workers and epidemiologists have to engage in, to decide whether cancer is, in fact, pandemic in rural China and what to do about it (besides, obviously, cracking down on pollution).
* * *
It's not clear from the article in the Times that the people interviewed do in fact have cancer. (They are horribly ill, but it's not apparent from what.) I think that in some cases they might be extrapolating from changing causes of death among people they know. As the Chinese get richer, their causes of death may shift from infectious diseases (with which many rural Chinese may already be acquainted) to the so-called "diseases of affluence" -- heart disease, stroke, and cancer. As it turns out, the Chinese Red Cross recently released a study of widespread ill-health among urban Chinese. [Strangely enough, the study isn't mentioned on the CRC's Web site. Maybe it's on the Chinese site -- can anyone tell me?]
* * *
China's the most populous country in the world, with huge populations that are urban, rural, urbanizing, or migrating from city to country. I hope China deals with its public health problems in a way that will serve as a model for other systems.
The recent article in the Times is harrowing, starting from its title. But the scientific questions it raises are just as important as the sympathy and disquiet it evokes. There are two issues here. First, what is the relationship between the recent increased pollution in rural China and cancer rates (or death rates due to cancer) in those regions? Secondly, apart from the epidemiologic facts, why are the people interviewed in the article so sure that they have cancer?
A brief, incomplete survey of the epidemiologic literature (oh, let me come clean here: I just went to Medline, typed in "China+epidemiology+pollution," and read a bunch of abstracts. It's Google for epidemiologists!) indicates both rather more and less than is pointed to in the Times. The rural residents complain of gastric and other GI cancers, and the available literature (much of which is, not surprisingly, available only in translated abstracts of Chinese-language articles) points to increased rates of esophageal cancer after exposure to polluted water. (I should note that the tricky part of epidemiology is figuring out the contribution of many different factors. "Correlation does not imply causation" might be tattooed on the body of every epidemiologist.)But there are also a number of articles which point to a broader array of deleterious effects, from nasopharyngeal cancer to hepatitis B infection (which can lead to primary liver cancer). A few studies, as well as the Times article, mention what would seem to be a more acute endpoint: frank toxicity due to astronomical levels of various toxins, effluents, and general nasty chemicals in well- and riverwater.
The Times article implies that the rise in cancer rates due to pollution is a recent phenomenon, of the past couple of decades. I think this is true in a sense, but the sense was corrupted due to necessary abridgment for journalistic purposes. The course of events probably goes something like this: over the past few decades, maybe since the economic liberalization that was allowed during the 70s and 80s (my Chinese history is weak, but I think this is right), industrial activity has produced and allowed widespread pollution. This pollution has indeed led to increased cancer among rural Chinese -- but only because rural Chinese are living longer (due to improved nutrition and hygiene) and are thus able to develop cancer during their additional lifespan. In these polluted rural areas, it's only over the past decade or so that these cancer cases have reached a critical mass that can't be ignored.
Another possibility is that these diseases among rural Chinese, though probably to be laid at the feet of polluters (and the Chinese public-health establishment, necessarily weakened by totalitarianism -- cf. the recent SARS mess), are also caused by simple toxicity due to the ingestion of a high concentration of pollutants.
This is just rank speculation, of course, but it's speculation that I would bet Chinese public-health workers and epidemiologists have to engage in, to decide whether cancer is, in fact, pandemic in rural China and what to do about it (besides, obviously, cracking down on pollution).
* * *
It's not clear from the article in the Times that the people interviewed do in fact have cancer. (They are horribly ill, but it's not apparent from what.) I think that in some cases they might be extrapolating from changing causes of death among people they know. As the Chinese get richer, their causes of death may shift from infectious diseases (with which many rural Chinese may already be acquainted) to the so-called "diseases of affluence" -- heart disease, stroke, and cancer. As it turns out, the Chinese Red Cross recently released a study of widespread ill-health among urban Chinese. [Strangely enough, the study isn't mentioned on the CRC's Web site. Maybe it's on the Chinese site -- can anyone tell me?]
* * *
China's the most populous country in the world, with huge populations that are urban, rural, urbanizing, or migrating from city to country. I hope China deals with its public health problems in a way that will serve as a model for other systems.
Subscribe to:
Posts (Atom)
