Conductor Michael Tilson Thomas prepares backstage prior to performing with the YouTube Symphony Orchestra at Sydney Opera House in 2011 in Sydney, Australia.

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Conductor Michael Tilson Thomas prepares backstage prior to performing with the YouTube Symphony Orchestra at Sydney Opera House in 2011 in Sydney, Australia. / Getty Images

The eminent conductor and composer Michael Tilson Thomas has publicly confirmed that he's been diagnosed with glioblastoma multiforme, a type of aggressive brain cancer. Tilson Thomas served as music director of the San Francisco Symphony for 25 years, until June 2020.

Word began circulating of Tilson Thomas's illness in the classical music community last year, when he underwent surgery for the removal of a tumor, but no official diagnosis was disclosed until he released a public letter Wednesday to supporters and fans.

"It takes strength to meet the demands of the music and to collaborate on the highest level with the remarkable musicians who so generously welcomed me," he wrote, of the 20 concerts he's performed over the past few months with the New York Philharmonic, the Los Angeles Philharmonic, and the San Francisco Symphony. "I now see that it is time for me to consider what level of work and responsibilities I can sustain in the future."

"Currently the cancer is in check," Tilson Thomas wrote. "But the future is uncertain as Glioblastoma is a stealthy adversary. Its recurrence is, unfortunately, the rule rather than the exception."

Tilson Thomas is the co-founder and longtime artistic director of the New World Symphony, a training orchestra for emerging professional musicians based in Miami. He said in the letter that he's undergone an operation, radiation treatment and chemotherapy. "After 34 years, I will be stepping down as the Artistic Director of the New World Symphony," he wrote.

Constance Shuman, Tilson Thomas's representative, told NPR that the conductor plans to continue leading the New World Symphony as much as he can from behind the podium, but will pass off administrative duties. He will become the organization's Artistic Director Laureate; Tilson Thomas holds laureate titles with the San Francisco Symphony and the London Symphony Orchestra as well.

"I intend to stick around for a bit," Tilson Thomas wrote. "Creating and collaborating to make great music is what it's all about for me. ... I will continue to compose, to write, and to mull over your thoughts and mine. I'm planning more time to wonder, wander, cook, and spend time with loved ones — two legged and four. Life is precious."

In the letter, Tilson Thomas thanked his colleagues for their support, as well as his husband, Joshua Robison.

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