Beastie Boys rapper Adam Yauch -- also known as MCA -- has passed away at the age of 47. The cause of death is not known at this time, although he had been undergoing treatment for cancer since 2009, when he announced that he had a tumorous parotid gland and lymph node. He was not in attendance last month when the Beastie Boys were inducted into the Rock and Roll Hall of Fame in Cleveland.

The news was first reported on Russell Simmons' website, and has since been confirmed by multiple sources. Simmons also posted a note for Yauch on his site, writing "Adam was incredibly sweet and the most sensitive artist who I loved dearly. I was always inspired by his work. He will be missed by all of us."

The Beasties had not performed since Yauch's announcement, and it also delayed the release of the group's most recent album, 'Hot Sauce Committee, Pt. 2,' which was recorded in 2008-09 but only dropped last year.

Yauch co-founded the Beastie Boys with Mike "Mike D" Diamond and Adam "Ad-Rock" Horowitz in 1979, staring off as a hardcore punk group, but soon moving on to hip-hop on their multi-platinum debut album, 1986's 'Licensed to Ill.' The trio went on to release a total of eight full-length albums, including classics like 'Paul's Boutique,' 'Check Your Head' and Ill Communication.'

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