Baseball, Cancer, and Cancer Epidemiology

A tweep alerted me to this story from Philly.com about four Philadelphia Phillies players who all came down with brain cancer. The headline is interesting and eye-catching, in my opinion:


Screenshot of online headline

The newspaper staff had help from an epidemiologist from the University of Pennsylvania in analyzing some data:

“The rate of brain cancers in team members from that era appears to be about three times the rate in the adult male population, according to an Inquirer analysis that was reviewed by a University of Pennsylvania epidemiologist. And that elevated rate of brain cancer is statistically significant, though the analysis had certain limitations and the pattern easily could be due to chance, said Penn’s Timothy R. Rebbeck.”

I’m happy that they mention the limitations of the analysis they perform. It’s always important to say “we found X but it could have been Y and masked by Z.” Honesty is the best policy, lest someone figures out that you played a statistical trick to get the answers you wanted.

So what did they do?

“The Inquirer identified 533 men who played for the Phillies between 1971 and 2003, and tallied the number of years they have been alive since then. For those who had died, the dates of death were taken from baseball-almanac.com. Comparing cancer rates The analysis then compared the rate of Phillies’ brain cancers over that period with the rate of similar cancers in the adult male population, using data from the U.S. Census Bureau and a 2011 study in the Journal of the National Cancer Institute. The national rate was 9.8 cases per 100,000 adult males per year, while the rate in the former Phillies was 30.1 cases per 100,000 – about 3.1 times as high. The national count included various kinds of glioma, such as glioblastoma – the aggressive form of cancer that struck all four former Phillies. With Rebbeck’s assistance, The Inquirer then calculated that this 3.1 figure had a 95 percent confidence interval of 2.1 to 4.1 – meaning that the elevated rate appeared to be statistically significant.”

We need to make some assumptions here. We need to assume that exactly 533 men played for the team in that time, no more, no less. This is important since that number is the denominator. There is a huge difference between 1/2 (one half) and 1/3 (one third) by changing the denominator by just one unit. We also need to assume that exactly four (4) Phillies have ever had brain cancer, that no other player ever had cancer and that these four we know of are because they went public with it. Another thing I would have like to see is the comparison to have been done with only adults in Philadelphia, or living near the stadium. That would have given a better idea if the four players compare to their peers.

Of course, there is always the possibility of confounding. Did the players chew or smoke tobacco? Did they all live in the same neighborhood away from the stadium or share any other exposures other than playing at the stadium? Dr. Rebbeck, the epidemiologist that contributed to the investigation, goes on:

“But Rebbeck cautioned that the analysis required making certain assumptions that could substantially change the outcome. For example, the population of Phillies from 1971 to 2003 was not adjusted for age. The rate of brain cancer varies with age, so when comparing populations, it is important that they have the same distribution of people in various age groups. The Phillies in the analysis range in age from their 30s to their 70s whereas the national population number includes men above and below that. Furthermore, the nationwide brain cancer number for the 33-year period was based on cases counted in 2004 to 2007. A better approach would be to use the exact number of adult male brain cancers for each year from 1971 to 2003, as the cancer rate has declined slightly over time.”

It’s great to see all the sides being discussed, toning down the sensationalist approach to this story I feared from reading the headline.

Cancer Clusters
When people say that everyone is touched by cancer one way or another, they are not kidding. Although the rates of many cancers have been going down, there is still plenty of cancer to go around. It’s almost certain that a friend or relative of yours had or has or will have cancer. Cancer is not a monolith, either. It is a collection of diseases all characterized by the uncontrolled growth of cells. That’s why there is skin cancer, liver cancer, lung cancer, bone cancer, etc. Each tissue in our body is capable of becoming cancerous, and there is a different approach to each cancer (and even multiple approaches to the same cancer, depending on how advanced it is).

Cancer clusters and the fear that they bring with them are not a new thing. When people start seeing their neighbors coming down with one type of cancer or another, they start wondering if there is an increased risk of cancer in their neighborhood or community. Many times, what is happening is that the observer and their neighbors are growing older together. Certain cancers, because we are exposed more to triggers like the sun or smoking, appear with more frequency with age. Nevertheless, it falls on the public health authorities at all three levels of government to investigate these clusters (much in the same way as the paper did with the assistance of Dr. Rebbeck), and go from there. In my experience, most suspected cancer clusters don’t pan out.

What’s Next?
I don’t know what is next in this case, if anything is to be done at all. If it were up to me, and only me (as my opinions do not necessarily reflect those of anyone around me), I would 1) confirm the diagnosis and make sure that all four brain cancers are the same cancer and not a metastasis (spread) from a different cancer, like lung cancer going to the brain, 2) survey the other players who have played at the stadium and see if any of them developed the same type of cancer as the four in question, 3) look at the rates of cancer in general and brain cancer in particular around the stadium and around Philadelphia, and 4) determine if there are or were any known carcinogens (cancer-causing chemicals) to which the players were exposed. Imagine if they all chewed the same kind of tobacco or lived near the same source of carcinogenic “stuff,” whatever that may be.

One Last Thing
The way that this study was done seems to be as thorough as it could be without a legion of epidemiologists and biostatisticians doing the investigation. Again, my opinion. As such, one should be careful to draw conclusions from it. Is the stadium the source of their cancer? We don’t have evidence to show that it is. Are baseball players at higher risk for brain cancer? We don’t have evidence to show that they are. Should more be done? It depends. You have to confirm the diagnosis and refine the data mining techniques, like I suggested above. All in all, this was less “scary” thank I thought it would be.

Photo credit: bunkosquad / Foter / CC BY-NC-ND

I'm a fourth-year doctoral candidate in the Doctor of Public Health program at the Johns Hopkins University Bloomberg School of Public Health. All opinions posted here are my own, of course, and they do not necessarily reflect the opinions of my school, employers, friends, family, etc. Feel free to follow me on Twitter: @EpiRen

2 thoughts on “Baseball, Cancer, and Cancer Epidemiology

  1. A further confounding factor is the fact that spring training was conducted in Florida. That adds in many additional factors to consider.
    That legion of epidemiologists and biostatisticians would sound like a good idea, save for the weakness in the studies conducted by the news organization.

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    • I was thinking about that. How many other things in common did they share, and were those controlled for? I think not.

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