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Yes bassist and founding member Chris Squire will undergo treatment for cancer. According to a message on the prog-rock band’s official website, Squire has been diagnosed with acute erythroid leukemia, a form of acute myeloid leukemia. He will be treated in his hometown of Phoenix over the next few months.

Squire formed Yes in 1968 with singer Jon Anderson and would remained the sole constant factor in the act’s subsequent multitude of lineups, playing on all of the band’s albums, including 1971’s Fragile, 1972’s Close to the Edge, 1977’s Going for the One, and 1983’s 90125, which contained the #1 hit single “Owner of a Lonely Heart.”

Yes has announced that its summer tour will go on as planned with Billy Sherwood, who has previously played guitar and keyboards with the band, stepping in as Squire’s replacement.

“This will be the first time since the band formed in 1968 that Yes will have performed live without me,” Squire said in a statement. “But the other guys and myself have agreed that Billy Sherwood will do an excellent job of covering my parts and the show as a whole will deliver the same Yes experience that our fans have come to expect over the years.”