PHILADELPHIA — Since Darren Daulton succumbed to brain cancer on Aug. 6, heartfelt tributes have honored the way he led a raucous Phillies team to the World Series in 1993.

And unanswered questions have surfaced about the way he died.

Daulton and several prominent contemporaries in baseball — including at least three other Phillies who played at Veterans Stadium, the team’s home from 1971 to 2003 — have died of glioblastoma, according to news media accounts. It is considered the most aggressive and frequently diagnosed form of malignant brain tumor.

Researchers who have examined the baseball cases for years say there is insufficient evidence to determine whether they represent anything more than coincidence. Possible cancer clusters are notoriously hard to prove. Most of the time, upon rigorous examination, no cause can be identified and the cases are considered random.

“There is almost never an explanation for them,” said Timothy R. Rebbeck, a cancer epidemiologist at Harvard and the Dana-Farber Cancer Institute who has studied the Phillies cases.