A number of concerts in October have been cancelled as a result, reported Ace Showbiz.
Lesh made the announcement on the Facebook page of his music venue Terrapin Crossroads.
The 75-year-old musician said he got the diagnose earlier this month and went through a surgery to remove the tumor. He added that it's a non-aggressive type of cancer and that his prognosis is good.
"I am very fortunate to have the pathology reports show that the tumors are all non-aggressive, and that there is no indication that they have spread," Lesh said in the statement.
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A pair of Phil Lesh & Friends concert dates, October 25 and 26, at Terrapin Crossroads are canceled. Lesh promised to reschedule the shows "as soon as we can".
The next scheduled gig would be October 30 in New York. "Keep a lookout for a free Grate Room show before I leave for the East Coast shows," Lesh said in the post.
"I also plan to pop in and jam in the bar before we leave, so I hope to see you there at Terrapin."