By Stephanie Stahl

PHILADELPHIA (CBS) —  Darren Daulton becomes the fourth former Philadelphia Phillies’ player to die from an aggressive form of brain cancer called glioblastoma.

University of Pennsylvania’s neurosurgeon John Lee says it’s not clear what causes glioblastoma, which is the deadliest form of brain cancer.

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Dalton was diagnosed four years ago and with his passing, he joins the following list of Philadelphia Phillies who lost their battle to glioblastoma: Johnny Oates, John Vukovich and Tug McGraw.

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“Although we’re getting a rash of Phillies baseball players, it’s probably just the statistical anomaly and probably nothing we would be able to prove scientifically,” Lee said.

There has been speculation that AstroTurf or some unknown toxin at the old Veterans Stadium could explain the high cancer rate.

“We currently have very little info or science to prove there’s any kind of association with brain cancer with anything that you’re exposed to,” Lee said.

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While there is no known environmental link to glioblastoma, there is some very preliminary research that steriods could increase the risk, but again, no proof.

“All these artificial drugs that boost things or make you grow. Growth hormones is another one that I’m very suspicious of perhaps in the future,” Lee said. “There are things that we potentially know or we suspect but right now we can’t really say for sure.”

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The one thing we do know, the beloved players provided plenty of good memories, and the four players who were taken too soon might just be a coincidence of bad luck.

“Unfortunately, that’s all we can say in our current state of science,” Lee said.

Other former Phillies players have had different kinds of cancer. Curt Schilling had mouth cancer that is linked to chewing tobacco. Doctors say that’s a clear connection.

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The brain cancer cases, we just don’t know what causes it, yet.

Stephanie Stahl